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Summary: Textural deterioration is a severe problem in fish industry. In order to study the role of structural proteins in refrigerated grass carp, myofibrillar proteins and collagen degradation were investigated at different stages. Results revealed that connective tissues of fish muscle disintegrated from day 1, failing to hold muscle myotomes together, with a decrease of shear force. Meanwhile, collagen solubility increased from day 1 and degradation of nebulin was observed after 3 days, while there was no obvious change in the bands of myosin heavy chain and actin. Furthermore, Pearson coefficient analysis revealed that insoluble collagen (ISC) and nebulin were significantly correlated with shear force. Negative correlation was established between drip loss and contributing factors (ISC, titin and nebulin). All results suggested that textural loss of post‐mortem grass carp fillets was mainly mediated by the degradation of collagen and to a lesser extent by myofibrillar proteins at the early storage. [ABSTRACT FROM AUTHOR]

BACKGROUND: Apoptosis activation is an essential research to reveal the triggering mechanism of flesh quality deterioration. This study was aimed at explaining apoptotic mechanism of postmortem fish in terms of caspases activation, cytochrome c (cyt‐c) release, B‐cell lymphoma 2 (Bcl‐2) and Bcl2‐associated X (Bax) protein levels, transcriptional levels of its molecules, and apoptosis‐inducing factor (AIF) translocation at 4 °C for 5 days. RESULTS: Activation of caspase‐9, caspase‐8, caspase‐3 and the release of mitochondrial cyt‐c were observed during storage. The decreased Bcl‐2 protein levels, increased Bax protein expressions and Bax/Bcl‐2 ratio were major steps for inducing apoptosis. Collectively, transcriptional regulation of Fas ligand (FasL), apoptotic protease activating factor‐1 (Apaf‐1), inhibitors of apoptosis proteins (IAPs), myeloid cell leukemia‐1 (Mcl‐1), c‐Jun N‐terminal kinase (JNK) and p38 mitogen‐activated protein kinase (MAPK) indicated that extrinsic apoptotic pathways (FasL/caspase‐8/caspase‐3) and intrinsic pathway [(JNK and p38 MAPK)/(Bcl‐2, Bax and Mcl‐1)/cyt‐c/Apaf‐1/caspase‐9/caspase‐3] were involved in apoptotic process. Mitochondrial AIF translocation to nuclear indicated that AIF mediated caspase‐independent pathway. CONCLUSION: Therefore, transcriptional and translational alterations of multiple signaling molecules acted important roles in regulating apoptosis activation in postmortem process. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Alterations of apoptosis have notable influences on flesh quality, but the mechanism is still unclear. Thus, apoptotic behaviors and related triggering mechanisms need to be explored. Fish muscle was prepared and stored at 4 °C for 0, 24, 48, 72, 96, and 120 h for apoptosis analysis. Results showed that positive apoptotic nuclei were positively correlated with drop loss and negatively correlated with shear force and water holding capacity (p < 0.05). Results showed that the triggering apoptotic mechanisms were involved with enhanced transcriptional levels of caspase-2, 3, 7, 8, and 9 through mitochondria and death receptor pathways in the muscle of grass carp. The decreased ATP content, changed cytochrome c redox state, increased protein levels of HSP27 and HSP 90, and enhanced activity of cathepsin (B, L, and D), calpain, and serine proteinase were involved in apoptosis activations. Results indicated that caspases, energy metabolism, cytochrome c redox state, heat shock protein expressions, and protease activities played critical roles in apoptosis alterations in carp muscle during refrigerated storage. [ABSTRACT FROM AUTHOR]

Summary: The disruption of structural integrity could affect flesh quality changes. This study investigated the disruption of muscle integrity and the affecting factors in postmortem fish at 4 °C for 5 days storage. Haematoxylin–eosin staining indicated that profound disruption of structural integrity was observed for the changes of dissolved nucleus, irregular shape of myofibrils and loose attachment. The increased activities of β‐N‐acetyl‐glucosaminidase (NAG) and α‐Glucosidase (AG) enzymes confirmed the profound disruption of integrity in postmortem muscle. The abnormal up‐regulated gene expressions of claudin‐11, claudin‐12, claudin‐15a, claudin‐15b and myosin light chain kinase (MLCK) implied the disrupted intercellular integrity. The impaired cellular integrity and the increased oxidative damage was due to the decreased antioxidant capacity, which was regulated by the decreased transcriptional levels of antioxidant enzymes. Collectively, this study provided a partial molecular mechanisms for the disruption of structural integrity and the changes of flesh quality in postmortem fish muscle. [ABSTRACT FROM AUTHOR]

BACKGROUND: Textural deterioration is a serious problem in chilled fish flesh. Cysteine proteinases are proposed to participate in disintegration of collagen fibers during this process, while its mechanism remains elusive. In the present study, a cysteine proteinase was purified from grass carp muscle and identified by mass spectrometry, and its effect on structural changes of collagen fibers was investigated. RESULTS: During storage at 4 °C, cysteine proteinase activity in fillets increased to 1.53‐fold at day 5 and maintained a high level later, and this variable was related to a decline in shear force and an increase in drip loss. A 29 kDa cysteine proteinase was purified through ammonium sulfate precipitation and column chromatography, and identified as cathepsin L. Cathepsin L caused collagen fibers to partly disintegrate into fibril bundles and individual fibrils at 48 h, while the triple helical structure of collagen molecules remained stable. Release of soluble proteins and glycosaminoglycans from cathepsin L‐treated collagen fibers was time dependent, coinciding with a release of 4.12 ± 0.13% and 8.57 ± 0.03% at 48 h respectively. However, 0.85 ± 0.02% of hydroxyproline was freed from cathepsin L‐treated collagen fibers at 48 h. Furthermore, scanning electron microscopy revealed that the inhibitory effect of cathepsin L could retard the destruction of intramuscular connective tissues (IMCTs). CONCLUSION: These results indicated that cathepsin L might be involved in collagen fiber breakdown by degrading collagen‐associated proteoglycans during textural deterioration of grass carp. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Summary: One of the most worrisome problems with frozen fish is its undesirable softening texture, due in part to the alteration of fish protein structure. Therefore, a new immersion freezing (IF) technology with the edible medium, which was proven to improve food freezing speed and quality, was compared with air blast freezing (AF) and liquid nitrogen freezing (LNF) on the scope of protein structure. Protein fractions, structure, chemical bonds and particle size of the grass carp muscle were used as indicators. At the end of 24 weeks of frozen storage, the content of salt‐soluble protein in IF (106.22 ± 1.01 mg g−1 meat) was significantly higher than that of AF (90.77 ± 1.11 mg g−1 meat) and LNF (97.44 ± 1.40 mg g−1 meat) (P < 0.05). Compared to AF, the α‐helix content of IF and LNF was higher, the content of β‐turn and random coil was lower, while no statistical difference was detected in IF and LNF groups (P < 0.05). Meanwhile, the intrinsic fluorescence intensity, ionic bonding and hydrogen bonding in IF were significantly higher than in AF. The lowest value of D[3,2] was observed in the IF group after 24 weeks storage. Therefore, IF is an effective approach to reducing protein denaturation and can be adopted as an alternative freezing method. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the in vitro susceptibility of grass carp (Ctenopharyngodon idella) oxidized myosin, with the treatment of H 2 O 2 levels being 0, 25, 50, and 100 μmol/L, respectively. The results showed that in vitro oxidation of myosin, reactive oxidative species promoted protein modifications that propagated the conformation changes on myosin secondary structure, leading to a significant increase (P < 0.05) in the protein carbonyl content in the high oxidation treatment, when compared to the low and medium treatments. The results of the Western blot analysis and sodium-polyacrylamide amide-dodecyl sulfate gel electrophoresis demonstrated that in vitro oxidation actively promoted the degradation of protein molecular weight and Desmin (53 kDa) deterioration in the sample with the highest concentration treatment of H 2 O 2. Circular dichroism spectra showed a decrease in α-helix content from 70.1% to 29.8% and an increase in β-sheet percentage from 5.6% to 17.4%. Meanwhile, cysteine and methionine as the free amino acids were most susceptible to oxidative change due to their high sensitivity to the reaction of the sulfur group of amino acids. Protein degradation induced by oxidation resulted in significant changes to the protein secondary structure, as evidenced by the observation of oxidized myosin under different H 2 O 2 levels. [ABSTRACT FROM AUTHOR]

BACKGROUND Texture softening is always a problem during chilling of grass carp fillets. To solve this problem and provide for better quality of flesh, understanding the mechanism of softening is necessary. Gelatinolytic proteinases are suspected to play an essential role in the disintegration of collagen in softening of fish flesh. In the present study, the types and contribution of gelatinolytic proteinases in chilled fillets were investigated. RESULTS: Four active bands (G1, 250 kDa; G2, 68 kDa; G3, 66 kDa; G4, 29 kDa) of gelatinolytic proteinases were identified in grass carp fillets by gelatin zymography. The effect of inhibitors and metal ions revealed that G1 was possibly a serine proteinase, G2 and G3 were calcium‐dependent metalloproteinases and G4 was a cysteine proteinase. The effect of the inhibitors phenylmethanesulfonyl fluoride (PMSF), l‐3‐carboxy‐trans‐2,3‐epoxy‐propionyl‐l‐leucine‐4‐guanidinobutylamide (E‐64) and 1,10‐phenanthroline (Phen) on chilled fillets revealed that gelatinolytic proteinase activities were significantly suppressed. Collagen solubility indicated that metalloproteinase and serine proteinase played critical roles in collagen breakdown during the first 3 days, and cysteine proteinase revealed its effect after 3 days. Meanwhile, during chilled storage for 11 days, the final values of shear force increased 19.68% and 24.33% in PMSF and E‐64 treatments when compared to control fillets respectively, whereas the increase after Phen treatment was 49.89%. CONCLUSION: Our study concluded that the disintegration of collagen in post‐mortem softening of grass carp fillets was mainly mediated by metalloproteinase and to a lesser extent by serine proteinase and cysteine proteinase. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

This research evaluates the quality and acceptability of 25%, 50%, and 75% fish protein concentrate (FPC) egg substituted cakes. Proximate chemical composition, batter and cake physical quality, microbial activity, and sensory evaluation were carried out. An impressive increase in protein, fats and ash content was noticed in GPSC. By increasing the FPC concentration, the viscosity of batters and cake volume decreased, while the specific gravity increased. In texture, the hardness, chewiness, and gumminess were increased while elasticity and cohesiveness were decreased with increase in substitution. An increase in substitution increased baking loss (BL) but reduced the water activity (aw) and the number and size of air bubbles in cake batter. By evaluating microbial activity, the total plate count (TPC) value increased, and the total fungal count (TFC) decreased while the cake crumb showed inconsistent change. The cake with 75% egg substitution was highly nutritious but displayed lower sensory attributes due to slight fishy flavor and dark color, while 25% and 50% GPSCs showed almost similar sensory attributes but nutritional value of 50% GPSC was higher than 25% GPSC. So, the cake with 50% substitution is a better option to prepare a good quality protein-enriched cake with acceptable sensory attributes. [ABSTRACT FROM AUTHOR]

Summary: This study aimed to determine the role of intramuscular connective tissue (IMCT) in softening of ice‐stored grass carp (Ctenopharyngodon idella) fillet. The change in important proteins in IMCT and impact of IMCT destruction in fish softening were both investigated. The exogenous collagenase was used to differentiate the role of IMCT. Results showed that decorin, elastin and collagen in IMCT decreased by 71%, 48% and 54%, respectively. Decorin and elastin were mainly degraded in the primary stage, while collagen decreased mainly in the later stage. Then, IMCT destruction experiment showed that collagenase was quite effective for destruction of IMCT, while myofibre tissue was not affected. Subsequently, specific role of IMCT could be distinguished. Decrease in shear force became twofold faster in the collagenase group at the beginning than that in the control group, indicating a quite important role of IMCT in maintaining fish texture, especially in the primary stage of storage. [ABSTRACT FROM AUTHOR]

Summary: The aim of the present study was to investigate the underlying mechanisms of softening texture in chilled grass carp filletsunderpinning collagen solubility, gelatinolytic proteinase activity and physicochemical parameters. Acid‐soluble collagen (ASC) and heat soluble collagen (HSC) increased markedly, while a significant decline was detected in total collagen and insoluble collagen (ISC) during the first 3 days of storage, coinciding with a loss of shear force and water‐holding capacity (WHC) (P < 0.05). Moreover, the activity of gelatinolytic proteinases was gradually activated and reached the peak at day 3 (P < 0.05). Pearson coefficient analysis showed that gelatinolytic proteinase activity revealed a significant correlation with collagen solubility. Total collagen, ASC, ISC and HSC were significantly correlated with shear force and WHC. Our study clarified that the increase of collagen solubility by gelatinolytic proteinases played an important role for texture softening in the early stage of chilled grass carp fillets. [ABSTRACT FROM AUTHOR]

In order to clarify the action of a seasoning mixture of salt and Chinese liquor in maintaining the hygienic and quality characteristics of refrigerated grass carp, the changes in physicochemical properties, biogenic amines, and microbial growth in grass carp fillets during storage at 4°C for 30 days were investigated. Results showed that fillets lightly salted with Chinese liquor had lower values of total volatile basic nitrogen, drip loss, biogenic amines contents, and higher hardness as well as stable pH during storage, compared to the untreated or individual salted groups. The increase in total viable counts and total psychrophile counts were significantly inhibited by combined adding salt and Chinese liquor. Additionally, Illumina sequencing analysis showed Enterobacteriaceae and Carnobacteriaceae were the major spoilage bacteria species in untreated samples at the end of storage, but they were highly inhibited by adding salt and Chinese liquor. Practical applications: Refrigerated storage can better maintain the fresh quality of fish because it is stored under nonfrozen conditions, but the shelf life is limited due to the action of microorganisms and endogenous enzymes. Food seasoning ingredients have the characteristics of high safety, low cost, and convenient application. The combination of salt with other ingredients in fish curing to develop low‐salt preservation techniques has attached increasing interest. The present study showed that curing of grass carp using salt combined with Chinese liquor can largely delay chemical changes, lower the accumulation of putrescine and cadaverine, and inhibit the growth of spoilage microorganisms in refrigerated fish fillets compared to the untreated group. This study provided a promising cost‐efficient and simple preservation technique of fish. [ABSTRACT FROM AUTHOR]

The effects of freezing method on ice crystal, distribution of water and freshness properties of grass carp during frozen storage was investigated. The freezing methods contained air‐blast freezing (AF), immersion freezing (IF) and liquid nitrogen freezing (LNF). Results showed that the freezing speed of IF samples was 4.22 times that of AF samples. Ice crystals of IF samples were smaller than that of AF samples (p <.05). Consequently, there was less damage to muscle fiber, lower water mobility and high retention of texture in IF samples during frozen storage. Meanwhile, equivalent diameter and area ratio of ice crystals increased by 101.2% and 38.8% (IF), 396.8% and 211.3% (LNF) after 5 months of frozen storage. Compared with LNF samples, IF samples had the lower growth rate of ice crystals, almost the same thawing loss and muscle tissue state. Principal component analysis showed that IF was similar to LNF in maintaining quality characteristics of fish. Overall, IF was a promising way to delay the degradation of fish during frozen storage. Practical Applications: Liquid nitrogen freezing technology is one of the mature technologies on the market with many advantages because of its fast freezing speed; however, it is prone to cause low‐temperature fracture and whitening of products, affecting sensory quality of products. Immersion freezing technology and the coolants have been improved in recent years. The coolants used in immersion freezing can be recycled for many times and reduce costs of freezing. Once the effect of immersion freezing technology on quality of food is similar to that of liquid nitrogen freezing and the cost is relatively low, it is expected that the immersion freezing technology will be further promoted by industry processors. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the changes in the amino acid and fatty acid profiles of wheat flour noodles when supplemented with grass carp protein concentrate (GCPC) at levels of 0%, 10%, 20% and 30% (referred to as CN, GCPC10, GCPC20 and GCPC30). The protein quality of the products was also determined using the digestible indispensable amino acid score (DIAAS). The indispensable amino acids (IAA) content increased (347.93 to 417.03 mg/g protein) with the increasing levels of GCPC from 0 to 30%. The total IAA content of all the noodle formulations were above the recommended daily allowances for adults (277 mg/g). The content of dispensable amino acids in CN on the other hand was significantly the highest (636.67 mg/g protein) when compared to GCPC10 (611.82 mg/g), GCPC20 (587.19 mg/g) and GCPC30 (580.48 mg/g). The calculated DIAAS values with respect to young child and adult age patterns were 36% and 43% (lysine) for CN, which in both cases the protein quality is graded poor (< 75%). GCPC supplemented noodles were found to have DIAAS values from 72 to 99%, which in most cases were under the "good" (75–100%). The ratios of omega-6 (n-6) to omega-3 (n-3) fatty acids ratio was recorded 3.94, 3.62 and 3.53 for GCPC10, GCPC20 and GCPC30 respectively, all values being lower than the maximum recommended, 4.0. The polyunsaturated fatty acids (PUFA) to saturated fatty acids (SFA) ratio was recorded 2.05, 1.47, 1.36, and 1.34 for CN, GCPC10, GCPC20 and GCPC30 respectively, the minimum recommended ratio being 0.45. The study has thus concluded that incorporating GCPC into wheat flour noodles can upgrade the protein quality and balanced fatty acid content to promote healthy wheat flour noodle meals. [ABSTRACT FROM AUTHOR]

Effects of three carp species on texture, color, and aroma properties of Chinese traditional fermented freshwater fish (Suan yu) were investigated. Suan yu were produced from Ctenopharyngodon idella (Grass Carp, GC), Hypophthalmichthys molitrix (Silver Carp, SC), and Cyprinus carpio (Common Carp, CC) as the control. GC displayed the highest hardness and resilience, while SC showed the lowest texture except for springiness (p <.05). GC had the greatest L* and ΔE* values but the least a* value (p <.05). Esters (7), alcohols (7), acids (9), aldehydes (8), ketones (1), hydrocarbons (4), and others (5) were identified by GC‐MS in all samples. E‐nose analysis showed a remarkable difference in the overall aroma profile among all samples. Sensory evaluation and PCA analysis indicated that grass carp could be used as an alternative raw material for Suan yu production, which would improve the utilization of freshwater fish. Practical applications: Suan yu is a type of Chinese traditional fermented freshwater fish with a unique flavor, which is popular among consumers. Such products are commonly manufactured from fresh common carp (Cyprinus carpio) with long‐term anaerobic fermentation. Grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) are popular among consumers as major domesticated fish in China with higher annual harvests than that of common carp, which show potential as raw materials for Suan yu production. It is the first time to investigate the texture, color, and aroma of Suan yu produced from the three carp species (grass carp, silver carp, and common carp) in the same process and to evaluate their quality differences and acceptability. This will help increase the sources of raw materials for Suan yu production and improve the utilization of freshwater fish. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate the quality of wheat flour noodles supplemented with 0%, 10%, 20% and 30% grass carp protein concentrate (GCPC). Proximate composition, color analyses, cooking properties (cooking time, cooking loss, swelling index and water absorption index), texture profile analyses (TPA), and sensory evaluations were performed. Significant (p ≤ 0.05) increases in the crude protein (18.94–35.19%), crude fat (0.88–1.06%), and ash (0.89–1.02%) were recorded for GCPC supplemented cooked noodles. Brightness (L*), redness (a*) and yellowness (b*) of GCPC 10–30% fortified cooked noodles was recorded as 77.00–69.97, 1.50–2.81 and 19.08–22.25, respectively. Cooking loss (CL) and optimal cooking time were significantly (p ≤ 0.05) increased with increased level of GCPC from 0%-30%, with readings of 6.13% −8.90% and 7.53–11.77 min, respectively. Swelling and water absorption indices showed a decreasing trend at 2.33–1.77 and 102.6–78.49%, respectively. A significant (p ≤ 0.05) decreasing trend in hardness (24.50–19.03N) was observed for cooked noodles with increased level of GCPC, while the remaining TPA parameters were significantly different at p>.05. Sensory analyses showed higher preference for control noodles and noodles fortified with 10% GCPC. [ABSTRACT FROM AUTHOR]

This study assessed effects of high pressure processing on physicochemical quality and endogenous enzyme activities of grass carp fillets stored at 4 ºC for 21-day storage. Fresh fillets were vacuum-packed and subjected to high pressure processing (0.1, 200, 300, 400, 500, and 600 MPa at room temperature for 15 min). Results showed that high pressure processing significantly delayed microbial growth, and reduced total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substances (TBARS) levels of grass carp fillets, especially for the 600 MPa group. On the 21st day, the corresponding increases of 6%, 35%, 45%, 43%, and 53% in hardness were observed for 200 MPa, 300 MPa, 400 MPa, 500 MPa, and 600 MPa samples compared with control samples, respectively. In addition, enzyme activities in different groups decreased during storage. Among them, calpain, and myofibril-bound serine proteinases (MBSP) activities were immediately reduced after high pressure treatments, while the activities of collagenase, cathepsin B, and cathepsin D were significantly (P < 0.05) inhibited when the pressure exceeded 400 MPa. However, the pressure treatments activated cathepsin L initially, and then the activity gradually decreased in treated samples. Generally, high pressure processing reduced activities of most of the endogenous enzymes and improved the quality and extended the shelf life by at least 4 ~ 6 days of refrigerated grass carp fillets. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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 NaN3 solution to reduce microbial activity or in iodoacetic acid solution to exclude cathepsin activity before ice storage. Treatment with NaN3 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 NaN3 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 NaN3 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 [ABSTRACT FROM AUTHOR]

The inhibitory effect of allicin on proteolytic enzymes and textural deterioration of ice-stored grass carp ( Ctenopharyngodon idella) fillets was investigated. The results of in vitro study showed that allicin inhibited the activity of cathepsin B, L and D, calpain and collagenase in crude extract of grass carp muscle. Among endogenous enzymes, cathepsin B, L and collagenase were the most susceptible to allicin. Proteolysis of myofibrillar proteins by either crude enzyme or cathepsin B and L was almost prevented by allicin when employed at a concentration higher than 100 m m. After storage of 21 days, shear force of fillets treated with allicin at 10-100 m m was 39-51% higher than that of control. Myofibrillar proteins of fillets during storage were well protected against degradation when allicin concentration increased to 100 m m, as evidenced by SDS- PAGE. Therefore, allicin could be a potential broad-spectrum inhibitor to retard softening of fish fillets via mitigating myofibrillar proteolysis by endogenous enzymes especially cathepsin B and L during ice-storage. [ABSTRACT FROM AUTHOR]

In this study, grass carp peptides were prepared by enzymatic hydrolysis of grass carp protein using the combination of Alcalase and Neutrase, and angiotensin-I converting enzyme ( ACE) inhibitory activity in vitro, antihypertensive activity in vivo, antioxidant activities, and physicochemical properties of peptides achieved from grass carp protein were characterised after ultrafiltration and desalted processes using mixed ion exchange resins. The purified peptides exhibited strong ACE inhibitory activity ( IC50 = 105 μg mL−1), antihypertensive activity with the maximal drop for systolic blood pressure ( SBP) of 43 mmHg at a dosage of 100 mg per kg body weight in spontaneously hypertensive rat ( SHR), and antioxidant activities indicated by thiobarbituric acid-reactive substance values in a liposome-oxidising system, radical-scavenging activity and chelation of metal ions (Fe2+). The molecular weight of peptides was <1000 Da. Compared to grass carp protein, the peptides separated from enzymatic hydrolysates possessed similar amino acid compositions, but contained higher concentrations of essential amino acids. Moreover, the peptides exhibited excellent solubility at a wide range of pH values from 2 to 10, and lower apparent viscosity than the protein. The peptides separated from enzymatic hydrolysates might be used as a promising ingredient in antihypertensive functional foods and nutraceuticals. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the impact of collagen on softening of grass carp ( Ctenopharyngodon 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. [ABSTRACT FROM AUTHOR]

Cysteine cathepsin-associated degradation of muscle proteins have been assumed to be crucial to the softening of chilled fillet. The effect of aqueous extract of Alliums on cathepsin-induced proteolysis and texture deterioration of ice-stored carp fillets was evaluated. Among all treatments, extracts of scallion and garlic were the most effective inhibitor of cathepsin B, reducing the enzyme activity by more than 40 % after storage of 3 days, whereas extracts of scallion and leek had the greatest inhibitory effects on the cathepsin L activity, resulting in corresponding reduction in enzyme activity of 65 and 57 %, respectively. Extracts of scallion and garlic were the most effective treatments in impeding accumulation of TCA-soluble peptides and breakdown of myofibrillar proteins as validated by SDS-PAGE pattern. After storage of 21 days, the shear force of fillets treated with scallion and garlic extracts were approximately 30 % higher than those of control, whereas the treatments with other Allium extracts showed no inhibitory effect on textural deterioration. The results demonstrated that the treatment of grass carp fillets with extract of scallion and garlic has the potential to mitigate the endogenous cathepsin-induced softening of ice-stored grass carp fillets. [ABSTRACT FROM AUTHOR]

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 (ΔΨ m), 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 ΔΨ m , and membrane fluidity]. Therefore, these above parameters might be considered as suitable and early indicators for freshness evaluation. [Display omitted] [ABSTRACT FROM AUTHOR]

Changes of textural properties and cathepsin activity of grass carp fillets during storage in superchilling (--1.5 ± 0.2 °C) and ice (0.2 ± 0.1 °C) was investigated, and the function of cathepsin in quality deterioration of grass carp fillets was discussed. Results showed that shear force of superchilled and ice-stored fillets decreased by 50% and 55% after 6 days of storage, respectively. The cathepsin activies in different fractions changed significantly during storage at both conditions. Cathepsin B, B+L activities in sarcoplasma, myofibrillar and heavy mitochondrial fraction significantly increased during the early 3 days postmortem, accompanied by remarkable reduction of corresponding activity in lysosome. Cathepsin D activity in sarcoplasma and myofibrillar significantly increased during 6 days of storage with corresponding decrease in lysosome and heavy mitochondria. Correlation analysis showed that changes of shear force of grass carp fillets were significantly correlated with integration of cathepsin B, D and B+L throughout storage time (r² > 0.94). As derived from the first-order exponential decay model, the enzyme efficiencies (ka) of cathepsin B and B+L were more than twofold higher than those of cathepsin D, suggesting the major role of cathepsin B and B+L in textural deterioration of grass carp fillets in chilling storage. [ABSTRACT FROM AUTHOR]

The effects of different microbial inoculation strategies on the quality of Chinese traditional rice mash grass carp were investigated. Individual inoculation (Pediococcus pentosaceus 220, Staphylococcus xylosus 135, Saccharomyces cerevisiae 22), and mixed triple inoculation of the above strains (Pediococcus-Staphylococcus-Saccharomyces , PSS) were employed, including an uninoculated control. It was found that the inoculated microbes proliferated differently, depending on the inoculation regime. The decreases of pH, hardness, and increases of TCA-soluble peptides were accelerated, while the accumulation of TVB-N and TBARS was reduced in all inoculated groups. A significantly higher level of total free amino acids was found in PSS-inoculated grass carp (P < 0.05), as well as alcohols and esters. Moreover, the total sensory score of PSS-inoculated grass carp with 15-day fermentation was closest to the control with 30-day fermentation. Consequently, the inoculation of a mixed starter culture could help reduce the fermentation time of rice mash fish by 50% while providing the optimum texture and flavor. • Selected bacteria and yeast improved the quality of rice mash grass carp. • Co-inoculation obviously retarded the accumulation of TVB-N and TBARS. • Co-inoculation accelerated pH decrease and formation of texture. • Co-inoculation produced more total free amino acids, alcohols and esters. • Co-inoculation shortened fermentation time by 50%. [ABSTRACT FROM AUTHOR]

A diffusion model has been developed for predicting the change of moisture content in lightly salted grass carp fillets under the consideration of shrinkage and variable volumetric effective diffusivity. The established relationship between moisture content, temperature, and effective diffusivity validated the effectiveness of considering the variable volumetric effective diffusivity. The appearance of shrinkage during drying and the shrinkage coefficient have been determined for better predicting the variation of moisture content during drying to provide a thorough theoretical basis for industrial processes. [ABSTRACT FROM PUBLISHER]

Herein, the effects of chitosan (CH) coating with different water-soluble polyphenol extracts (pomegranate peel (PPE), grape seed (GSE) and green tea (GTE)) through vacuum impregnation on the quality retention and microflora of refrigerated grass carp fillets were studied. Generally, the quality degradation of carp fillets was remarkably alleviated using coatings when compared to the control. As suggested by microbial enumeration and high-throughput sequencing, protective coatings were conductive to inhibit bacteria growth, especially spoilage bacteria of Pseudomonas. As a result, the indicator related to bacteria such as total volatile basic nitrogen (TVB-N) and K value had lower levels in coating groups than that in control. In addition, coating also slowed down the deterioration of physical properties of color, texture and water holding capacity in fillets, giving fillets a better edible quality. By contrast, the fillets treated by composite coatings had better quality during storage when compared to chitosan coating alone, and a relatively good synergistic antibacterial effect between chitosan and extracts was also observed, especially for CH-GTE. Overall, the best performance to inhibit quality deterioration was recorded in CH-GTE, with the lowest values of TVB-N, TBARS, K-value and water loss, and highest values of shear force and sensory preference among groups. • Vacuum-assisted chitosan coatings with different polyphenol extracts on fillets quality were studied. • Chitosan coatings with polyphenol extracts showed synergistic preservative effect. • Mixing green tea extracts showed the best result to hold the physical states of fillets. • Protective coatings effectively inhibited the growth of spoilage bacteria of Pseudomonas. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • DIA-based proteomics revealed new texture biomarkers for grass carp fillets (GCF). • Isobutyryl-CoA dehydrogenase, mitochondrial was a key marker for chilled GCF. • [Phosphatase 2A protein]-leucine-carboxy methyltransferase marked chilled GCF. • Staphylococcal nuclease domain-containing protein 1 was a key marker for iced GCF. Consumers care about the texture of fresh fish flesh, but a rapid quantitative analytical method for this has not been properly established. In this study, texture-associated biomarkers were selected by DIA-based proteomics for possible future application. Results indicated a significant decline in texture and moisture characteristics with extended storage under chilled and iced conditions, and flesh quality was categorized into three intervals. A total of 8 texture-associated biomarkers were identified in the chilled storage group, and 3 distinct ones in the iced storage group. Biomarkers were further refined based on their expression levels. Isobutyryl-CoA dehydrogenase, mitochondrial and [Phosphatase 2A protein]-leucine-carboxy methyltransferase were identified as effective texture-associated biomarkers for chilled fish, and Staphylococcal nuclease domain-containing protein 1 for iced fish. This study provided suitable proteins as indicators of fresh fish flesh texture, which could help establish a rapid and convenient texture testing method in future studies. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to investigate the effect of superchilling at −3°C compared with ice storage at 0°C on the biochemical and physical properties of grass carp fillets. Fillets stored at −3°C showed significant changes in whiteness, drip loss and textural hardness, while changes in pH, total volatile basic nitrogen and TCA-soluble peptides were slowed down. Partial denaturation of myosin as demonstrated by differential scanning calorimetry differed between fillets stored at −3 and 0°C in that the transition peak showed a left shoulder at −3°C and sharpened at 0°C. Detachments between muscle cells and formation of cracks within cells were accelerated during storage at −3°C, and from 10days on, clear spaces between and within cells were observed with the concurrent appearance of white spots on the surface of fillets, suggesting the formation of both extra- and intracellular large ice crystals. [Copyright &y& Elsevier]

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 R 2 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. • Fish freshness was classified into three levels by hierarchical cluster analysis. • Parvalbumin (PV) in sarcoplasm and drip could indicate grass carp freshness. • PV from grass carp was purified effectively. • Colloidal gold immunochromatographic assay for fish freshness was established and effective. • The detection in drip sample was better than sarcoplasmic protein sample. [ABSTRACT FROM AUTHOR]

• IF reduced thawing loss and maintained the water holding capacity during storage. • IF sample had small and uniform distribution of ice crystals during storage. • IF sample had a shorter T 2 relaxation time during storage. • IF effectively maintained the content of unfrozen water during storage. • IF was an effective method to reduce water migration of grass carp during storage. Recently, immersion freezing (IF) has attracted the attention of many food researchers due to its potential in improving the quality of frozen food. In this study, the effects of air blast freezing (AF), IF and liquid nitrogen freezing (LNF) on the water holding capacity ice crystals, and water migration in grass carp muscles during frozen storage were evaluated. The thawing loss in AF, IF and LNF samples were 13.88 %, 5.49 % and 7.08 %, respectively, and was significantly lower in IF samples than in AF and LNF samples (P < 0.05). Besides, the water holding capacity and pH of all samples gradually decreased during frozen storage. Smaller and more regular intracellular ice crystals were observed in frozen samples during LNF and IF compared with AF. Moreover, IF and LNF had positive effects on the size and distribution of ice crystals. Low field nuclear magnetic resonance (LN-NMR) results showed that IF reduced water migration during frozen storage. In addition, with prolongation of frozen storage time, IF effectively maintained the content of unfrozen water. Therefore, IF can be used as an alternative to the rapid freezing of grass carp with better restriction of water in tissues. [ABSTRACT FROM AUTHOR]

Chitosan (CS) cross-linked films were prepared using the Maillard reaction (CMR). Layer-by-layer casting created additional layers using alginate dialdehyde (ADA) containing cinnamaldehyde nanoemulsions (CANE) and CS. The ability to preserve grass carp fillets was evaluated along with the effects of CANE concentration on the microstructure, physicochemical properties, controlled-release behavior, antioxidation, and antibacterial activities of the films. In all films, Schiff base-induced bonds, electrostatic interactions, and hydrogen bonds brought the layers closer together, improving the mechanical properties (e.g., a 70% increase in tensile strength and a 34% increase in breaking elongation) and barrier capacity (e.g., inhibiting ultraviolet, water vapor, and oxygen transmission). CANE can improve the antioxidant activity, antibacterial activity, and sustained release characteristics of films. More importantly, over the 8-day storage period, the fish packaged using the active films were better than those in the control, commercial PE, and CS films in terms of thiobarbituric acid reactive substances, pH, texture, total viable counts, and volatile basic nitrogen with indicator species. Fish could have a prolonged shelf life due to the prepared CMR/ADA-CA/CS film. In other words, it may be used as a sustainable food packaging material, with the performance of the film being regulated by different CANE concentrations. [Display omitted] • Schiff base, hydrogen bonding and electrostatic interactions exist in the films. • Cinnamaldehyde nanoemulsions enhanced the film' mechanical and barrier properties. • Cinnamaldehyde improved the film' antibacterial and antioxidant activity. • The trilayer films exhibited a sustained-release effect on cinnamaldehyde. • The films could prolong the shelf life of grass carp fillets during storage. [ABSTRACT FROM AUTHOR]

• Intramuscular connective tissue (IMCT) was mainly degraded in first 10 days. • IMCT degradation was mainly attributed to decorin. • IMCT was hydrolyzed by endogenous collagenase rather than cathepsins. • IMCT and myofibrils (MF) contributed equally to fish texture maintenance. • IMCT failed to protect MF in the process of texture degradation. Although intramuscular connective tissue (IMCT) is low in fish, its impact on texture cannot be ignored due to its special location. Therefore, this study was aimed to investigate the contribution of IMCT degradation to fish softening and its mechanism induced by endogenous proteases. Results showed that IMCT honeycomb-like structure collapsed entirely on the 10th day of ice storage, along with a decrease of shear force by 36.5%. Meanwhile, IMCT and myofibrils (MF) degradation accelerated softening by 25.1% and 15.3% during 10 days of ice storage, respectively. Next, IMCT deterioration was indicated to be highly correlated with decorin degradation (0.956**), followed by elastin (0.928**) and collagen (0.904**). Ulteriorly, endogenous collagenase was shown to degrade IMCT crucial components, while endogenous cathepsins had little effect. In conclusion, this study confirmed that IMCT played an essential role in maintaining fish texture and was mainly degraded by endogenous collagenase. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • Effect of chitosan coating on bacterial composition and quality changes of grass carp was assessed • Lachnospiraceae and Bacteroidaceae were the predominant species in fresh grass carp • Shewanellaceae , Pseudomonadaceae and Flavobacteriaceae became the main microbiota in spoiled samples • Chitosan-based coating effectively inhibited the growth of spoilage bacteria in refrigerated fillets. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 C 5 –C 9 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. [ABSTRACT FROM AUTHOR]

• Chitosan-GTE coating inhibited texture softening of refrigerated fillets. • Lower levels of enzyme activities and proteolysis were shown in coated fillets. • Active coating stabilized proteome of fillets during refrigerated storage. • The down-regulation of structural proteins was effectively retarded after coating. • Protective patterns of flesh texture stabilization by the coating were decoded. 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. [ABSTRACT FROM AUTHOR]

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 H 2 S-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. [ABSTRACT FROM AUTHOR]

The polyelectrolyte complexation between chitosan (CH) and chondroitin sulfate (CS) and the ultrasonication assistance were adopted as the encapsulation strategy for preparing proanthocyanidin (PC) encapsulated nanoparticles (NPs) to protect bio-functions of PC. Conditions of 1.5 mg/mL of CH and CS, 1:3 wt ratio of CH/CS, 0.5 mg/mL of PC, pH 3.25, and 1 min ultrasonic treatment were recommended by the systematic research, respectively, with NPs appearing the smallest size (∼300 nm) and high entrapment efficiency (37.5%). Ultrasound crushed aggregates into nanoparticles by the acoustic cavitation and generated more amide bonds observed by XPS. Due to the physical barrier of NPs, PC in NPs still had a 94.4% DPPH radical scavenging rate after illumination of 10 d. Application of NPs for fabricating CH bio-films was carried out, and the bio-films containing CH/CS-PC NPs decreased aerobic bacteria count and lipid oxidation of fillets stored for 8 d by 2.2 log 10 CFU/g and 51.1%, respectively, which was better than pure CH bio-films. The incorporation of PC-encapsulated NPs to CH bio-films inhibited the bacteria and oxidation induced spoilage for refrigerated grass carp flesh, providing a potential application for food preservation. [Display omitted] • Chitosan and chondroitin sulfate formed nanoparticles to load proanthocyanidin. • Ultrasound reduced the size of particles and created more amide bonds. • The encapsulation for proanthocyanidin maintained the antioxidant effect. • Nanoparticle-contained films enhanced the quality of fish fillets during storage. [ABSTRACT FROM AUTHOR]

• CMCS coating combined with PPE retarded the quality loss of grass carp fillets. • Multifunctional coating retarded texture softening and juice loss of fillets. • The coating inhibited the bacterial growth especially Shewanella. • The carp fillets with CMCS-PPE coating had the refrigerated shelf life of ≥9 days. • Similar performance of the coating was verified in longsnout catfish and snakehead. 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. [ABSTRACT FROM AUTHOR]