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In this study, silver carp scale antifreeze peptides (ScAFPs) were prepared by enzymatic hydrolysis. Taking the freeze-thawing survival rate of Streptococcus thermophilus as the main index and the degree of hydrolysis as the auxiliary index, the optimal enzymolysis preparation process of ScAFPs was obtained through single factor and response surface optimization. At the same time, the basic properties of ScAFPs and their influence on the gel stability of surimi were studied. The results showed that the selected enzyme preparation was trypsin, substrate concentration of 5.0%, enzyme dosage of 3.8%, enzymolysis temperature of 37 ºC, enzymolysis time of 3.5 h. Under these conditions, the frozen survival rate of ScAFPs against Streptococcus thermophilus was 82.19%±1.03% and the degree of hydrolysis was 7.54%±0.43%. The relative molecular weight of ScAFPs was mainly in the range of 180~3000 Da, and its isoelectric point was around 4.2. Moreover, ScAFPs had strong hydrophilicity and good thermal stability, which could effectively reduce the ice crystal content in the system. The effect of ScAFPs on gel properties of freezing-thawing surimi showed that after five freezing-thawing cycles, the decrease of gel whiteness, hardness, chewiness and gel strength of surimi treated by ScAFPs was significantly (P

To study the changes of hairtail meat and its surimi under different frozen conditions. Fresh hairtails were stored at −7, −13, −18 and −23 ℃ for 15~120 d, respectively. And the physicochemical properties (carbonyl group, sulfhydryl group, Ca2+-ATPase activity, TBARS) of fish meat and the gel properties (color, gel strength, water holding capacity, microstructure) of surimi were determined at different stages. The results showed that with the extension of frozen time, the carbonyl content and TBARS value increased, while sulfhydryl content and Ca2+-ATPase activity decreased. For surimi gel, the color gradually deteriorated, and the water retention capacity gradually decreased. The lower frozen temperature, the smaller changes in each group. No spoilage occurred in the samples except the fish meat whose TBARS value was greater than 0.58 mg MDA/kg after being frozen at −7 ℃ for 60 d. After 120 d, the gel strength of surimi in four temperature groups decreased by 72.33%, 54.13%, 39.17% and 29.31%, respectively. SEM showed that the surimi had better three-dimensional network structure at lower frozen temperature. In conclusion, longer frozen time reduced the quality of hairtail meat and the gel properties of surimi, while lower temperature could inhibit the deterioration process.

Taking soybean mixed allergens as the target, a sandwich-enzyme linked immunosorbent assay and an indirect competitive enzyme-linked immunosorbent assay for the rapid and convenient detection of soybean allergens were established. The two methods were compared through the recovery experiment of actual processed samples, the recovery experiment of spiked food and the detection of real food samples, and their respective application scopes were determined. Sandwich ELISA method, the standard concentration was in the range of 0.0078~30 μg/mL, showing a good linear relationship, the curve equation was y=0.2333x+0.0692 with coefficient of determination R2=0.995. The detection range of the competitive ELISA method was 10~100000 ng/mL, and the lowest detection limit was 10 ng/mL. The recovery rate of orange juice after sandwich ELISA was higher than that after competitive ELISA, reaching more than 100%. For chocolate, beef sauce, bread and cake with complex ingredients and processing methods, the recovery rate after competitive ELISA was higher than that after double-antibody sandwich ELISA. In the detection of soybean allergens in fermented foods, the concentration detected by competitive ELISA was higher than that detected by sandwich ELISA, while in the detection of simple ingredients such as sesame paste and soy milk, the concentration detected by sandwich ELISA was slightly higher than that detected by competitive ELISA. In general, the competitive ELISA method was more suitable for the food with complex food matrix and deeply processed, while the sandwich ELISA method was more suitable for the food with simple food ingredients and lightly processed food, both of the two methods can achieve more accurate detection in their respective application scope.

Freeze denaturation during frozen storage is one of the main reasons for the decreased gelation ability of surimi after thawing. The myosin heavy chain (MHC) is the major contributor to the formation of surimi gel. In this study, the antifreeze peptides were prepared by hydrolysis of different enzymes and screened by computer simulated enzymatic hydrolysis technology. The spatial structure of sea bass myosin was constructed by protein homology modeling. The action sites and possible mechanism of sea bass myosin heavy chain with antifreeze peptides were analyzed by molecular docking and molecular dynamics simulation techniques. The results showed that the trypsin hydrolysates possessed high antifreeze activity, which the survival rate of bacteria was 80.35%±4.39% after freeze-thaw cycle, and had thermal hysteresis and ice recrystallization inhibition activity. The peptides GPR and GPAGGK obtained by simulated trypsin enzymolysis could combine with the myosin heavy chain by intermolecular force, and the binding of peptide GPAGGK to myosin was more stable. This binding could block the myosin structural changes in response to temperature change. The mechanism might be that the antifreeze peptides combine with the structural cavity of the myosin heavy chain, which affected the formation of hydrophobic bonds and disulfide bonds caused by the dissociation of the bound water. Thus the aggregation of protein side chains, structural changes and ice crystal displacement were impeded, which was conducive to the quality maintenance of surimi and surimi products in cryopreservation. This study would provide a theoretical basis for the application of antifreeze peptides in the quality maintenance of surimi and its products during frozen storage.

In order to study the effect of freeze-thaw cycle on quality of surimi under different low temperature conditions, the prepared surimi samples were divided into 3 groups and placed in the refrigerator at 4, −18, −35 ℃, respectively. Five repeated freeze-thaw cycles were simulated. Different indexes, such as rheological characteristics, gel properties, water changes (low field nuclear magnetic resonance (LF-NMR), freezing loss, thawing loss, cooking loss rate, water holding capacity (WHC)), texture characteristic, were analyzed, which also combined with the microstructure observation, so as to assess storage temperature influence on the quality of minced fish during freeze-thaw cycles comprehensively. The results showed that the storage temperature and freezing-thawing cycle were important factors affecting the quality of surimi. The lower the storage temperature was, the less the quality of surimi changed. With the increase of the freezing-thawing cycle, the viscosity of surimi gel decreased, G' and G" decreased, and tanδ increased, and the hardness, chewiness, gel strength decreased first and then increased. The freezing loss and thawing loss were 2.18% and 22.87%, 2.38% and 10.20% at −18 ℃ and −35 ℃ for 5 cycles, respectively. The WHC of surimi decreased from 80.04% to 73.51% and 75.33%, respectively. The results of this study can provide theoretical reference for quality maintenance of surimi and its gel during circulation.