Coating of gelatin and chitosan can improve fish fillet’s quality, but the mechanism is not clear. Chitosan/gelatin coatings significantly prevented deterioration of golden pomfret fillet at 4 C. Chitosan with 7.2% gelatin group showed the best effect on preserving the length of myofibril, which remained greater than 15 lm at day 17 of storage, while for control, chitosan and chitosan combined with 3.6% gelatin group, it was 5.03, 10.04 and 9.02 lm, respectively. The MALDI-TOF MS result revealed that the coatings slowed down the protein deterioration of fillet. On days 13 and 17, the myosin light chain and myoglobin in control group degraded, while the two proteins still existed in chitosan/gelatin coated groups. Overall,the chitosan with 7.2% gelatin coating had the best effect on preserving fillet’s quality during storage.The coating may exert its protective effect via inhibiting myofibril degradation within fillet.

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本文研究了植物乳杆菌6003活细胞（ell）、细胞裂解液（ell extracs，CE）以及两者混合液（ell+CE）对肌原纤维提取液中的蛋白质的分解作用。通过蛋白质、肽、游离氨基酸分析，表明各实验组对肌原纤维提取液中蛋白、肽分解、游离氨基酸的增加作用较弱，其中Cell+CE组中作用稍为显著，CE组对肌原纤维提取液中蛋白质的分解几乎不起作用。

目的 研究死后机体骨骼肌肌原纤维小片化指数（MFI）与死亡时间之间的关系。方法 双缩脲法测定室温下不同死后时间家兔骨骼肌全蛋白浓度，分光光度法测定540nm处0.5mg/mL蛋白浓度下的骨骼肌肌原纤维小片化指数。结果 在死后早期，肌原纤维小片化指数随着时间延长逐步增高。结论 肌原纤维小片化指数可用于早期死亡时间的推断。

The present study studied the effects of fish gelatin (FG) incorporated with grape seed extract (GSE) through vacuum impregnation (VI) on refrigerated tilapia (Oreochromis niloticus) fillets over 12 days. The VI of FG-GSE significantly improved the quality of the fish by decreasing drip loss, texture changes, and microbial survival. It also delayed protein oxidation by inhibiting the formation of disulphide bonds and carbonyl groups, and maintaining a higher sulfhydryl content and Ca2+-ATPase activity. Regarding myofibril degradation, FG-GSE maintained their secondary structure by increasing the ratio of α-helices and β-sheets (70.88–75.51%). Atomic force microscopy further revealed that the FG-GSE coating preserved the myofibril nanostructure by maintaining their length, width, and height. Overall, the synergistic effects of VI with 3% FG and 0.9% GSE suggested a promising approach for fillet preservation.

Bromelain was used to tenderize golden pomfrets (Trachinotus blochii). The enzyme kinetic model was x=2.447×ln[1+(1332.21×E0S0-1.74)t], which indicated that the degree of hydrolysis (DH, x) was dependent on hydrolysis time (t), the initial concentration of myofibril (S0 ) and bromelain (E0 ). The relationship between the overall hydrolysis rate (v), S0 , E0 , and t is demonstrated as: v=(16.50(E0S0)-1.33)S0 exp {-2.447ln[1+(1332.21E0S0-1.74)t2]}. Sample of 0.40% E0 /S0 was further used to study the effects of hydrolysis time on the changes of proteins, peptides, free amino acids (FAA), and protein nanostructure. SDS-PAGE result showed that myosin heavy chain was degraded dramatically from 22.88% before treatment to 12.03% after 2 min bromelain treatment. Meanwhile, bromelain did not exhibit activity towards actin, trypomyosin, myosin light chain, and troponin C. A general increase of amino acids indicated the increased DH and the preferential cleavage sites of bromelain in the descending order of lysine, glutamic acid, glycine, ornithine, methionine sulfoxide, and alanine. Atomic force microscope images showed that the strip-like structure of myofibril was considerably degraded by bromelain, and the granulation of protein after 20 min indicated possible self-assembling of protein hydrolysate. Confocal laser scanning microscopy further confirmed the degradation of myofibril proteins and formation of protein aggregates.

An enzymatic method to tenderise golden pomfret (GP, Trachinotus blochii ) flesh by marinating with bromelain (BML) solution was developed to produce GP fish balls with a texture similar to those of yellowtail fusilier (YF, Caesio cuning ). Treatment with BML reduced the hardness, chewiness and gel strength significantly but increased the resilience of GP fish balls. As a result, 0.4% (enzyme-substrate ratio, w / w ) BML-treated GP fish balls had the same texture properties as YF fish balls. Meanwhile, changes in myofibrillar proteins in the fish balls were determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry and atomic force microscopy. The results indicated that BML degraded myosin light chain and troponin T effectively, without affecting actin. BML treatment generated protein fragments with significantly smaller sizes, thereby improving the tenderness of the flesh. The length, width and height of the myofibrils from 0.4% BML-treated fish ball were 6.42, 1.52 and 1.48 μm, respectively, which were not significantly different from the myofibrils of YF fish balls, indicating that the similar nanostructure determined the comparable texture properties. Gas chromatography-mass spectrometry analysis showed that 0.4% BML decreased the amount of hexanal, hexadecane, 1-octen-3-ol and 2,6,10,14-tetramethylpentadecane but increased the ratio of heptadecane from 18.14 to 38.23% in the treated fish balls, making the flavour of 0.4% BML-treated GP fish balls similar to that of YF balls. Overall, the results suggest that 0.4% BML-tenderised GP could be a promising alternative to YF to produce quality fish balls.

The effect of fish gelatin addition on mass transfer, nutrient loss, texture and nanostructure of fish balls was investigated. Mass transfer models were built and the root-mean-square-errors were 0.1432, 0.3178 and 0.1000 for exponential, power-law and linear models, respectively. After gelatin addition, the mass transfer coefficient/model parameter and moisture content increased, and the hardness and chewiness of fish balls decreased. Myofibrils were imaged using atomic force microscope (AFM). The length of the myofibrils was greater than 15 μm before and after boiling for 10 min; however, they decreased to around 14 and 11 μm after 20 and 30 min boiling, indicating degradation of myofibrils. Meanwhile, there was no significant difference among different groups, suggesting that the added gelatin did not affect the nanostructure of the fish balls. Furthermore, increasing gelatin addition resulted in fewer water-soluble proteins and peptides in the boiling water. The results suggest that added gelatin increased the mass transfer coefficient/model parameter by increasing the moisture content and decreasing the nutrient loss. It also improved the texture by decreasing the hardness and chewiness, and did not affect the nanostructure of fish ball myofibrils.

Microbial, physicochemical, rheological, and microstructural changes of surimi prepared by pH shift methods and the traditional water-washing method during cold storage were investigated. The starting aerobic mesophilic count (AMC) of pH shift surimi was around 1 log CFU/g lower than water-washed surimi, suggesting antimi- crobial effects of the pH shift. All samples could be stored for 5 to 6 days based on the AMC results. Throughout count (AMC) of pH shift surimi was around 1 log CFU/g lower than water-washed surimi, suggesting antimi- crobial effects of the pH shift. All samples could be stored for 5 to 6 days based on the AMC results. Throughout the storage, the gel strength of alkaline-treated surimi increased from 204.2 to 491.9 g, while water-washed surimi decreased from 462.1 to 172.9 g. After the storage, alkaline-treated surimi showed lower total volatile basic nitrogen (TVB-N) value and smaller network hole size that was suitable for incorporation of moisture and starch. It also remained its rheological properties comparing with acid-treated surimi, with better odour prop- erties, less protein degradation, and better network formation. The results indicate that alkaline-treated surimi is more suitable for cold storage.