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To improve the antioxidant activity of grass carp hydrolysate, washing and membrane removal pretreatments and ultrasonic treatment were applied in this study. Various pretreatment methods (washing methods and membrane removal methods) for removing the prooxidants and phospholipid in minced fish were evaluated. The effects of ultrasonic treatment prior to enzyme hydrolysis on the antioxidant activities of minced carp hydrolysate were investigated. The minced carp subjected to washing with 0.4% NaCl solution and subsequent membrane removal with CaCl2 and citric acid solution had the lowest content of prooxidants and phospholipid remaining in the minced fish. The hydrolysate produced from washing/membrane removal pretreated carp with ultrasonic treatment for 20 min had the highest ferric reducing antioxidant power and scavenging activities against 1,1-diphenyl-2-picrylhydrazyl and 2,2ʹ-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) radicals. This suggested that the combination approach of washing/membrane removal pretreatment and ultrasonic treatment could improve the antioxidant activity of carp hydrolysate, and this hydrolysate could be a potential antioxidant ingredient for functional foods. [ABSTRACT FROM AUTHOR]

Chitosan coating and plastic wrap coating were investigated for their effects on the quality of grass carp fillets stored at 4 ± 1ºC for a period of 20 days. The fillets were divided into groups of untreated (Control), wrapped with sterile preservative film (PE), and chitosan-treated (1, 2, and 2.5% w/v corresponding to CH1, CH2, and CH2.5, respectively). The final result demonstrated that chitosan coating has positive effects on the microbial inhibition of total volatile count (TVC), lactic acid bacteria (LAB),Enterobacteriaceae, Pseudomonas, H2S-producing bacteria (includingShewanella putrefaciens), andStaphylococcus. With regard to the results of biogenic amines (BAs), putrescine (PUT) and histamine (HIS) were the major amines, and their concentration was significantly (p< 0.05) higher in Control and PE than in chitosan-coated fillets at the end of storage. The final concentration in Control, PE, CH1, CH2, and CH2.5 was 143.7, 160.1, 83.0, 59.4, and 44.2 mg/kg for PUT and 228.0, 57.1, 4.1 3.2, and 2.9 for HIS, respectively. Chitosan coating was found to inhibit the increase of total volatile base nitrogen (TVB-N), microbial population, and total BAs and prolong the shelf life of grass carp fillets. However, sterile plastic wrap coating had little positive effect on maintaining the quality of grass carp fillets during refrigerated storage. [ABSTRACT FROM PUBLISHER]

A two-stage fermentation process of deproteinization and demineralization was used to purify chitin from Antarctic krill shell waste. Two bacterial cultures were isolated and tested for the degradation of krill shell waste. According to the morphological examination, physiological tests, and applied molecular techniques conducted, isolates were identified asBacillus subtilisandLactobacillus plantarum. At a temperature of 37°C, both strains were cultivated separately in flasks containing krill shell waste. At determined periods of time, deproteinization and demineralization of residuals were measured. For deproteinization tests, the liquid phase fermentation of krill shell waste showed protein removal of 88.9% after 60 h. For demineralization tests, the liquid phase fermentation of krill shell waste showed calcium carbonate removal of 84.6% after 72 h. Fourier transform infrared spectroscopy (FTIR) analysis of chitin prepared by the process was carried out and compared with spectra of samples treated by strong acids and bases. [ABSTRACT FROM PUBLISHER]

This study aimed to purify and identify a novel antidiabetic peptides from Chinese giant salamander (Andrias davidianus) protein hydrolysate and to evaluate its anti-diabetic properties against α-amylase and α-glucosidase. The isolation was done by gel filtration, reverse phase chromatography (RF-HLPC), and finally peptide and amino acid sequences were identified by LC/MS/MS system. Our results revealed five novel peptides that strongly inhibited α-amylase and α-glucosidase. The peptides’ amino acid sequences were Cys-Ser-Ser-Val (MW = 393.99 Da), Tyr-Ser-Phe-Arg (MW = 570.99 Da), Ser-Ala-Ala-Pro (MW = 343.89 Da), Pro-Gly-Gly-Pro (MW = 325.99 Da) and Leu-Gly-Gly-Gly-Asn (MW = 415.99 Da) possessing α-amylase inhibitory activity IC50 of 13.76 × 103, 10.82 × 103, 4.46 × 103, 4.23 × 103, and 2.86 × 103 µg/mL, respectively; and for α-glucosidase with IC50 of 206.00, 162.00, 66.90, 63.50, and 42.93 µg/mL, respectively. Intriguingly, the peptide LGGGN showed higher inhibition on both α-amylase and α-glucosidase and could be considered as a potential anti-diabetic inhibitor. [ABSTRACT FROM AUTHOR]

Fermentation has been found as an effective method to decrease the hypersensitive reactions of consumers by freshwater fish, but the reason is not clear. Therefore, the aim of this study was to investigate the impact of pH and acid-activated proteases on the decrease of immunological properties of parvalbumin from freshwater fish, by the indicators of SDS-polyacrylamide gel electrophoresis, western blotting, enzyme-linked immunosorbent assay, surface hydrophobicity and circular dichroism. The results showed that black carp (Mylopharyngodon piceus) had the highest level of immunological properties reflected by quantitation, the content of linear epitopes and conformational epitopes of parvalbumin, and IgE-binding rate. Afterwards, purified parvalbumin from black carp was obtained with purity higher than 95%. Then, for acidification and enzyme models, it indicated that acid-activated proteases were the reason for the decrease of immunological properties. Ulteriorly, the mechanism on the level of protein structure was provided, which showed the decrease of α-helix and the increase of β-turn and random coil, as well as the decrease of surface hydrophobicity had joint contribution for the breaking of conformational epitopes. This study could provide a novel guidance for the decrease of immunological properties of fish and promote fish processing industry further. • Black carp had relatively high allergenicity among 7 freshwater fishes. • Parvalbumin (PV) from black carp was purified effectively. • Allergenicity of PV was decreased by acidic proteases rather than decrease of pH. • The turning of α-helix to β-turn and random coil changed conformational epitope. • The burying of surface hydrophobicity also changed conformational epitope. [ABSTRACT FROM AUTHOR]

The effects of washing and membrane removal pretreatments on the antioxidant properties of grass carp protein hydrolysates prepared through in vitro digestion were investigated. Furthermore, antioxidant hydrolysate was fractionated using ultrafiltration membranes (10, 5, 3 and 1 kDa). Oxygen radical antioxidant capacity ( ORAC), DPPH and ABTS-scavenging activity in a gastrointestinal digest produced from pretreated minced grass carp was increased 1.74-fold, 1.08-fold and 1.72-fold, respectively, compared to untreated minced carp. Compared to the alkaline protease hydrolysate, ORAC, ferric reducing antioxidant power, ABTS- and DPPH-scavenging activity in a gastrointestinal digest prepared from pretreated minced carp were reduced by 11.5%, 60.9%, 16.3% and 78.4%, respectively. The ultrafiltration fraction (<1 kDa) displayed the highest antioxidant activity. The size of molecular weight and the amount of hydrophobic and aromatic residues in hydrolysates played an important role in antioxidant activity. Low-molecular-weight fish hydrolysates could serve as a potential source of functional ingredients for promoting health. [ABSTRACT FROM AUTHOR]

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 < 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 < 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 H2S-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. [ABSTRACT FROM AUTHOR]

The hydrolysis of sarcoplasmic proteins during the growth of Lactobacillus plantarum 120 originally isolated from Suanyu, a traditional Chinese low salt fermented fish, was evaluated. Fermentation was carried out in a fish meat model system at 30C for 96 h. Proteolytic activity of this strain on fish muscle sarcoplasmic protein was determined by proteins, peptides and free amino acids analyses. There was a pronounced hydrolysis of almost all protein bands in electrophoretic pattern by L. plantarum 120. It also resulted in the generation of new peptides and disappearance of original peaks. In addition, the studied strain generated greater amounts of free amino acids than the control, especially for alanine, glutamic acid, phenylalanine, valine, methionine, aspartic acid, isoleucine and leucine. In general, proteolysis of fish sarcoplasmic proteins by L. plantarum 120 occurred during fermentation, resulting in increase in peptides and free amino acids, which may contribute to the taste and aroma of Suanyu. Practical Applications Suanyu is one of the Chinese traditional fermented fish products in South China. According to its characteristic flavor and high nutrition value, Suanyu has been accepted around China in recent year. However, Suanyu is still manufactured on a small scale by spontaneous fermentation. It is difficult to guarantee product quality and increase the efficiency. Lactic acid bacteria is one of the essential agents of the meat fermentation process that contribute to the hygienic and sensory qualities of meat products. Lactobacillus plantarum 120, isolated from Suanyu, exhibited optimal properties as a potential starter in our previous work. Once L. plantarum 120 is used as an industrial starter, it will promote fish muscle proteolysis, shorten the fermentation period and then improve product quality assurance activity. [ABSTRACT FROM AUTHOR]

This study examined the inhibitory effects of catechin, tea polyphenols, gallic acid and Na-citrate on the collagenase activity, collagen degradation and texture change of grass carp (Ctenopharyngodon idella) fillets over a period of 21 days under superchilling (−1.5C ± 0.2C) and ice storage (0.2C ± 0.1C) conditions. The results showed that catechin was the most effective inhibitor of collagenase activity, followed by tea polyphenol and gallic acid. Na-citrate exhibited the lowest inhibitory effect on collagenase activity. All additives were able to suppress the softening of chilled fillets to varying degrees. Catechin effectively retarded the softening of grass carp fillets under both conditions. The firmness of chilled fillets treated with catechin were 72.6 (superchilling storage) and 75.8% (ice storage) higher than of the firmness of control fillets after 3 days of storage, respectively. However, treatments with Na-citrate showed no obvious inhibitory effect on textural deterioration. Practical Applications The texture of fillets when stored in chilled conditions inevitably deteriorated, represented by gapping and decreases in hardness. Recent studies have found that muscle softening is highly associated with collagen degradation induced by collagenase. Thus, the inhibition of collagenase and the stabilization of collagen are of great importance for controlling the autolytic degradation of fish muscle, thus alleviating the texture deterioration of chilled fillets. The inhibitory effect of four selected edible additives on the collagenase activity and texture deterioration of chilled grass carp fillets was investigated. Catechin effectively retarded the softening of chilled grass carp fillets. The present study provides a promising method for maintaining the texture quality of chilled fillet and extending the post-mortem shelf-life. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 1H NMR T2 relaxation that revealed a positive correlation ( P < 0.01) between WHC and the mobility of the immobilised water (T21 relaxation time). Meanwhile, negative correlation could be established between intact desmin and drip loss ( P < 0.01). Intact desmin was extremely correlated with shear force ( P < 0.01) and positively correlated with calpains activity ( P < 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. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (A 294), 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 A 294 , 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. [ABSTRACT FROM AUTHOR]