Qixing Jiang

This study investigated the effects of chitosan-based coatings on flavor retention of refrigerated grass carp fillets by using various indicators: free amino acids (FAA), nucleotides, trimethylamine (TMA), volatile profile, sensory quality, and electronic nose analysis. The results indicated that chitosan-based coatings contributed to the significant reduction of off-flavor compounds, such as TMA, hypoxanthine (Hx) and histidine, and accumulation of inosine monophosphate (IMP) and umami-associated FAA. GC–MS analysis showed 23 volatile organic compounds, including many C5–C9 aldehydes and alcohols in the fresh fillets. The coating treatments, especially chitosan-clove bud essential oil composite coatings, sharply reduced the relative content of off-odor volatiles, such as hexanal, octanal and 1-octen-3-ol. According to the results of the sensory evaluation and electronic nose analyses, chitosan coating combined with glycerol monolaurate and clove bud essential oil was a promising method to improve the edibility of grass carp fillets by maintaining flavor quality during refrigerated storage.

Monodispersible selenium nanoparticles (SeNPs) were synthesized by using chitosan (CS) and carboxymethyl chitosan (CCS) as the stabilizer and capping agent using a facile synthetic approach. The structure, size, morphology and antioxidant activity of the nanocomposites were characterized by transmission electron microscopy (TEM), Ultraviolet-visible spectroscopy (UV-vis), Dynamic Light Scattering (DLS), Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA). The results revealed that the monodispersible SeNPs (mean particle size of about 50 nm) were ligated with CS and CCS to form nanocomposites in aqueous solution for at least 30 days, and for 120 days the nanoparticles increased to 180 nm or so in size. The DPPH scavenging ability of CS-SeNPs was higher than that of CCS-SeNPs, and could reach 93.5% at a concentration of 0.6 mmol/L. Moreover, SeNPs, CS-SeNPs and CCS-SeNPs exhibited a higher ABTS scavenging ability in comparison to Na2SeO3.

To deal with serious environmental damage resulting from plastic packaging materials, biodegradable films using natural products have gained considerable attention. Here, we provide a simple, fast, and environmentally-friendly route to construct a biodegradable film using chitosan (CS), bacterial cellulose (BC), and curcumin (Cur). Composite films (CSn-BC-Cur) using CS with different molecular weights were investigated, and their water moisture content (MC), water solubility (WS), contact angle (CA), mechanical properties, barrier properties, and antioxidant properties were compared. The obtained films were characterized by SEM, XRD, and TGA. The results showed that chitosan with a higher molecular weight presented higher contact angles and mechanical properties, along with a lower moisture content, water vapor transmission rate, and oxygen transmission rate. Furthermore, when the composite film was placed in 95 % ethanol, it released active substances. The results suggest that these composite films can be used as promising materials for food packaging.

This study aimed to develop a chitosan/zein based bilayer film loaded with nanoparticles (0, 1, 2, and 3%) as a reinforcing and functional agent and to investigate the effects of NPs on the physicochemical properties and structural attributes of the film. Curcumin-loaded pectin-based nanoparticles (NPs) with antimicrobial nisin were prepared using a combination of anti-solvent precipitation and complexation, and embedding NPs into the chitosan matrix to improve the physicochemical and functional properties of the chitosan/zein bilayer films. The average particle size and ζ-potential of the NPs were 143 nm and −33.0 mV, respectively. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed that the NPs had good compatibility with the film matrix and filled void spaces in the film matrix, which significantly improved the mechanical properties of the bilayer films (elongation at break increased from 63.2 to 86.8%; tensile strength increased from 32.4 to 45.1 MPa). The NPs bilayer films had higher barrier properties and thermal stability as well as UV blocking properties compared to bilayer films without NPs, while the controlled release of the active agents was sustainable. Likewise, the antimicrobial activity against the food-borne pathogens Staphylococcus aureus and Escherichia coli and the antioxidant activity of the NPs bilayer films depended on the NPs loading. The results suggested new design principles for chitosan/zein bilayer biofilms for potential use with sustainable food packaging, where the properties of the bilayer films could be tailored by controlling the concentration of NPs.

Maximizing the waste valorization of renewable resources to develop biocomposite materials is highly desirable regarding environmental sustainability and food chain security. Herein, lignin nanoparticles (LNPs) obtained using deep eutectic solvent (DES) by anti-solvent strategy were employed as nanofillers in the chitosan matrix to fabricate novel bioactive packaging films. The results showed that adding LNPs reduced the swelling degree and water vapor transmittance of chitosan films. Upon introduction of LNPs content, the tensile strength of the composite films significantly increased by about 40%, whereas the elongation at break showed an opposite trend. When the content of LNPs was 10 wt %, the UV shielding and free radical scavenging ability of the composite films reached the maximum point. However, the diameter of the inhibition zone only increased at the addition of 1 wt%. Furthermore, the refrigerated (4 ± 1 °C) grass fish wrapped with composite films revealed better quality and the shelf life was extended to 10 days. Therefore, nanocomposite films provide an attractive and promising pathway for high value-added commercial utilization of lignin and chitosan for food packaging applications.

The main goal of this study was to investigate the dynamics, diversity and succession of microbial community present during the preparation of Suan yu (fermented fish), with and without starter cultures by high-throughput sequencing of 16S rRNA and ITS1 genes. Firmicutes and Ascomycota were the predominant phyla of bacteria and fungi, respectively, in all samples. At the genus level, Lactobacillus, Macrococcus and Staphylococcus were the predominating bacteria throughout the fermentation process, regardless of the inclusion of starter cultures. Saccharomyces was the predominating fungal genus in the early-fermentation stage of samples that inoculated starter cultures (MS), while the final product was dominated by Candida and Wickerhamomyces. Compared with naturally-fermented samples (NS; no starter cultures), Lactococcus, Leuconostoc, Enterococcus, Vibrio, Fusicolla and Torulaspora were inhibited and Aureobasidium emerged in samples inoculated with starter cultures (P < .05). Unweighted pair-group and principal component analyses of bacterial and fungal compositions revealed that microbiota structures differed between NS and MS samples. Redundancy analysis indicated that water content and pH might be important factors influencing the dominant bacterial and fungal community. Results indicated that microbial community were dynamic during fermentation process and the inoculation of mixed starter culture inhibited the growth of many organisms associated with food spoilage and contributed to the improvement of the quality of Suan yu products.

A novel chitosan-based coating solution was prepared by combining glycerol monolaurate (GML) for shelf life extension of refrigerated grass carp fillets. The control and coated fillets were analyzed periodically for physicochemical (pH, thiobarbituric acid (TBA) value, total volatile basic nitrogen (TVB-N) value, K value, and shear force), microbiological (total viable counts (TVC), psychrophilic bacteria counts (PTC), Pseudomonads and H2S-producing bacteria) and sensorial characteristics. The results showed that chitosan-GML coated samples presented better quality preservation effects than chitosan coating alone. In addition, 2% chitosan enriched with 0.3% GML showed the significant (P < 0.05) effectiveness in inhibiting microbial growth, nucleotide breakdown, the formation of alkaline components and texture deterioration, and maintaining sensory acceptability among the groups. These findings confirmed that chitosan coating enriched with GML was a promising method to extend the shelf life of refrigerated fillets.

To investigate the contribution of autochthonous microflora on free fatty acids (FFA) release and flavor development in low-salt fermented fish, three groups of processed fish, including bacteriostatic-acidification group (BAG), bacteriostatic group (BG), and spontaneous fermented fish (CG) were established. Results showed that addition of NaN3 reduced microbial load in BAG and BG below 3.5 log CFU/g after 3 weeks of incubation. Activities of lipases and lipoxygenase declined markedly with increasing time, where BG had the highest activities, followed by CG and BAG. There is a 36.3% higher in the total FFA content in CG than that in BAG, indicating both microbial and endogenous lipases contributed to the FFA liberation in fermented fish while endogenous lipases play a major role. However, compared to BAG and BG, largely higher levels of volatile compounds were observed in CG, suggesting that autochthonous microflora dominated the generation of volatile flavor compounds in fermented fish.

A novel water-soluble chitosan oligosaccharide (COS) derivative, chitosan oligosaccharide/kojic acid grafts assigned as COS/KA, was prepared by using the selective partial alkylation of N-benzylidene COS and chlorokojic acid in the presence of dimethyl sulfoxide (DMSO) and pyridine (Py). The derivative was characterized by UV-vis spectroscopy, FTIR, (1)H NMR, TGA, SEM, and XRD techniques, which showed that the alkylation reaction took place at the C-6 and C-3 positions of COS. The results showed that the degree of substitution (DS) for COS/KA was from 0.38 to 1.21, and the product exhibited an excellent solubility in organic solvents and distilled water. The antibacterial results indicated that the antibacterial activity of COS/KA was strengthened relative to COS with the increase of DS for Staphylococcus aureus , Escherichia coli , Aspergillus niger and Saccharomyces cerevisiae . These findings provide important supports for developing new antibacterial agents and expand the scope of application of COS in the food industry.

Fishery products are delicious, nutritional and healthy foods, and their popularity in today's market is growing. With the changes in consumer consumption expectations as well as the development of reliable cold-chains, fresh preprocessed fishery products such as fillets are more popular with consumers and producers because of their convenience for processing and cooking. However, fishery products after being removed from water have a short shelf life due to their intrinsic characteristics. Therefore, developing effective preservation technology to extend postmortem shelf life of fishery products has been an on-going area of study. This review summarizes the patterns of quality deterioration and external factors that affect postmortem quality of fishery products, and then updates the recent advances with preservation methods for fishery products including superchilling, modified atmosphere packaging, active packaging, edible coatings, irradiation and high hydrostatic pressure. Moreover, the advantages and disadvantages of each technology are discussed, and future trends for improving the preservation of fishery products are also discussed.

Summary Effect of autochthonous starter cultures on the volatile flavour compounds of Chinese traditional fermented fish was studied. Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31, isolated from Suan yu, were selected as starter cultures. Volatiles were extracted by headspace solid‐phase microextraction ( SPME ) and analysed by gas chromatography–mass spectrometry technology ( GC ‐ MS ). Esters and alcohols were the main components of volatiles, accounting for over 50 percentage points in all samples. The highest content of esters (3034.54 μg kg −1 ) was observed in S1 inoculated with L. plantarum 120, while the highest content of alcohols (2164.53 μg kg −1 ) and ketones (379.98 μg kg −1 ) was detected in S3 inoculated with S. cerevisiae 31. The content of acids and aldehydes was lower in inoculated samples. Principal component analysis revealed that the volatile composition was primarily influenced by the nature of the starter cultures. L. plantarum 120 and S. xylosus 135 could accelerate fermentation.

Urea, sodium dodecyl sulfate (SDS) and N-ethylmaleimide (NEM) were employed to monitor the contributions of hydrogen bonds, hydrophobic interactions and disulfide bonds in heat-induced surimi gel. Surimi gels were prepared with the bond disrupting agents followed by texture profile, gel strength, rheological and Raman analysis. The rheological analysis demonstrated that remarkable changes of storage moduli (G′) were presented below the critical temperature, especially for SDS treatments. Gel strength significantly decreased as the concentration of urea and NEM increased, while it was slightly improved by 1% SDS. With the involvement of bond disrupting agents, hardness and gumminess of surimi gel presented a dramatical decrease. The Raman results indicated that protein secondary structure tended to transform to random coil, with content of α-helix and β-sheet decreasing. Textural properties were in correlation with protein conformation. Less of random coil led to improvement of gel strength, and springiness was mainly contributed by β-sheet and β-turn. The results suggested that different bond disrupting agents induced various changes in surimi gel properties and protein secondary structure.

The correlation between microbiota succession and flavor development in Chinese traditional fermented fish (Suanyu) inoculated with mixed starter cultures was studied. The results showed that 17 free amino acids, 22 free fatty acids and 9 organic acids were present. A total of 81 aroma compounds were detected during Suanyu fermentation. Aldehydes were the most abundant aroma compounds in the early stage of fermentation and esters contributed most to the aroma in the later stage of fermentation. The correlation analysis of microbial succession and flavor dynamics based on bidirectional orthogonal partial least squares (O2PLS) suggested that in addition to starter cultures, other microorganisms including 2 bacteria genera and 11 fungi genera were also responsible for the formation of flavor compounds. These results may help focus further research to improve the flavor quality of traditional fermented fish.

Here, a nontoxic antibacterial material based on Chitosan Oligosaccharide-N-Chlorokojic acid Mannich base (COS-N-MB) that was synthesized by using the selective partial alkylation reaction displaying excellent activity against bacterial infection. The proposed mechanism of the action of COS-N-MB is that this antibacterial material with positive charge and synergistic antibacterial effects can promote it’s adsorption to bacterial cell wall through electrostatic interaction and chelating metal cations. It changed the permeability of the membrane, caused cellular leakage, and destroyed the membrane integrity, leading to complete membrane disruption and eventually death of the bacteria. Besides, COS-N-MB can interact with membrane proteins, causing deformation in the structure and functionality. The good biocompatibility, noncytotoxic, and low hemolysis made this novel material a promising and effective compound for antibacterial applications.

Softening is always a problem in fish preservation. This study was aimed to investigate the role of myofibrillar structural proteins degradation in fish softening. The changes of myofibrillar structural proteins, muscle ultrastructure, myofibril fragmentation, and shear force were studied. The results indicated that during the superchilled preservation of grass carp (Ctenopharyngodon idella), small (low-molecular-weight) myofibrillar structural proteins like desmin and troponin-T initiated textural deterioration, leading to Z-disk weakening and actin loosening. In contrast, giant (high-molecular-weight) myofibrillar structural proteins like titin and nebulin were degraded in more amount in the later storage, contributing to Z-disk and M-band disassembly and vague of light and dark regions (I and A bands). Compared to each other, desmin and titin played more important part in softening. All these changes were involved in the increase of muscle fibril segments and the sharp decrease of shear force.

A new chitosan oligosaccharide derivative (COS-N-Ger), based on geraniol (Ger) modificated onto the NH2 position of chitosan oligosaccharide (COS) via a facile method, was prepared and employed to evaluate in vitro antibacterial activity. The structures of COS-N-Ger derivatives were confirmed by FT-IR, 1H, 13C NMR, and elemental analysis. The characterization results showed successful synthesis of derivatives and the degrees of substitution (DS) of COS-N-Ger1-3 were from 0.260 to 0.283 with the yields up to 78 %. The in vitro antibacterial activity evaluation results presented a significant inhibition effect of COS-N-Ger1-3 derivatives on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as compared to COS. Moreover, their antibacterial activities were dose-dependent and more sensitive to S. aureus than E. coli. The results provide reliable theoretical supports for exploring the application of COS derivatives in the food industry as new potential antibacterial agents.

Effects of ultrasound-assisted chitooligosaccharides (COS-UA) coating on the quality attributes and microbial composition of refrigerated grass carp fillets were evaluated. The results showed that COS and COS-UA coatings retarded quality deterioration of fillets during storage. Compared to COS coatings, COS-UA treated samples had lower contents of BAs, simultaneously their levels of total volatile base nitrogen (TVB-N), K value and total viable counts (TVC) were further decreased by 13.6%, 4.2% and 7.8% on day 12, respectively. High-throughput sequencing showed that Aeromonas and Shewanella increased rapidly in control samples and became the main microbiota at day 12. By contrast, both coatings changed the microbial composition and reduced the proportion of spoilage organisms. Based on multiple evaluations, COS-UA extended shelf life of fillets by another 2 days when compared to COS. Therefore, ultrasonic treatment could be considered as an effective supplementary to improve the preservation effect of COS-based coatings for fresh preprocessed fish.

Pickering emulsions stabilized by biocompatible and edible particles have received increasing attentions recently. The surimi particles were firstly prepared and then the physical characteristics of soybean oil-based emulsions stabilized by surimi particles were investigated. The visual observation of emulsions indicated the emulsified phase volume increased with increasing concentrations (0–4 wt%) of surimi particles. The stability index of sample with 4.0 wt% particles at 0.5 or 0.6 oil fraction (0.5–4.0% or 0.6–4.0%) reached 99.1% and 100% after 14 days storage, respectively. The confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscope (cryo-SEM) observations showed that surimi particles were anchored onto the surface of oil droplets and aggregated to form gel-like network. The droplet size of samples with varied surimi particles at 0.5 oil fraction were found in the range of 76.09–90.38 μm. Additionally, 3.5 wt% surimi particles stabilized samples at 0.5 oil fraction (0.5–3.5%) under a series of pH (3, 5, 7, 9, 11) and NaCl conditions (0.1, 0.2, 0.3, 0.4, 0.5, 0.6 M) showed similar droplet sizes but dissimilar zeta potential. The rheological results suggested the shear thinning and elastic behaviors of emulsions. Increasing either fish protein particles concentration or salt levels could decrease the T23 relaxation time of emulsions. In conclusion, surimi particles can function efficiently as edible Pickering particles to stabilize emulsions.

Biodegradable chitosan films are highly desirable for use as food packaging, but the poor mechanical properties, water sensitivity, and functional limitations of these films must be addressed. In this study, a new chitosan film was prepared from chitosan–citric acid/chitosan–adipic acid (CA) and chitosan–malic acid/chitosan–adipic acid (MA) solutions and plasticized by the incorporation of a natural betaine-based deep eutectic solvent (DES; 0–30 wt%) and lignin (1 wt%). The resultant films were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and X-ray diffractometry to evaluate the changes in the structural, physical, antioxidant, and antimicrobial properties. Analysis revealed that the films contain numerous particles in cross-section and have rough surfaces. Furthermore, the addition of 30 wt% DES with lignin resulted in a significant increase in the elasticity, water contact angle, and radical scavenging rate. Moreover, the presence of lignin in the films reduced the water vapor permeability because of its hydrophobicity. Additionally, the CA film containing lignin displayed good antibacterial activity against Staphylococcus aureus and Escherichia coli. Overall, the CA-based composite films demonstrated excellent potential for use as bioactive food packaging application.

This study aimed to reveal the effects of vacuum-impregnated carboxymethyl chitosan (CMCS) coating with pomegranate peel extract (PPE) on quality retention of fish flesh during refrigeration. Herein, CMCS-PPE coating was effective in attenuating quality loss of grass carp fillets. Compared to Control, the levels of drip loss, total volatile base nitrogen, and K value in coated samples were sharply decreased (p < 0.05) by 24.5%, 35.3% and 25.2% on day 9, respectively. Meanwhile, the coating also helped inhibit oxidation, bioamine accumulation, and texture softening in fillets. Moreover, the microbial enumeration was reduced by >1.4 lg cfu/g as compared to Control on day 6 afterward, and high throughput sequencing analysis further showed the active coating contributed to the notable growth suppression of spoilage bacteria like Shewanella. Additionally, the positive effect of the coating scheme was also verified in longsnout catfish and snakehead, further confirming its good applicability for fish flesh preservation.

Traditional chitosan-acetic film, with unpleasant flavor and poor water resistance, is limited in its application in food industry. This study aimed to explore a potential alternative to improve physicochemical properties of chitosan film. Five kinds of cross-linked chitosan films incorporated succinic, adipic, tartaric, malic and citric acid, were obtained by amidation and Maillard reactions. Compared with chitosan-acetic film, cross-linked films improved their thermal stability, swelling degree, water vapor transmission rate and light barrier, attributed to the formation of amide linkage confirmed by FTIR and XPS. Results showed that hydroxylated acid films were more elastic than non-hydroxylated films. Moreover, hydroxylated acid in film prominently decreased the swelling degree, and the lowest value (10.92 ± 0.75%) was observed in chitosan-malic film. Meanwhile, there was the highest DPPH scavenging rate of 52.19 ± 3.90% in chitosan-adipic film. Consequently, the crosslinked chitosan film with application-satisfied physical properties has a promising potential for food packaging.

This study aimed to investigate the effects of l-arginine (L-Arg) on the gel properties of reduced-salt shrimp surimi gel (SSG) treated with microbial transglutaminase (MTGase). The results showed that replacing NaCl with different concentrations of L-Arg in reduced-salt (0.5% NaCl) shrimp surimi treated with MTGase significantly increased the gel strength and texture of SSG, even at low L-Arg (0.5%) concentrations. However, 0.5% L-Arg added alone under low-salt conditions did not significantly improve the gel strength of SGG compared with the control SSG containing 0.5% NaCl. L-Arg and MTGase added together significantly increased the disulfide bonds and protein β-sheet structure of SSG while improving the moisture distribution and rheological properties. The electrophoretic analysis and microstructure images revealed that L-Arg and MTGase together promoted the cross-linking of proteins in shrimp surimi to form a dense gel network structure. In conclusion, the combined treatment of L-Arg and MTGase significantly improved the gel properties of SSG and reduced the amount of NaCl. Therefore, the combined treatment of L-Arg and MTGase could enhance the quality of reduced-salt shrimp surimi products.

In this study, three groups of mixed starter cultures (S1: Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31; S2: L. plantarum 145, S. xylosus 135 and S. cerevisiae 22; S3: Pediococcus pentosaceus 220; S. xylosus 135 and S. cerevisiae 22), isolated from Suan yu, were inoculated to produce the traditional fermented fish. After 42 days fermentation at 24 °C, Suan yu inoculated with different mixed starter cultures underwent rapid growth of lactic acid bacteria (LAB), declined pH, suppressed increase of thiobarbituric acid (TBARS) and total volatile base nitrogen (TVB-N) as well as growth of spoilage bacteria and pathogens. Besides, Suan yu had higher contents of non-protein nitrogen (NPN) and total free amino acids (FAA) compared to the control (P < 0.05). The muscle proteins were severely hydrolyzed during fermentation (SDS-PAGE). Moreover, the sensory evaluation indicates the fermented fish was more widely accepted than the control. The results suggest that the inoculation with S1, S2 and S3 reduced the lag time that fermentation began and improved the quality of Suan yu.

This paper reports the first study on the chemical and microbial properties of Suan yu, a sanitary Chinese traditional low-salt fermented whole fish product of high nutrition, unique flavor, and long-storage capability. Six brands of Suan yu from different locations in China were studied. Significant differences were observed in some characteristics of this traditional fermented fish, raw material and other spontaneously fermented fish. The values of Enterobacteria and Pseudomonads were under the detection limits in six different brands. In addition, the products contained higher protein and lower moisture ranging from 17.2% to 22.9% and 52.9%–58.1%, respectively. The pH values ranged between 4.27 and 5.18, and lactic acid was the major organic acid. The proteolysis of the myosin heavy chain and actin chain were observed through sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Moreover, low concentrations of biogenic amine (BA) and thiobarturic acid (TBARS) values were found in all samples. The characteristics of the six Suan yu brands were all influenced by raw materials, ingredients, and fermentation processes and conditions.

Two different molecular weights of chitosan were pulverized to nanopowders by ultrafine milling. The nanopowders were characterized by viscometry small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), FT-IR spectroscopy and UV–vis spectroscopy. Our results showed that ultrafine milling effectively reduced the particle size of chitosan to a nanoscale. The viscosity average molecular weight (Mv) of chitosan was decreased by the milling treatment. The crystalline structure of chitosan was destroyed by the milling since the nanopowder exhibited an amorphous XRD pattern. In addition, thermal stability of the low molecular weight chitosan was decreased after the milling treatment. FT-IR and UV–vis spectra showed that the milling process did not cause significant changes in the chemical structure of chitosan.

The novel derivatives of geraniol grafted chitosan oligosaccharide were synthesized via substitution and deprotection reaction, respectively. The products were identified by Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), X-ray diffraction analysis (XRD), Thermogravimetric analysis (TGA) and UV-vis absorption spectroscopy. It is revealed that the derivatives exhibited a good solubility, thermal stability and antibacterial properties.

Seinat ( Cucumis melo var. tibish ) seeds were analyzed for their physiochemical properties and chemical composition of the oil in addition to antioxidant activity. The crude oil content was 31.1%, while the moisture, fiber, protein, ash and total sugar contents were 4.2%, 24.7%, 28.5%, 4.3%, and 6.9%, respectively. The main fatty acids were linoleic, oleic, palmitic, and stearic acids (61.10%, 18.75%, 10.37% and 9.18%, respectively). The total phenolic content was 28.17 mg·g –1 oil. Seinat seed oil also contained a good level of tocopherols; of which δ-tocopherol (63.43%) showed the highest content. β-sitosterol was found at 289 mg·100g –1 oil of total sterols (302 mg·100g –1 ) in the oil. The crude oil showed a good antioxidant activity in four assays including reducing power, β-carotene bleaching inhibition activity, ABTS and DPPH radical scavenging activities.

The study evaluated the inhibitory effects of chitosan-based coatings on endogenous enzyme activities, proteolytic degradation and texture softening of grass carp (Ctenopharyngodon idellus) fillets stored at 4 °C for 15 days. In general, the inhibitory effects of chitosan coating were worse than that of chitosan composite coatings, which significantly inhibited cathepsin B, B + L and calpain activities of fillets, with the most reductions of 58%, 65% and 41%, respectively when compared to the corresponding values of control fillets. Besides, the treatments also retarded the proteolytic degradation through quantifiable indicators including salt-soluble proteins (SSP), TCA-soluble peptides and SDS-PAGE pattern. After storage of 15 days, the shear forces of coated fillets were 28-53% higher than that of control samples. These results indicated that chitosan composite coating combined with glycerol monolaurate and clove essential oil improved the quality of refrigerated grass carp fillets by alleviating endogenous enzyme induced proteolysis and softening.

Journal of Food Processing and PreservationVolume 41, Issue 5 e13131 Original Article Contribution of Mixed Starter Cultures to Flavor Profile of Suanyu – A Traditional Chinese Low-Salt Fermented Whole Fish Xuefeng Zeng, Xuefeng Zeng State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 China School of Liquor and Food Engineering, Guizhou University, Guiyang, ChinaSearch for more papers by this authorWenshui Xia, Corresponding Author Wenshui Xia xiaws@jiangnan.edu.cn State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 ChinaCorresponding author. FAX: 86-0510-85919121; EMAIL: xiaws@jiangnan.edu.cnSearch for more papers by this authorQixing Jiang, Qixing Jiang State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 ChinaSearch for more papers by this authorYanshun Xu, Yanshun Xu State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 ChinaSearch for more papers by this authorJing Fan, Jing Fan School of Liquor and Food Engineering, Guizhou University, Guiyang, ChinaSearch for more papers by this author Xuefeng Zeng, Xuefeng Zeng State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 China School of Liquor and Food Engineering, Guizhou University, Guiyang, ChinaSearch for more papers by this authorWenshui Xia, Corresponding Author Wenshui Xia xiaws@jiangnan.edu.cn State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 ChinaCorresponding author. FAX: 86-0510-85919121; EMAIL: xiaws@jiangnan.edu.cnSearch for more papers by this authorQixing Jiang, Qixing Jiang State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 ChinaSearch for more papers by this authorYanshun Xu, Yanshun Xu State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Lihu 1800, Wuxi, 214122 ChinaSearch for more papers by this authorJing Fan, Jing Fan School of Liquor and Food Engineering, Guizhou University, Guiyang, ChinaSearch for more papers by this author First published: 27 February 2017 https://doi.org/10.1111/jfpp.13131Citations: 36Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract The effect of mixed starter cultures isolated from Suanyu on flavor compounds development has been researched. Microorganism, pH, TA, sugars, nonvolatile organic acids and volatile compounds were analyzed in Suanyu with or without starters. In inoculated samples, a higher growth of lactic acid bacteria (LAB) and a declining rate of pH were determined when compared with the controlled samples. Besides, higher levels of volatile compounds were detected in inoculated Suanyu (19342.47, 19852.74 × 106 area units for PS) than those in controlled samples. During the process, aldehydes, acids, alcohols, esters and ketones were formed and increased continuously. Especially in Suanyu with PS, higher levels of ethanol (6973.8, 6549.9 × 106 area units) and acetic acid (2116.8, 2471.1 × 106 area units) were detected, which could produce unique wine flavor and moderate acid taste. Furthermore, high content of hexanal was generated through the addition of PS, which could contribute to a green grass odor. Practical Applications In this study, microorganism, pH, TA, sugars, nonvolatile organic acids and volatile compounds were analyzed in Suanyu with autochthonous starter cultures. The results showed that the generative stability of Suanyu can be assured and the product quality can be advanced by adding autochthonous starter cultures compared with that of noninoculated samples. There is a need to add modern processing technology such as microbial fermentation of the fermentation process to achieve effective control to ensure product flavor and product quality stability. In this study, autochthonous starter cultures isolated from Suanyu, which were propitious to the demand of industrialization. Besides, once the research is applied in the industrialized production, and considerable social and economic benefits can be obtained. Therefore, this study has a good prospect in application. Citing Literature Volume41, Issue5October 2017e13131 RelatedInformation

Obscure pufferfish (Takifugu obscurus) softening during frozen storage remains to be solved. This study was therefore aimed to provide explanations by differentiate the roles of three potential factors in fish softening. The influences of ice crystal, endogenous proteolytic activities, and oxidization were distinguished by treatment of fish fillets with liquid nitrogen, iodoacetic acid, and tea polyphenol with ascorbic acid, respectively. This distinguishing method was verified to be effective by investigation in ice crystal microstructure, endogenous proteolytic activities and lipid and protein oxidation. In comparison of three factors, it showed that the shear force of fish fillets with smaller ice crystals was about 15.5% and 13.7% higher than those with the inhibition of endogenous proteolytic activities and oxidation respectively, indicating the dominant role of ice crystal in frozen fish softening. Besides, quality decline of frozen fish was initially fast and then slowed down during the storage.

Varisized chitosan-selenium (CS-Se) nanocomposites were synthesized through an innovative method. It is the first time to use CS both as reductant and stabilizer to synthesize selenium nanoparticles (SeNPs). By manipulating the temperature, the well-dispersed CS-Se nanocomposites were synthesized via a simple one pot reaction with the size ranging from 83 to 208 nm before being characterized by TEM, DLS, UV–vis, FTIR, XRD and TG analyses. The results showed that SeO32− was reduced to a stable SeNPs colloid at a comparatively high temperature, the amino group and hydroxyl group of CS were conjugated to the surface of SeNPs. Besides, the antioxidant activities of CS-Se nanocomposites were investigated by DPPH, ABTS+, hydroxyl radical, metal ion chelating and reducing power assays, which proved to be concentration-dependent, size-dependent and exhibited good antioxidant activities. The results suggested that CS-Se nanocomposites might be considered as a more appropriate selenium-adding form to achieve antioxidative goals in food.

The effects of a chitosan-based coating on the inhibition of microbial spoilage of grass carp (Ctenopharyngodon idellus) fillets were studied during refrigerated storage for 15 days in terms of pH, total volatile base nitrogen (TVB-N), trimethylamine (TMA), adenosine triphosphate (ATP)-related compounds, K value, microbial enumeration and high-throughput sequencing. The results indicated that the fillets treated with chitosan-based coating enriched with 0.3% glycerol monolaurate and 0.5% clove essential oil had lower values of TVB-N, TMA, hypoxanthine riboside (HxR), hypoxanthine (Hx) and K value with the significant reductions (P < 0.05) of nearly 34, 73, 32, 74 and 38%, respectively, when compared to the control at day 15 of storage. Using high-throughput sequencing analysis, the major bacteria phyla of Firmicutes, Cyanobacteria and Bacteroidetes and the bacteria family of Lachnospiraceae and Bacteroidaceae were observed in fresh grass carp. As storage time increased, the coated samples retained bacterial diversity. However, Shewanellaceae, Pseudomonadaceae and Flavobacteriaceae increased and became the predominant microbiota in spoiled control samples. The significant difference between the bacteria species in the control and coated samples showed that the coating had the potential to inhibit microbial growth, especially spoilage microorganisms, and reduced quality deterioration caused by bacteria during refrigerated storage of grass carp fillets.

The present study aims at synthesizing and in vitro antibacterial activity evaluation of chitosan oligosaccharide (COS) modified by Cinnamyl alcohol (Cin) onto the OH position of COS. Three different degrees of substitution (DS) COS-O-Cin1-3 were synthesized by changing different molar ratios of COS to Cin. UV–visible spectroscopy (UV–vis), Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (1H NMR), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and elemental analysis were conducted to characterize the successful synthesis of COS-O-Cin1-3. The results showed that they exhibited higher thermal stability, weaker crystallinity and better antibacterial properties than that of COS. These results aided in obtaining the important supports for exploring new functional antibacterial agents, which expand the scope of COS’s application in the food industry.

The effects of commercial starter cultures on the quality characteristics of fermented fish-chili paste were investigated. Five batches of fish-chili paste were prepared with different starter cultures, namely, SBM-52 (Staphylococcus xylosus, Staphylococcus carnosus, Pediococcus pentosaceus and Pediococcus lactis), PRO-MIX5 (Staphylococcus xylosus, Lactobacillus plantarum and Lactobacillus sakei), WBX-43 (Staphylococcus xylosus and Staphylococcus carnosus), V3 (Lactobacillus plantarum), and CO (spontaneous fermentation) as the control. The results showed that all the starter cultures accelerated the growth of lactic acid bacteria and obviously reduced the Enterobacteriaceae count compared with the CO batch. SBM-52, PRO-MIX5 and V3 quickly reduced the pH, and there was no obvious difference in the protease activities among these five batches (P > 0.05). The SBM-52 batch displayed a significantly higher level of total free amino acids than the control (P < 0.05). The accumulation of organic acids was mainly due to lactic acid in all the samples. Volatile analysis indicated that more ester compounds were detected in WBX-43 compared with the other samples. E-nose analysis showed an obvious difference in the overall odor among the different samples. In conclusion, the starter cultures of WBX-43 and SBM-52 could be used for the production of high-quality fish-chili paste with better flavor.

The effects of ice crystals, endogenous proteolysis and oxidization on flavor-related compounds of obscure pufferfish fillets during frozen storage were investigated in terms of biogenic amines, trimethylamine (TMA), free amino acids (FAA), nucleotides and electronic nose. These three factors were separately controlled by pretreatments of liquid nitrogen, iodoacetic acid and natural antioxidants, respectively. In general, the smaller ice crystals in fillets reduced accumulation of off-flavor compounds (such as hypoxanthine, TMA, lysine and putrescine), and increased umami-associated FAA and inosine monophosphate to a greater extend during storage when compared to other groups. According to the analysis of electronic nose and principal component analysis (PCA), the control pretreatments of endogenous proteolysis and oxidation were both beneficial to maintain the flavor quality of fillets, while the best preservation effect was observed in fillets frozen by liquid nitrogen, suggesting ice crystals played a more critical role causing the flavor loss of pufferfish during long-term frozen storage.

In this study, key aroma compounds of low-salt fermented sour fish were characterized using headspace solid-phase micro extraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS), odor activity values (OAV) and aroma recombination and omission experiments. Eighty-eight volatile compounds, including esters, aldehydes, alcohols, acids, furans and pyrazines, were identified by HS-SPME-GC-MS. Eighteen aroma-active compounds were quantified by employing calculation of OAV greater than 1. A recombination aroma model prepared using aroma-active compounds based on the odorless fish matrix sensorially matched the aroma of fermented sour fish with a score of 4.5 out of 5. The omission experiment showed that 7 out of 18 compounds had a significant contribution to the overall aroma (P < 0.05). The key aroma compounds of fermented sour fish were concluded to be ethyl acetate (OAV = 189), ethyl hexanoate (OAV = 66), isoamyl acetate (OAV = 424), ethyl butyrate (OAV = 26), hexanal (OAV = 49), 1-hexadecanal (OAV = 14) and 2-pentylfuran (OAV = 13).

The production of fish protein hydrolysates from bighead carp (Hypophthalmichthys nobilis) using ficin enzymes was achieved in optimal conditions of 3% enzyme/substrate ratio, 40 °C temperature, and pH 6. Three different hydrolysis times, 1, 3, and 6 h, were investigated, and their degree of hydrolysis (DH) values were 13.36%, 17.09%, and 20.15%, respectively. The hydrolysate yield values increased with DH increase, and the highest yield was obtained at DH 20.15%. The crude protein content increased from 80.58% to 85.27%, and amino acid compositions increased from 78.33% to 83.07%. The peptides formed during hydrolysis indicated low molecular weight that might improve functional characteristics of fish protein hydrolysates, including protein solubility, which ranged from 84.88% to 95.48% for all hydrolysates. The thermal degradation of hydrolysates occurred from 160 to 168 °C with intensive endothermic peaks. Results revealed that oil holding capacity was higher at DH 13.36%; water holding capacity was higher when DH increased. Hence, fish protein hydrolysates (FPH) from bighead carp have improved functional properties, and can be utilized as supplements and excellent protein sources in various uses in food applications.

Fish texture is important for consumers and degradation of myofibrillar structural proteins could cause softening. However, the role of endogenous proteases in degrading was not clear. In this study, protease inhibitors (Ac-DEVD-CHO, E−64 and EDTA-2Na) were used to distinguish the role of endogenous caspase-3, cathepsin B and L, and calpain. Results showed that caspase-3 and calpain had relatively high activity at initial ice-storage and decreased quickly afterwards, while cathepsins increased firstly and then fluctuated. Titin, nebulin and troponin-T were partially degraded by caspase-3 firstly. However subsequently, only titin and troponin-T were affected by cathepsins and calpain. Desmin showed a different degradation pattern. It was influenced by calpain significantly but not by caspase-3. Less than 2.5% of desmin remained after storage. Myofibril fragmentation index and shear force indicated that caspase-3-induced degradation occurred at initial ice-storage, while cathepsins had the greatest importance in texture softening during the whole storage.

The structural changes and aggregation properties of silver carp actomyosin acidified with d-gluconic acid-δ-lactone (GDL) were investigated. Results showed that silver carp actomyosin underwent aggregation and formation of precipitate as indicated by turbidity and centrifugation coupled electrophoresis analysis. Circular dichroism indicated that myosin rod unfolded during acidification, resulting in a gradual decrease in α-helical content. The changes in tertiary structure of actomyosin under acidic conditions were demonstrated by second-derivative UV spectra and intrinsic fluorescence. Tyrosine residues were exposed to the surface of proteins when pH was decreased to 5.5, and were buried inside the protein aggregates with further reduction in pH. In contrast, more tryptophan residues were exposed to the polar environment with decreasing pH. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide crosslinking experiments showed that the intensity of myosin heavy chain (MHC) bands decreased sharply with decreasing pH and the actin bands decreased more slowly, suggesting that MHC is the major protein component involved in the non-covalent cross-linking and formation of aggregates during acidification of silver carp actomyosin.

Silver carp (Hypophthalmichthys molitrix) is a popular cultured freshwater fish in China, and becomes a potential raw material for surimi product. However, silver carp surimi exhibits considerable gel softening (modori) and myofibril-bound serine proteinases (MBSP) involved in the degradation of myofibrillar proteins have been assumed to be crucial to the modori phenomenon. High-pressure technology has demonstrated its potential application to control enzyme-related seafood texture deterioration. Herefrom, it could be further applied to the freshwater fish processing and the effect of high pressure treatments on the activity of MBSP implicated in texture deterioration in myofibrils and crude enzyme extracts was evaluated. The inactivation kinetics of MBSP pressured from 200 MPa to 500 MPa at room temperature (20 °C) were fitted first-order kinetics, The extent of enzyme inactivation was lower in silver carp myofibrils in comparison with the crude enzyme extracts from myofibrils showing a protective effect against the high pressure treatment. The effect of HHP on MBSP myofibrillar degradation shown by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was associated with a corresponding decrease coincided with the elevated high pressure levels in intensity of myosin heavy chain (MHC). Dynamic rheological measurements indicated that high-pressure treatment exerted considerable influence on MBSP activities as well as proteins (mainly myofibrils), resulting in structural modifications and texture changes. In this study, 300 MPa (≥ 10 min) was the process condition (pressure and time) that caused apparent MBSP inactivation derived from the first order kinetic model and had the efficacy in controlling silver carp texture deterioration both verified by SDS-PAGE and dynamic rheological measurements.

A total of 21 Lactobacillus plantarum were isolated from a Chinese traditional low salt fermented whole fish product “Suan yu” and identified by biochemical and molecular methods. The isolates were screened for acidifying and amino-biogenic ability for proteolysis, lipolysis, antimicrobial activity, and sensory in order to select the most suitable candidates as the starter cultures. All the strains had high acidifying activities and were able to reduce the pH to lower than 4.5 in 36, 24 and 16 h at 15, 25 and 37 °C respectively. Major strains showed antimicrobial activities against Listeria monocytogenes, Staphylococcus aureus and Escherichia coli, and ten L. plantarum strains could produce bacteriocins. Five L. plantarum strains exhibited weak proteolytic activities against myofibrillar proteins, as evidenced by the agar plate assay and sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE). None of the strains showed lipolytic activity. Major L. plantarum strains displayed different enzymatic profiles. Besides, the isolates mostly showed negative-decarboxylase activities, but Lp-10 had a decarboxylase activity against l-tyrosine. Furthermore, the fermented fish surimi inoculated with Lp-15 and Lp-21 strains respectively scored high for overall acceptability. Therefore, Lp-15 and Lp-21 presented the best technological properties, which should be given first priority as the starter culture for manufacturing fermented fish products.

Proteolytic changes in Suanyu, a traditional fermented fish product of China, were determined during 6 weeks of fermentation. The gradual decrease of pH value and aw was detected, accompanied with an increasing trend detected in trichloroacetic acid–soluble C-1: peptides concentration. Protein composition changed throughout the fermentation. A decrease in sarcoplasmic and myofibrillar protein fractions was accompanied by an increase in the insoluble fraction. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed most bands of sarcoplasmic, myofibrillar, and insoluble proteins lightened or disappeared due to proteolysis or denaturation. New bands emerged especially in insoluble proteins. Fluctuation of molecular weight distribution of the water-soluble nitrogen in Suanyu was found during fermentation. The highest percentage in Suanyu end-products was observed in the fraction of <0.18 kDa, followed by 0.18–0.5 kDa, 66.02 ± 0.38% and 10.79 ± 0.27%, respectively. Free amino acids analysis showed that nearly all amino acids increased, especially for Asp, Glu, Met, Phe, Leu, Val, and Ile. Overall, intense proteolysis in Suanyu brought numerous of small peptides and free amino acids, which contribute to the taste and flavor of Suanyu.

The aim of this study was to investigate endogenous proteolytic activities in a cod product and their impact on muscle proteins and textural properties during fermentation and storage. The result of specific proteolytic activities showed that cathepsins, especially cathepsin B, had the highest activities during fermentation and storage. SDS-PAGE indicated more degradation of myofibrillar proteins by cathepsin L than other proteases and that the hydrolysis by cathepsins was pronounced in the last stage of fermentation. Texture analysis showed that cathepsins had a negative impact on gel strength and this impact increased in the last stage of fermentation. However the product still had a firm texture. During storage (4 °C) for one week, no significant changes were seen in the gel strength. In conclusion, cathepsins had more impact on muscle proteins and textural properties than other proteases during fermentation but had little impact on gel strength during storage at 4 °C.

Summary The objective of this study was to investigate the effect of mixed kojis on essential indices of fish sauce. Fish sauce inoculated with mixed kojis ( FSB , Aspergillus oryzae koji: Aspergillus niger koji = 3:1) and A. oryzae koji ( FSA , control) was prepared. At the end of fermentation, the content of amino nitrogen, total soluble nitrogen, Free amino acid (FAA) and glutamic acid in FSB increased by 7.50%, 7.84%, 9.80% and 28.43% compared to FSA , due to higher acid protease activity in mixed kojis. Moreover, flavour groups including phenols, ketones and nitrogen‐containing compounds in FSB were also improved. According to the results of sensory evaluation, FSB showed higher intensity of umami and caramel attributes, lower intensity of ammonia and sour attributes. All the results suggested that the usage of mixed kojis to produce fish sauce was an effective method that can accelerate the fermentation process and improve the flavour of fish sauce made with freshwater fish by‐products.

This study investigated the effects of Lactobacillus plantarum 120, Saccharomyces cerevisiae 2018 and Staphylococcus xylosus 135 inoculation on N-nitrosodimethylamine (NDMA) and its precursors formation, and on microbiological characteristics of Chinese traditional fermented fish products (CTFPs). The results indicated that three strains could directly degrade NDMA in culture broth, and the highest degradation rate was observed in L. plantarum 120. The lactic acid bacteria counts in samples inoculated with L. plantarum 120 and mixed starter cultures were significantly (P < 0.05) higher than the others during the initial and middle fermentation stages (≤3 weeks). The final contents of total volatile base nitrogen, trimethylamine, dimethylamine, nitrite and NDMA in inoculated samples were significantly (P < 0.05) lower than those in spontaneous fermentation samples. According to these results, the inoculation with autochthonous starter cultures was a promising method to inhibit the NDMA and its precursors accumulation in CTFPs during fermentation process.

Summary Effects of chitosan coating combined with essential oils from clove, cinnamon and lemon grass on quality and antioxidant enzyme activities of grass carp fillets stored at 4 ± 0.5 °C were evaluated. The quality parameters (including pH , total volatile basic nitrogen ( TVB ‐N), K value, thiobarbituric acid ( TBA ) value, shear force and total viable count ( TVC )) and antioxidant enzyme activities were analysed periodically. The results indicated that composite chitosan coatings presented better preservation effects than chitosan coating alone. In addition, chitosan–clove essential oil coating had the best quality enhancement effects among treatments by inhibiting deterioration of physicochemical quality and microbial growth and maintaining antioxidant enzyme activities of fillets during refrigerated storage. The negative correlation was observed between the changes in TBA values and antioxidant enzyme activities in fillets. Based on these findings, chitosan–essential oil coatings effectively mitigated oxidative stress and extended shelf life of refrigerated grass carp fillets.

The effect of heating temperature and duration on the texture and protein composition of bighead carp (Aristichthys nobilis) muscle was investigated. Samples were heated at 90°C, 100°C, 110°C, and 120°C for different times. The results showed that cooking loss increased significantly with increasing temperature and heating time, and a fractional conversion model was used to describe the increase. Hardness, chewiness, and gumminess exhibited a similar four-phase change with two peaks at 90°C, 100°C, and 110°C, and the trend was not observed at 120°C. Analysis of sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) revealed that contents of myosin heavy chain decreased entirely to disappear and contents of actin significantly decreased. Increasing the intensity of the heavy molecular weight bands indicated the aggregation of myosin. Content of water-soluble proteins presented an increasing trend, which reflected the protein degradation and the release of low-molecular-weight compounds.

The impact of immersion freezing (IF) with edible solution (ethanol, NaCl, dextran, active protein, chrysin and naringenin) on physical properties of obscure pufferfish (Takifugu Obscurus) was compared with air freezing (AF) and liquid nitrogen freezing (LNF). Freezing process, microstructure, texture characteristics, water holding capacity, and cell integrity were investigated. Results showed that IF(-30 °C) rate was 11.5/4.7-fold quicker than AF(-18/-50 °C) rate. As for microstructure, ice crystals in IF(-30 °C) fish were much smaller than that in AF. Referring to texture characteristics and water holding capacity, shear force and hardness of IF(-30 °C) fish were 12.9% and 16.7% higher, and drip and cooking loss were 44.1% and 8% lower, than that of AF(-50 °C) fish after 24 weeks storage. Besides, IF led to higher integrity of muscle fibers than AF. For all physical indexes, IF fish had similar quality as LNF fish. Principal component analysis (PCA) further proved these results. In conclusion, edible IF(-30 °C) could retard physical properties deterioration of frozen fish in a better way than AF and have potential to replace LNF.

Spherical lignin nanoparticles (LNPs) offer more possibilities for high value-added use of lignin, but un-ecofriendly organic solvents used for preparing LNPs must be addressed. This study reported a green and simple method to produce LNPs using a betaine:lactic acid deep eutectic solvent (DES) via self-assembly induced by dropping water. The critical water content (41 vol%) at the beginning of self-assembly was determined by dynamic light scattering. The well-defined spherical colloid particles with an average size of 57.16 ± 1.43 nm were obtained after adding 80 vol% water content, followed by verifying the morphologies via scanning electron microscopy and transmission electron microscopy. A better water dispersibility of colloid particles was elucidated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The stable LNPs were optimized at 5 mg/mL of initial lignin concentration, 1 mL/min of dropping speed, and 80 vol% water content. Compared with lignin, LNPs exhibited improved thermal stability, enhanced antioxidant activity, and lower minimum inhibitory concentration against Staphylococcus aureus (4.0 mg/mL). Further, 7.5 mg/mL of LNPs concentration demonstrated its potentiality as a stabilizer in Pickering emulsions. Furthermore, the produced LNPs displayed high potential in bio-based materials and emulsion, providing a critical foundation for broadening the further utilization of lignin.

In the current study, bighead carp fish were used in conjunction with the flavourzyme enzyme to obtain (FPH) fish protein hydrolysates. The optimum conditions of the hydrolysis process included an enzyme/substrate ratio of 4% and a temperature of 50 °C and pH of 6.5. The hydrolysis time was studied and investigated at 1, 3, and 6 h, and the (DH) degree of hydrolysis was recorded at 16.56%, 22.23%, and 25.48%, respectively. The greatest yield value was 17.83% at DH 25.48%. By increasing the DH up to 25.48%, the crude protein and total amino acid composition of the hydrolysate were 88.19% and 86.03%, respectively. Moreover, more peptides with low molecular weight were formed during hydrolysis, which could enhance the functional properties of FPH, particularly the solubility property ranging from 85% to 97%. FTIR analysis revealed that enzymatic hydrolysis impacted the protein's secondary structure, as indicated by a remarkable wavelength of amide bands. Additionally, antioxidant activities were investigated and showed high activity of DDPH radical scavenging, and hydroxyl radical scavenging demonstrated remarkable activity. The current findings demonstrate that the functional, structural, and antioxidant characteristics of FPH might make it an excellent source of protein and suggest potential applications in the food industry.

The quality of freshwater fish is easy to deteriorate during postmortem storage, so it is necessary to find an effective method to extend the shelf life of fish fillets. The aim of this study is mainly to develop a novel bilayer active film with curcumin/nisin-loaded pectin nanoparticles (CZ-NPs) and evaluate its effect on the quality of fish fillets. The selected sensory, physicochemical (pH, color qualities, TVB-N, TBARS, biogenic amines, moisture state) and microbial properties (microbial enumeration and high-throughput sequencing) were analyzed to confirm the preservative mechanism of films on the fillets. During storage at 4 °C, better sensory evaluation feedback and lower total volatile base nitrogen in the film treated samples was observed when compared to the control samples. Additionally, CZ-NPs film effectively inhibited oxidation, with the final reductions of 1.04 mg MDA/kg flesh when compared to control. As suggested by low-field NMR and magnetic resonance imaging, film treated fillets presented higher water holding capacity by controlling transformation from immobilized to free water. Meanwhile, lower microbial enumerations were also recorded in the CZ-NPs film treated group, which was reduced by a range of 1.8–2.3 log CFU/g on day 10 when compared to control. High-throughput sequencing results showed that the Pseudomonas constituted the main spoilage bacteria of fillets, and CZ-NPs film contributed to the notably suppressed growth of Pseudomonas. As a result, CZ-NPs film showed a desirable application to extend the shelf life of refrigerated flesh, as an alternative for fishery product packaging and preservation.

Herein, the protective pattern of chitosan coating enriched with green tea extract on texture stabilization of refrigerated grass carp fillets was explored. In general, higher shear force and lower endogenous enzyme activities were observed in coated fillets, with the max. level of cathepsins and calpain decreasing by 30.2 ∼ 39.6 % when compared to the control during storage. Meanwhile, the coating reduced protein composition changes and accumulation of protein degradation products. According to label-free proteomic analysis, the proteome closer to fresh sample was observed in coated fillets than that of the control, as supported by PCA and hierarchical cluster analysis. Meanwhile, 33 differential proteins involved in tissue structure, protein phosphorylation and protein turnover were further screened out, and most DAPs showed up-regulation in coated fillets compared to the control on day 12. Presumably, the coating modulated endogenous enzyme-induced myofibrillar protein degradation and protein phosphorylation level, thereby stabilizing the texture properties of refrigerated fillets.

Herein, the protective pattern of bilayer film on the texture stability of fillets was discussed in terms of endogenous enzyme activity, as well as protein oxidation and degradation. The texture properties of fillets wrapped with nanoparticles (NPs) bilayer film were greatly improved. NPs film delayed protein oxidation by inhibiting the formation of disulfide bond and carbonyl group as evidenced by the increase of α-helix ratio (43.02%) and the decrease of random coil ratio (15.87%). The protein degradation degree of fillets treated with NPs film was lower than that of control group, specifically with a more regular protein structure. The exudates accelerated the degradation of protein, while NPs film effectively absorbed exudates to delay protein degradation. Overall, the active agents in the film were released into the fillets to play an antioxidant and antibacterial roles, and the inner layer of film could absorb exudates, thus maintaining the texture characteristics of fillets.

Despite extensive commercial and regulatory interventions, food spoilage and plastic packaging contamination continue to have large ramifications on human health and the global economy. Intelligent active packaging that can both monitor food freshness in real-time and improve food quality is needed. In this study, curcumin-zein- quercetin-chondroitin sulfate nanoparticles (CZQC NPs) with ammonia/acetic acid sensitivity and antioxidant activity were prepared and then loaded within a chitosan film to give a smart film. The effect of NPs loading upon the structure and physicochemical characteristics of the chitosan based films were studied. The scanning electron microscopy confirmed that the NPs had good compatibility with chitosan and filled the void in the film matrix. The NPs were uniformly integrated inside the chitosan film, which significantly improved its mechanical properties (tensile strength from 26 to 62 MPa; elongation at break from 35 to 61%), oxygen and water barriers and ultraviolet light protection. The NPs films showed significant antibacterial efficacy, antioxidant activity and a beneficial ammonia/acetic acid/pH-sensitivity. Thus, the NPs composite film could sensitively detect fillets freshness with discernible color changes. Therefore, the NPs composite films may potentially be applied to indicate and extend the freshness of packaged foods.

Consumers are greatly concerned about fish freshness. Therefore, this study was aimed to provide a colloidal gold immunochromatography assay (GICA) system for rapid detection of fish freshness. A suitable fish protein was chosen as an antigen for GICA; and the properties and effectiveness of the GICA system were investigated. Results showed that parvalbumin (PV) was suitable as a fish freshness indicator, proven by hierarchical cluster analysis and chosen as a GICA antigen. The GICA system revealed high specificity in the 27–212 μg/L detection range. The correlation coefficient R2 towards enzyme-linked immunosorbent assay reflected high reliability as 0.998. The GICA system was stable within 12 weeks at room temperature. The fitness for indicating freshness by GICA ranged from 87.27% to 111.72%. In short, the GICA system with PV as an antigen could be used as a simple, rapid, and accurate technique for the freshness detection of grass carp fillets.

Our work here, for the first time, reported the antibacterial activity of kojic acid-grafted-chitosan oligosaccharides (COS/KA) against three gram-positive and three gram-negative bacteria. Integrity of cell membrane, outer membrane (OM) and inner membrane (IM) permeabilization assay, alkaline phosphatase (ALP) and glucose-6-phosphate dehydrogenase (G6PDH) assay, and SDS-PAGE assay techniques were used to investigate the interactions between COS/KA and bacterial membranes. The antibacterial activity of COS/KA was higher than those of unmodified COS. The electric conductivity of bacteria suspensions increased, followed by increasing of the units of average release for ALP and G6PDH. COS/KA can also rapidly increase the 1-N-phenylanphthylamine (NPN) uptake and the release of β-galactosidase via increasing the permeability of OM and IM in Escherichia coli. SDS-PAGE indicated the content of cellular soluble proteins decreased significantly in COS/KA-treated bacteria. Hence, COS/KA has potential in food industry and biomedical sciences.

Summary The aim of this study was to investigate the lipolysis and lipid oxidation of Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31 in Suan yu. Suan yu were made inoculated with and without two strains at different stages, and model systems of emulsions were also established. Lipolysis and lipid oxidation were evaluated by determining the changes in free fatty acid ( FFA ) content and composition, conjugated diene ( CD ) value and thiobarbituric acid reactive substances ( TBARS ) value. The total FFA of the sample without cultures increased from 476.61 mg/100 g fat to 1413.89 mg/100 g fat after 5 weeks fermentation, while those of samples with cultures declined to 258.98 and 452.89 mg/100 g fat, respectively. On the other hand , CD and TBARS values of samples with inoculation markedly increased. In the model system, higher FFA , CD and TBARS values for the samples added with CFE were observed. This study showed that Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31 made a significant contribution to lipolysis and lipid oxidation during the processing of Suan yu.

This study investigated the effect of chitosan coating (1 and 2%) on the quality of grass carp fillets stored at 4°C for 20 days. During storage, the physicochemical properties (pH, thiobarbituric acid value, total volatile basic nitrogen value, trimethylamine nitrogen value, K-value, water loss, and instrumental texture), microbiology (total viable count and psychrotrophic count), and sensory properties were evaluated. The results showed that chitosan coating could effectively inhibit bacterial growth, improve physicochemical and sensory qualities, and it reduced the deterioration of the quality of grass carp fillets. Compared with fillets without chitosan coating, the shelf life of fillets with 1 and 2% chitosan coating was extended by ~3 and 6–7 days, respectively.

Abstract BACKGROUND Texture deterioration often negatively affects sensory attributes and commercial values of ice‐stored fish fillets. The mechanism of softening of fish fillets during chilling storage is not fully resolved. Grass carp is a predominant freshwater fish species in China. The objective of the present study was to investigate the differential role of endogenous cathepsin and microorganisms in texture softening of ice‐stored grass carp fillets. RESULTS The fillets were immersed in either NaN 3 solution to reduce microbial activity or in iodoacetic acid solution to exclude cathepsin activity before ice storage. Treatment with NaN 3 reduced microbial load of fillets below 2 log CFU g −1 muscle during the entire storage period, and had no significant influence on the cathepsin activity and proteolysis. But the shear force of fillets treated with NaN 3 decreased by 66% after 21 days of storage. Meanwhile, treatment with iodoacetic acid inactivated cathepsin B and B + L but did not significantly affect the microbial growth of fillets. Compared to NaN 3 treatment, iodoacetic acid effectively alleviated softening and inhibited the increase in TCA ‐soluble peptides during storage. CONCLUSION This study demonstrated that proteolysis induced by endogenous cathepsins, rather than microorganisms, plays an important role in texture softening of ice‐stored grass carp fillets. © 2015 Society of Chemical Industry

Summary The objective of this work was to analyse the role of desmin in texture softening and water‐holding capacity ( WHC ) of ice‐stored grass carp fillet. Results indicated that shear force of the fillet decreased sharply within 3 days, while drip loss increased during the whole ice storage. Water mobility and distribution were measured by low‐field 1 H NMR T 2 relaxation that revealed a positive correlation ( P &lt; 0.01) between WHC and the mobility of the immobilised water (T 21 relaxation time). Meanwhile, negative correlation could be established between intact desmin and drip loss ( P &lt; 0.01). Intact desmin was extremely correlated with shear force ( P &lt; 0.01) and positively correlated with calpains activity ( P &lt; 0.05). This study demonstrated that the degradation of desmin was involved in the mobility of the myofibrillar water and softening of grass carp fillet during ice storage. Furthermore, calpains autolysis seemed to result in desmin degradation.

The study was aimed to investigate different roles of endogenous and Lactobacillus plantarum proteases during fast fermentation of silver carp. The results show that endogenous proteases could degrade both sarcoplasmic and myofibrillar proteins. In contrast, L. plantarum had low proteinase activities and could only hydrolyze sarcoplasmic peptides. This indicates that gel properties could be mainly affected by endogenous proteolysis while microbial proteolysis contributed to the production of smaller peptides and free amino acids which may be related to flavor and taste. Texture and free amino acid analyses verified these hypotheses. It shows that endogenous lysosomal proteases were the major contributors for the decrease of gel strength while L. plantarum proteolytic activities could lead to the increase of aspartic acid, glutamic acid, and alanine, which may result in umami and sweet taste; and also lead to a rise in some amino acids which were volatile compounds precursors.

The purpose of this work was to develop a nontoxic bioactive material based on a natural pyrone compound (kojic acid, KA) and chitosan oligosaccharides (COS). The bioactive material, chitosan oligosaccharide-N-kojic acid polymer (COS-N-KA), was prepared by one-step environmentally friendly approach. Then, the physicochemical properties and biological activities of COS-N-KA as a prepared water-soluble COS derivative were evaluated. The polymer was characterized by using UV–vis, FTIR, 1H NMR, and 13C NMR spectroscopy, Mw, PID, TGA, water solubility, hemolysis assay, and animal toxicity studies. Particularly, the antioxidant and antimicrobial assays revealed that COS-N-KA significantly enhanced the antimicrobial and antioxidant activities, which remarkably stronger than that of free COS and KA. Hence, the low hemolytic activity to human red blood cells, and nontoxic to female mice of SLAC KM strain made this novel polymer material a promising and effective compound for food and pharmaceutical industries.

Protein hydrolysates from Chinese sturgeon were prepared using Alcalase 2.4L enzyme. Under the optimum conditions (enzyme–substrate ratio of 3.5%, pH of 8.5, and temperature of 55°C), the degree of hydrolysis (DH) was 13.8%, 16.7%, and 19.1% after 1, 3, and 6 h, respectively. The contents of crude protein and amino acid increased at DH of 19.1% to 86.97% and 78.29%, respectively. There was an obvious increase in the low-molecular-weight peptides, which could enhance the hydrolysate’s functional properties such as solubility, representing more than 90% at different pH levels. The obtained protein hydrolysates revealed good emulsification properties and high oil absorption. Furthermore, good antioxidant activities such as 1, 1-diphenyl-2-picrylhydrazyl (DPPH) inhibition, ferric reducing power, and ferrous ion (Fe2+) chelating ability were attained depending on the solution concentration. The findings indicate that the functional and antioxidant properties of protein hydrolysates could be useful in many applications of the food industry.

The effects of cold air drying (CD) and hot air drying (HD) on the physical properties and protein stability of slightly salted silver carp fillets were investigated in terms of water-related indicators, texture profile, color and protein denaturation analysis. The results indicated moisture content of fillets exponentially decreased to 1.19 and 1.07 g water/g drying matter at the end of drying, respectively, accompanied with the decreases in water activity, and water mobility based on the results of leftward shifted T21 and T22 relaxation time. The gradual increase of hardness and chewiness, and decrease of adhesiveness of dried fillets were observed in both groups during the drying process. By contrast, CD made fillets with higher hardness and chewiness properties when compared to HD under similar moisture content. The more intense browning reaction was observed in hot air dried fillets, reflecting by the sharp increase of b* value (p < 0.05) from the initial 1.25 to final 13.44. Besides, the results of protein-related indicators showed HD easily resulted in protein aggregation and secondary structure degradation. Summarily, this study revealed the change characteristics of salted silver carp fillets during two conventional air dryings, providing a basis to further propose reasonable combination drying programs.

Chinese mitten crab (Eriocheir sinensis) needs sensory evaluation for grading. This study compared data mining (DM) and sensory panel evaluation (SPE), using data visualization (DV) and quantitative descriptive analysis (QDA), respectively. Results showed that Yangcheng Lake Crab (YLC) was the most welcomed for “umami” and “sweet” according to DV; and QDA (7-scale) showed similar results of the highest “aroma-sweet” (Average Score 4.5) and “taste-umami” (Average Score 4.6) in YLC. The difference was that, DV was fast based on big data (1.4 million words); while QDA quantified detailed attributes (principle components > 85.3% averagely) based on highly-trained sensory panel of good distinguishing- and repeating- ability that F value showed 76.4% of all attributes > 5% for panelist averagely, and mean square error < 0.500 except one panelist. In conclusion, DM was quick but qualitative; while SPE was laborious but informative.

Postmortem alteration by apoptosis has significant effects on flesh quality. Currently, the information necessary to understand the apoptotic behavior and the molecular mechanisms during postmortem alteration in fish muscle is still lacking. Activation of apoptosis and the cytokines involved in regulating apoptosis in fish muscle were evaluated during postmortem condition at 4 °C for 5 days in terms of apoptotic morphology changes, nucleus DNA fragmentation, caspases activation and related gene expressions. The triggering apoptotic mechanisms associated with multiple cytokines transcriptional levels showed that the up-regulated pro-apoptotic mediators [IFN-γ2, TNF-α, IL-6, IL-1β, IL-17D, IL-12p35 and IL-10 (except IL-15)] and the down-regulated anti-apoptotic mediators of [IL-8 and IL-11 (except TGF-β and IL-4)] both regulated apoptosis at early stage, which were regulated by NF-κB and TOR, respectively. Results suggested that transcriptional regulation of multiple cytokines produce a positive outcome on triggering apoptosis.

The effects of different content of sodium chloride (NaCl) and sodium pyrophosphate (SPP) on the stability of myofibrillar proteins (MPs) sol subjected to freeze-thaw cycles (F-T cycles), as well as the performance of heat-induced gel subsequently formed from the frozen-thawed MPs sol, were investigated. The molecular states of MPs with high NaCl (15 g/kg, 25 g/kg) and additional SPP (1 g/kg, 3 g/kg, 5 g/kg) were altered due to the cross-linking and aggregation, showing the larger turbidity, higher surface hydrophobicity, and intrinsic fluorescence intensity. Additionally, compared with the control and 5 g/kg NaCl groups, MPs sol with high NaCl content exhibited less proteins denaturation and higher stability of water molecules after 2 F-T cycles. However, the poor gel properties were observed in high NaCl groups with larger cooking loss, weak gel strength, inferior textural parameters, and disorganized micro-network structure, revealing cross-linking and aggregation of MPs during F-T cycles were negative to the gelling properties. Furthermore, the additional SPP (1 g/kg) significantly inhibited protein aggregation and water migration during F-T cycles of MPs sol, resulting in superior gel properties with ordered gel microstructures.

Summary In this study, two groups of mixed starter cultures ( S 1, S 2), which were isolated from S uan yu, were inoculated for this experimental product, and a batch without starters was used as the control. The effect of the mixed starter cultures on the suppression of biogenic amine ( BA ) produced during the ripening of S uan yu was investigated. Changes in BA , p H , total volatile base nitrogen ( TVB‐N ), microbial counts and free amino acids ( FAA ) contents were detected during ripening. The results show that the mixed starter cultures rapidly decreased p H , inhibited the growth of contaminant microorganisms emerged in the sample and drastically reduced the accumulations of tyramine, putrescine and cadaverine. However, histamine and spermine were not produced in any batch. Besides, p H , FAA and BA production were not directly correlated. The study suggests that inoculation with S 1 and S 2 inhibited BA , thereby improving the product safety.

The hypolipidemic activities of high and low molecular weights of chitosan nanopowders (HMW-chitosan-NP: 315 kDa; LMW-chitosan-NP: 51 kDa) prepared by ultrafine milling were evaluated in rats. The results showed that the hypolipidemic activity of chitosan nanopowder was better than ordinary chitosan, and LMW-chitosan-NP was superior to HMW-chitosan-NP in hypolipidimic activity. Compared with ordinary chitosan, chitosan nanopowder increased the fecal lipids and the activities of serum and liver lipoprotein lipase (LPL) and hepatic lipase (HL) of rats. Rats receiving LMW-chitosan-NP excreted less lipids in feces, but showed higher serum and liver LPL and HL activities compared with those fed HMW-chitosan-NP. These results suggested that compared with ordinary chitosan, the increased hypolipidemic activity of chitosan nanopowder might be attributed to its ability on increasing fecal lipid excretions and stimulating LPL and HL activities, and the better stimulation of LMW-chitosan-NP in activities of these lipases might help it to exceed HMW-chitosan-NP in hypolipidemic activity.

The objective of this study was to investigate the differential role of cathepsin B, L, D and calpain in degradation and disassembly of myofilament. Myofibrillar protein of grass carp (Ctenopharyngodon idella) was incubated with proteases monotonously, simultaneously or sequentially. Subsequently, protein degradation were detected using SDS-PAGE and myofilament disassembly induced by changes of non-covalent interactions were measured through SDS-PAGE using l-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide (EDC) as a zero length cross-linker. Additionally, content of heat shock proteins which functioned in stabilizing assembly architecture of myofibrillar protein was determined. Results showed that calpain and cathepsin B, calpain and cathepisn L could act in a stepwise and complimentary manner to synergistically dissociate and degrade myofibrillar protein. In synergistic action, cathepsin B disrupted the thick filament assembly through lowering the UNC45 and HSP90 concentration in myofibrillar protein, facilitating the degradation of dissociated MHC by calpain. Meanwhile, Cathepsin L was shown to preferentially remove the actin from thin filament via lowering the content of HSP27 and αb-crystallin, to create dissociated actin as substrate supply for calpain.

N,O-Carbonylated chitosan derivative (NTCS) was synthesized via oxidation and substitution reaction, respectively. The carboxyethylation of the polysaccharide was identified by Fourier transform infrared (FTIR), 1H nuclear magnetic resonance (NMR), X-ray diffraction analysis (XRD), Zeta potential measurement and Thermogravimetric analysis (TGA). It is revealed that compared with chitosan (CS), NTCS exhibited an excellent solubility in distilled water, high in vitro bile acid binding capacity, as well as a low viscosity. The in vitro bile acid binding capacity reached 17.21 mg/g, which was 4.5-fold higher than that of CS. The results suggest that NTCS may be useful as a potential functional food supplement in food industry or a key ingredient in the pharmaceutical industry. These findings provide important supports for developing new food additive, and expand the scope of application of CS in the food industry.

The influence of simultaneous combination of microwave and steam cooking on contents of specific phytochemicals, carbohydrate and antioxidant activity of purple sweet potatoes (PSPs) was investigated, and compared to those of individual steaming and microwaving. Results showed that the contents of phytochemicals including total phenolics, flavonoids and anthocyanins and phenolic acids except caffeic acid increased after cooking to different extent depending on cooking methods. The PSPs cooked by simultaneous combination of microwave (500 W) and steam (1700 W) for 12 min (M500-S1700-12) contained the highest of total phenolics, flavonoids, phenolic acids and anthocyanins. Simultaneous combination of microwave and steaming resulted in higher content of soluble sugar in PSPs. PSPs cooked by M500-S1700-12 showed the highest antioxidant activity, which was well accordance with higher contents of phytochemicals. The findings suggest that appropriate simultaneous combination of microwave and steaming could better preserve active phytochemicals in PSPs, but significantly shorten cooking time compared with individual steaming. Simultaneous combination of microwave and steam cooking is a new technology for cooking food. However, the information about the effects of simultaneous combination of microwave and steam cooking on quality of food is limited. The present findings showed that the appropriate combination of microwave and steam cooking could significantly decrease the cooking time and improve nutrition value of cooked PSPs. This research is not only of importance for understanding the changes of food composition during different heating process, but also has important practical significance for choosing a scientific cooking methods and developing new type of cooking utensils which can better satisfy current consumers' needs.

Transcriptome analysis was performed to investigate the alterations in gene expression after chitosan (CS) treatment on the liver of mice fed with high-fat diet (HFD). The results showed that the body weight, the liver weight and the epididymal fat mass of HFD mice, which were 62.98%, 46.51% and 239.37%, respectively, higher than those of control mice, could be significantly decreased by chitosan supplementation. Also, high-fat diet increased both plasma lipid and liver lipid as compared with the control mice. Chitosan supplementation decreased the plasma lipid and liver lipid, increased the lipoprotein lipase (LPL) and hepatic lipase (HL) activity, increased T-AOC and decreased MDA in the liver and the epididymis adipose as compared with the HFD mice. Transcriptome analysis indicated that increased Mups, Lcn2, Gstm3 and CYP2E1 expressions clearly indicated HFD induced lipid metabolism disorder and oxidative damage. Especially, chitosan treatment decreased the Mup17 and Lcn2 expressions by 64.32% and 82.43% respectively as compared with those of HFD mice. These results indicated that chitosan possess the ability to improve the impairment of lipid metabolism as strongly associated with increased Mups expressions and gene expressions related to oxidative stress.

The objective of this work was to investigate the effects of sodium replacement on the textural properties and water-holding capacity (WHC) of heat-set freshwater surimi gels. Potassium chloride and calcium chloride were chosen as salt substitutes. The surimi gels presented better water-holding capacity with potassium chloride than the treatments containing calcium chloride. Gel strength and rheological properties indicated that monovalent metal ions could improve surimi gel properties. The contents of chemical interactions, especially disulfide bonds, nondisulfide covalent bonds, and hydrophobic interactions of surimi gels, varied with the addition of salt type and concentration. Furthermore, microstructure observed from scanning electronic microscopy (SEM) demonstrated that surimi gels prepared with monovalent salt presented more compact and denser networks, while more aggregated particles existed in gels with calcium chloride.

Biosynthesis of acetate esters by Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31, isolated from Chinese traditional fermented fish (Suan yu) were studied. A buffer system containing acyl donors (acetic acid/glyceryl triacetate/acetyl-CoA) and aliphatic alcohols (C2-C6) was established, inoculated with intracellular and extracellular extracts of the three strains. The results showed that the biosynthesis pathway of L. plantarum 120 was esterification and alcoholysis, while the biosynthesis pathway of S. xylosus 135 and S. cerevisiae 31 was hydrolysis and esterification, rather than alcoholysis. The ester-synthesizing activity of L. plantarum 120 via alcoholysis was higher than that via esterification at high pH value, while an opposite result for each strain was observed at low pH value. Moreover, the ester-synthesis activity of L. plantarum 120 was higher than that of S. xylosus 135 and S. cerevisiae 31. In addition, microbial ester-synthesis activity increased with the increase of aliphatic alcohol carbon number.

In this study, the aroma volatile compounds of commercial Chinese traditional fermented fish (Suan yu) from western Hunan were investigated. A total of 59 volatile compounds were identified and quantified by GC-MS combined with headspace solid-phase microextraction. Esters and alcohols presented over 50 percent of the overall aroma in concentration. With the calculation of odor activity values (OAVs), 20 odorants were recognized as aroma-active compounds due to their OAVs greater than 1, including esters (10), alcohols (5), acids (1), and aldehydes (4). Sensory evaluation revealed higher scores in estery, fruity, and grassy attributes than others. A positive correlation between sensory attributes and aroma-active compounds was clearly elaborated by partial least squares regression analysis (PLSR). PLSR results indicated that ethyl-2-methylbutyrate, ethyl 3-methylbutyrate, and ethyl decanoate were significantly and positively correlated with fruity attribute, while ethyl hexanoate and 1-octen-3-ol had a significant positive impact on estery and grassy attribute, respectively. This study elaborates the aroma profile of Suan yu from western Hunan of China, and implies the availability of PLSR for the flavor evaluation of fish products.

To investigate the underlying mechanism of softening of ice-stored grass carp fillet, changes in assembly structure of myofibrillar proteins and potential candidates for regulating this change including myosin regulatory chain phosphorylation, heat shock proteins (Hsp27, Hsp90, αB-crystallin and UNC45) and endogenous protease activity were studied. Comparison of SDS-PAGE pattern of myofibrillar proteins treated with EDC crosslinking showed that thin filament experienced rapid disassembly within initial 8 h, followed by depolymerization of thick filament consisting of myosin, which further exacerbated the myofibril disorganization of fillets. Pearson coefficient analysis showed that UNC45, Hsp90, Hsp27 and αB-crystallin concentration and cathepsin B, D, L activities were significantly correlated with dissociated MHC and actin. Therefore, the significant correlation between shear force and dissociated MHC and actin clearly demonstrated that post mortem disassembly of myofibril filaments, which was regulated by endogenous proteolytic activity and loss of Hsp, contributed to the softening of ice-stored grass carp fillets.

Degree of hydrolysis (DH), yield, amino acid profile, protein solubility, and antioxidant activity of Chinese sturgeon protein hydrolysates, as influenced by thermal pretreatment, ultrasonic (US), microwave (MW), and combined US-microwave pretreatments were investigated. Initially, the samples were subjected to thermal pretreatments in order to measure their effect on DH, which increased at 55°C. The DH recorded 7.63, 5.55, and 6.02% for US, MW, and combined US-MW pretreatment (US + MW), respectively, at the optimal time (8 min). The enzymatic hydrolysis (EN) of pretreated samples increased the DH to 19.41, 14.18, and 16.91% for US + EN, MW + EN, and US + MW + EN, respectively. The US + EN treatment was most effective for obtaining higher DH and yield, which were 19.41% and 18.62%, respectively. The use of US + EN also resulted in an increase in the percentage of molecular weights (≤1,000 Da), amino acid content and protein solubility, which reached 89.24, 80.08, and 98.58%, respectively. While, US + MW + EN pretreatment has achieved the highest antioxidant activities by IC50 of 1,1-diphenyl-2-picrylhydrazyl and 2,2-Azinobis (3-ehtylbenzothiazoli- 6-sulfnic acid), which were 3.01 and 1.85 mg/ml, respectively, in addition to the reducing power assay, which was 0.528 at a protein concentration of 5 mg/ml. Therefore, US and combined US-MW techniques can play a promising role in the production of protein hydrolysates and the improvement of their antioxidant properties. Practical applications Nowadays, interest in Chinese sturgeon production has increased as a promising source of protein and antioxidant peptides. The optimal thermal pretreatment can be used to enhance the degree of hydrolysis. The results indicated that the use of ultrasound as a pretreatment enhanced the degree of hydrolysis, which could be useful in the preparation of protein hydrolysate with higher yields. The use of combined US-MW significantly improved the antioxidant properties of the protein hydrolysate. The combined US-MW technique is a novel method for obtaining valuable peptides and protein hydrolysates that can be applied as antioxidant constituents in the food products.

Preparation of highly stable Pickeringemulsions stabilized by food grade particles especially with low concentrations is of concern. In this study, the effects of two-step emulsification procedure with different sequential ultrasonic processes on the storage stability, droplets size, zeta potential, microstructures as well as the rheological behaviors of surimi particles-stabilized Pickeringemulsions with 0.6 oil-water ratio were investigated. The results showed that the surimi particles based-emulsions prepared by the homogenization-ultrasonic (H-U) or ultrasonic-homogenization (U-H) method both possessed excellent physical stability during 14 days storage. Particularly, the stability index of emulsions all exceeded 99.5% in the U-H groups. The confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscope (cryo-SEM) images provide evidence that more particles attached on the oil-water interfaces and the network structures formed via particle-particle interactions obviously arrested phase separation in H-U and U-H emulsions. Moreover, the Pickering emulsions obtained by two-step method all exhibited higher viscosity and storage modulus values, which were also conducive to the special storage stability of samples. In short, the storage stability of protein based-Pickering emulsions can be enhanced using homogenization-ultrasonic (H-U) or ultrasonic-homogenization (U-H) procedure.

Flesh quality changes during postmortem condition are involved with apoptosis initiation. Therefore, flesh quality evaluation based on the alteration of apoptosis process is quite important. Mitochondria, the regulation place of apoptosis, undergo profound changes in fish muscle during postmortem. Thus, this study aimed to investigate whether mitochondrial related parameters during apoptosis process constitutes a putative early fish freshness marker. Mitochondrial profound impairments during postmortem at 4 °C for 5 days demonstrated that the structural changes [double layer membranes and cristae, volume, swelling, membrane potential (ΔΨm), MPTP opening and membrane fluidity] and dysfunctional changes [energy deficiency and disharmony of Ca2+ homeostasis] were occurred during postmortem alteration for energy deficiency and the oxidation by ROS accumulation. Study also investigated energy metabolism related products, TVB-N, lipid and protein oxidation. Compared with the insignificantly increased traditional freshness indicators (except K value) at the initial stage (day 1), the most sensitive parameters based on mitochondrial impairment were [mitochondrial swelling, depolarization of ΔΨm, and membrane fluidity]. Therefore, these above parameters might be considered as suitable and early indicators for freshness evaluation.

This study was carried out to reveal the browning path of ready-to-eat (RTE) crayfish tails during thermal treatment and storage using path analysis. Maillard reactions, lipid oxidation, and phenol oxidation were evaluated in combination with free radical content and FTIR analysis, and direct path coefficients as well as determination coefficients were obtained based on these parameters, such as the absorbance at 294 nm (A294), 5-hydroxymethylfurfural (5-HMF), thiobarbituric acid-reactive substances (TBARS), and total phenols (TP). The result showed that the browning of seasoned RTE crayfish tails was ascribe to the synergistic effect of Maillard reaction and lipid oxidation by the order of determination coefficient. After the crayfish hepatopancreas were removed, the content of A294, 5-HMF, TBARS, and TP declined more than 30%, specifically affecting the direct pathway from lipid oxidation to Maillard reaction and alleviating the browning. However, no significant change of color was observed in the group without thirteen-spices, while TBARS and free radical content increased by at least 16.7%. The removal of hepatopancreas and the control of Maillard reaction were deemed to be a good measure for inhibiting the non-enzymatic browning of RTE crayfish tails.

Acid-induced denaturation and aggregation properties of silver carp actomyosin added with d-gluconic acid-δ-lactone (GDL) during incubation at chilled temperature (4 °C) were studied. Actomyosin underwent aggregation with decreasing pH, as evidenced by increased turbidity and decreased protein solubility in 0.6 M NaCl solution. Ca2+-ATPase activity decreased continually with increasing incubation time in the presence of GDL, accompanied by an initial increase in surface reactive sulphydryl (SH) content, indicating the conformation changes of actomyosin during acidification. Protein solubility in selected solvents and electrophoresis analysis showed that the major myofibrillar proteins, particularly, myosin heavy chain and actin were involved in the formation of protein aggregates mainly through noncovalent bonds including hydrophobic interactions and hydrogen bonds during acidification. The slight decrease in total SH content during acidification suggested that disulphide bonds were also involved in acid-induced aggregation of silver carp actomyosin to a lesser extent.

In this paper, the operating parameters of spray drying after a series of pre-processing were investigated and the properties and qualities of the freshwater mussel meat (FMM) powder were also analyzed. The considerable optimum conditions of spray drying were as follows: the inlet and outlet air temperature of the both deodorization were 180 °C and 80 °C, respectively; the optimum feed concentration for composite deodorization (CD) FMM powder was 30%, and for stewing deodorization (SD) FMM powder 27%; on top of all that, the feed temperature was 50 °C, 45 °C, respectively. In the later analysis, FMM powder was shown to be rich in protein and glycogen, up to 52.7%, 27.71% and 53.4%, 27.69%; meanwhile both the contents of essential amino acids (EAAs) in FMM powders were as high as 44%, which were close to the pattern of FAO/WHO. Thus the FMM powder of the both kinds, namely CD and SD FMM, were thought to be acceptably edible resources with high nutrition for human.

Phospholipid molecular species composition of Chinese traditional low-salt fermented fish (Suan yu) inoculated with different starter cultures was investigated. Fifty-six molecular species of phospholipid including 20 species of phosphatidylcholine (PC), 15 species of phosphatidylethanolamine (PE), 6 species of phosphatidylserine (PS), 9 species of lysophosphatidylcholine (LPC), and 6 species of lysophosphatidylethanolamine (LPE) were identified using ultra-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF-MS). PC (C16:0-C18:1), PE (C16:0-C22:6), PS (C15:0-C22:6), LPC (C22:6) and LPE (C22:5) were the predominant species. Bioactive polyene phospholipids mainly existed in PE. Furthermore, starter cultures exhibited different influence on phospholipid molecular species. Compared to naturally fermented Suan yu, more molecular species of PE and PS as well as polyene phospholipids were detected in the samples inoculated with Saccharomyces cerevisiae 31 and mixed starter cultures.

This study was designed to evaluate and compare the stability, antioxidant and anticancer activities of selenium nanoparticles (SeNPs) decorated with different molecular weight (MW) of chitosan (CS) (1500 Da, 48 kDa, 510 kDa). The size range of well-dispersed SeNPs was effectively controlled by I− first and then coated with CS. The morphology, size and surface charge of generated SeNPs were characterised by several technologies. Fourier transform infrared spectroscopy was used to investigate the relationship between SeNPs and CS. SeNPs decorated with CS (510 kDa) can keep stable for more than 45 days. As observed from the results of a simple photometric system, the antioxidant activities of decorated SeNPs were enhanced compared to undecorated SeNPs. SeNPs coated with higher MW of CS (510 kDa) showed the strongest antioxidant activities. Moreover, the treatments of SeNPs decorated with CS inhibited the growth of HepG2 cells in a time- and dose-dependent manner. The proposed results demonstrated the critical roles of the MW of CS on the stability, antioxidant and anticancer properties of CS-coated SeNPs, which provided an important design cue for future applications of functional foods and additives.

This study was performed to clarify the relationship between internal temperature and quality of steamed shrimps. Shrimps were steamed to different internal endpoint temperature (75°C, 80°C, 85°C, 90°C, 95°C) and evaluated in terms of cooking loss, color, texture and taste active compounds. Results showed that the texture and taste active compounds of steamed shrimps were largely affected by steaming cooking. Cooking loss increased with increasing of internal temperature. Steaming caused lighter muscle and yellow shell of shrimp compared with raw shrimps, and no significant differences in color were observed amongst shrimps with different internal temperature. The hardness and shear force of cooked shrimps increased with increasing temperature in initial stage, followed by a sight reduction when the internal temperature exceeding 85°C. The amount of umami amino acids, sweet amino acids and total free amino acids decreasing with increasing temperature. In addition, it was smaller in the amount of total nucleotides in meat of cooked shrimps than that of raw shrimps, but the amounts of both AMP (5′-adenosine monophosphate) and IMP (inosine monophosphate) in meat of cooked shrimps were almost same, irrespective of internal temperature.

Formulae display:?Mathematical formulae have been encoded as MathML and are displayed in this HTML version using MathJax in order to improve their display. Uncheck the box to turn MathJax off. This feature requires Javascript. Click on a formula to zoom.

Abstract Effects of freezing method and frozen storage duration (16 weeks) at −18 °C on water distribution, microstructure, and taste active compounds of channel catfish fillets were investigated. Results showed that freezing and frozen storage resulted in increase in thawing loss, extracellular space, and loss of some taste active free amino acids and inosine monophosphate (IMP). After 16 weeks of storage, the total content of free amino acids decreased to 77.68% (static air freezing), 78.92% (air‐blast freezing), and 83.13% (liquid nitrogen immersion freezing) of their initial value, while IMP decreased by 45.06% (static air freezing), 25.08% (air‐blast freezing), and 24.11% (liquid nitrogen immersion freezing), respectively. Low‐field 1 H NMR T 2 relaxation data showed an increase in relaxation time of T 21 and T 22 , and a decrease of T 21 population with concomitant increase in T 22 population during frozen storage. Compared with the other two freezing methods, liquid nitrogen immersion frozen fillets with rapid freezing rate showed a less alteration of quality, exhibiting more compact fiber arrangements, less thawing loss and better retention of taste active compounds. Practical applications Frozen storage has been widely used to preserve meat products for a long time, but it inevitably caused undesirable physical, chemical, and structural changes, thus leading to quality loss in texture, flavor, and color. And the degree of quality deterioration of frozen food varies depending on materials, freezing process, and frozen storage conditions. Frozen fillet is one of the main processed fish products. The study of the influence of freezing method and frozen storage on the quality of fillets in terms of water distribution, structural changes, and taste active compounds is of importance to better control the quality of frozen fish products in the industry.

Abstract The freshness of commercial grass carp fillets stored at 4°C was estimated by physicochemical, microbiological and sensorial methods. Total volatile basic nitrogen, trimethylamine, thiobarbituric acid, trichloroacetic acid (TCA)‐soluble peptide, water loss, hypoxanthine, inosine and K value increased significantly ( P &lt; 0.05), while the content of inosine monophosphate was sharply decreased during storage period. Putrescine and histamine were the major amines and their concentrations were significantly ( P &lt; 0.05) higher than other amines at the end of storage period. With regard to the texture profile analysis, the values of texture parameters (including hardness, gumminess, cohesiveness, chewiness and resilience) decreased rapidly within the first 7 days, and then changed slowly until the end of storage, meanwhile, the variation of springiness was not significant during the whole storage period. All the tested microorganisms increased continuously and H 2 S‐producing bacteria (including Shewanella putrefaciens ) was one of major specific spoilage organisms in refrigerated grass carp fillet. Furthermore, sensory analysis of odor and overall acceptability exhibited negative correlations with storage time (−0.96 and −0.94), which was a reflection of the fillets' loss of freshness. Based on the comprehensive results of physicochemical, microbiological and sensory evaluations, grass carp fillets had a shelf life of approximately 10 days during refrigerated storage. Practical applications Grass carp is one of the most important commercial freshwater fish in China and it is popular in market because of its palatability, nutritional characteristic and low price. As we all know, postmortem fish is highly perishable. Investigation of quality changes of refrigerated grass carp is of great significance to fillets' cold‐chain delivery. The quality analysis of refrigerated grass carp fillet will contribute to fishermen and processors in establishing better processing and distribution strategies.

Consumers like dried meat slice, but the desired fiber-like chewiness may be affected by the addition of fish source. Therefore, this study was aimed to investigate the effect of component mixture (pork and fish); particle size (fish mince or cube) and enzyme (transglutaminase and laccase) on dried slice texture. Furthermore, the reason was shown by water distribution, protein secondary structure, and microstructure. Results showed that hardness, chewiness, and tensile strength were the highest at the rate of pork and fish mince by 6:4; at the rate of fish cube and mince by 5:5; and at the addition of transglutaminase (TG) by 0.8%. To explore its reason, it showed the largest water peak area with 3983.8 ± 45.9, 4817.8 ± 209.3 and 3642.5 ± 18.1, the largest decrease of α-helix by 31.1%, 1.8%, 22.6%, and the most compact fiber-like morphology in the above three groups. This study indicated that a slight cross-linking between pork and fish proteins by TG was benefit for fiber-like chewiness, while over-cross-linking was detrimental with more elastic structure formed. In conclusion, percentage of pork to fish, fish cube to mince, and the addition amount of TG all contributed to the final fiber-like chewiness of dried slice significantly.

The antioxidant and antimicrobial effects of equivalent concentrations of both garlic and ginger separately in fresh and powder form on quality attributes of liquid smoked silver carp (Hypophthalmichthys molitrix) during chilled storage were investigated for a period of 24 days.The control and the treated fish samples were analysed periodically for microbiological (total viable count) and physicochemical (pH, colour, water activity, free fatty acid, total volatile basic nitrogen; TVB-N, 2thiobarbituric acid-reactive substances; TBARS) characteristics.The results showed that each spice in either fresh or powder form treatment significantly (P < 0.05) reduced growth of microorganisms as reflected in total viable counts (TVC) from day 6 of storage, lipid oxidation decrease as displayed in TBARS, chemical spoilage decrease as reflected in TVB-N after day 6 of storage as compared to the control samples.The results obtained from this study suggests that garlic and ginger in fresh and powder form, through their combined antioxidant and antimicrobial effects, are potentially useful in preserving liquid smoked silver carp at 4 ± 1°C.

Summary The objective of this work was to study the impact of collagen on softening of grass carp ( C tenopharyngodon idella ) fillets during chilled storage. The fillets were stored under superchilling (−1.5 ± 0.2 °C) and with ice (0.2 ± 0.1 °C) for 21 days, and texture properties, collagen and the related enzyme activities were measured. Results showed that firmness and collagen content were strongly influenced by storage temperature and time. Fillet firmness decreased by 32.3% (superchilling) and 49.6% (ice stored) of the initial values after 3 days of storage, respectively. Total collagen content decreased with time, but different collagen fractions showed variations. Collagen degraded to different extents depending on storage conditions as indicated by SDS ‐ PAGE and amino acid analysis. In addition, collagenase activity declined significantly during the first 3 days, followed by a slow increase. This study demonstrated that collagen degradation was involved in grass carp fillet softening and provided useful information for fillet quality improvement.

Summary To accelerate fermentation and improve quality of fermented fish, the impact of fermentation at elevated temperature on physicochemical, microbiological and flavour characteristics, as well as biogenic amines ( BA s) accumulation of low‐salt fermented fish was investigated. Results showed that increasing temperature at later stage significantly promoted the growth of lactic acid bacteria, retarded the reduction of yeast and increased the titratable acidity, while staphylococci and enterobacteriaceae were inhibited to higher extent when fermented at elevated temperature. BA s contents in samples fermented at 30 °C during later stage were lower than those in the group fermented at 25 °C for 28 days, and the lowest values were observed in the sample initially fermented at 25 °C for 10 days followed by fermentation at 30 °C for 18 days. Furthermore, fermentation at elevated temperature at later stage favoured the formation of desired volatile flavour compounds. Results suggested that fermentation at elevated temperature at later stage could reduce BA s accumulation and enhance quality attributes of low‐salt fermented fish.

In this study, Lactobacillus plantarum 120, Lactobacillus plantarum 145, and Pediococcus pentosaceus 220, which exhibit optimal properties among those isolated from the traditional fermented fish products, were selected as the starter cultures for the preparation of fermented whole carp. During the fermentation, samples inoculated with different single starter cultures showed rapid growth of lactic acid bacteria (LAB), decline in pH, suppression in the growth of main microflora, as well as increase of thiobarbituric acid reactive substances (TBARS) values and total volatile base nitrogen (TVB-N). Quantities of nonprotein nitrogen (NPN) and free amino acids (FAA) were higher in whole carp with starter cultures compared to those in the control. Severe hydrolysis of protein was observed utilizing sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis during fermentation. Moreover, sensory evaluation indicated the higher acceptability of fermented products. The results show that inoculation with the autochthonous starter cultures reduced fermentation time and improved the quality of samples. Therefore, isolates of the strains could be used as potential starters for the fermentation of whole carp.

Suan yu, a type of Chinese traditional fermented freshwater fish in solid form, is cheered among consumers due to its characteristic sensory flavour, primarily taste and smell. The purpose of this study was to investigate the presence of esterase activity of Lactobacillus plantarum 120, Staphylococcus xylosus 135, and Saccharomyces cerevisiae 31, in selecting appropriate processing means to accelerate the formation of the desired flavour in Suan yu. The results showed that all strains exhibited esterase activities in both intracellular and extracellular fractions against p-nitrophenyl (p-NP)-acetate, p-NP-butyrate, and p-NP-octanoate, and also that the maximum activity was observed in the intracellular fraction with p-NP-octanoate. Esterase activities of all strains were inhibited by low pH and low water activity (Aw), with the exception of L. plantarum 120 exhibiting an increase in intracellular activity with decreasing Aw. Moreover, L. plantarum 120 and S. xylosus 135 esterase were negatively affected by decreasing temperature, while a positive influence was observed on the intracellular esterase of S. cerevisiae 31. The results suggested that a low pH, a low Aw and a high temperature would be more appropriate for Suan yu processing to produce more flavour compounds which are acceptable by consumers.

This experiment was conducted to evaluate the efficacy of application of acetic acid and ascorbic acid spray on the surface decontamination and shelf-life of silver carp fish at refrigerated temperature (40C) during 9 days of storage period. Silver carp is one of the most abundant freshwater fish speciesin the world. However, the rapid quality degradation soon after post-mortem makes them highly putrefactive while reducing the nutritional attributes. In this regard, our study aimed at applying organic acids to extend shelf-life of silver carp fish while investigating the quality attributes such as sensory, peroxide values, pH and microbial loads of the fish fillets during 9 days of refrigerated temperature storage (40C). Acetic acid and ascorbic acid are found to have strong antibacterial activities against different microorganisms. Fish fillets samples were treated with alone or in combination with acetic acid and ascorbic acid spray while keeping one group of fish fillets untreated. Total Viable Count (TVC) was found greater in the samples kept untreated and treated alone with acetic acid and ascorbic acid. However, fish fillets treated with acetic acid and ascorbic acid in combination were reported with lesser number of microbial counts. Moreover, Peroxide Value (PV) and pH were significantly lower in the sample treated with in combination of acetic acid and ascorbic acid. Sensory analysis revealed that fish fillets treated with combined treatment had better quality retention at the end of 9 days storage period. The findings suggest that the application of acetic acid and ascorbic acid alone or in different combination have the potential to decrease microbial loads while facilitating the shelf-life of fish fillets during 9 days of refrigerated temperature (40C) storage period.

Synthetic selenium polysaccharides with potential bioactivity have drawn great interest due to the SeO bonds existing in the structure. Herein, N, O-selenized N-(2-carboxyethyl) chitosan (sNCCS) was synthesized through carboxyethylation and selenylation. Various characterizations were performed to identify the structure of sNCCS, indicating that SeO bonds were formed both at the C-6 hydroxyl groups and the introduced C-2 carboxyethyl groups. The highest yield and selenium content of all sNCCS reached 84.5% and 1.553 mg/g, respectively. In vitro evaluation exhibited that sNCCS has excellent bile acid binding capacity, which was 1.63, 2.00, and 2.55-fold higher than that of N-(2-carboxyethyl) chitosan (NCCS). Moreover, it was found that higher selenium content could significantly enhance the antioxidant properties of sNCCS. Importantly, no obvious cytotoxic effect had been observed on Caco-2 cells. Taken together, sNCCS with desirable biological activity and non-cytotoxicity might be considered as an effective ingredient in the fields of food or medicine.