Research On Frozen Denaturation Mechanism Of Silver Carp (Hypophthalmichthys Molitrix) Surimi Protein And Application Of Cryoprotectants

Silver carp （Hypophthalmichthys molitrix） is one of four major cultured fishspecies in China, which has rich volume of production and nutrition. Silver carpcould be usesd as a good material for freshwater surimi processing, due to its lowprice, quick growth and white flesh.Considering the influence of harvest season, the silver carp surimi is usuallypreserved at a low temperature, but the protein of surimi is not stable during frozenstorage, which will influence later processing performeance seriously. In this paper,the frozen denaturation of silver carp surimi at different temperatures wasinvestigated, taking salt dissolved protein content, pH value, total sulfhydrylcontent, gel strength, Ca²⁺_-ATPase activity and so on as indexes. Combined withthe traditional cryoprotectants, orthogonal experiment was designed to study thenew combination of cryoprotectant and its anti-freeze stability, in order to achieve“low-sweet, low-calorie”. The goal of this work is to provide theoretical support forfrozen surimi preservation and its further research.Based on the nutrition analysis of silver carp surimi, the content of lipid andash in surimi declined compared to that in fish muscle, and the content of proteinincreased relatively. Myofibrillar protein was the major protein, contained thehighest of the total. Silver carp surimi contains eight essential amino acids for adulthuman beings, with higher levels of glutamate （Glu）19.87%, aspartic acid （Asp）10.85%and lysine （Lys）10.61%.During the frozen storage at-4℃（partial frozen storage）,-20℃（lowtempreture frozen storage） and-40℃（cryopreservation）, surimi protein wasdegenerated at different degree levels. With the extension of frozen storage period,the salt dissolved protein content, pH value, Ca²⁺_-ATPase activity, total sulfhydrylcontent, gel strength and whiteness decreased, while disulfide bond contentincreased, and the lower frozen storage temperature is, the less extent of frozendenaturation of surimi protein is. The differential scanning calorimetry （DSC）result showed the higher frozen storage temperature, the lower transformationtemperature and enthalpy value are, while the changes of actin were notsignificantly. By the analysis of circular dichroism （CD）, low temperature frozen can make protein secondary structure from natural α-helix to random coil, and thelower storage temperature can slow down the decrease in α-helix content. Byscanning electron microscope （SEM）, it was known that higher frozen storagetemperature makes protein aggregation tends to clutter and loose texture, which isno longer dense and smooth, losing rounded and full texture characteristics of freshsurimi gel.By single factor and orthogonal experiments, the optimum formula of fourkinds of antifreezes for preventing the frozen denaturation was: trehalose4%,sucrose1%, sorbitol2%, lactitol3%, the sweetness of new cryoprotectant is lowerthan that of commercial blend and the cryoprotective effect is also better, andachieve the goal of “low-sweet, low-calorie”.By the experiment of anti-freeze stability, all index values of the newcompound antifreeze group were slightly higher than those of the commercial blendat the same storage time, and the decreasing amplitude of the index values wassmallest at the end of frozen storage, which showed that new cryoprotectant canwell prevent the freeze denaturation of surimi proteins.