Cryo-protective Effect Of Soybean Oligosaccharide On Freshwater Surimi And Its Mechanism

Surimi is usually stored and circulated under freezing conditions.Frozen storage will cause the freezing denaturation of myofibrillar protein,the main component of surimi protein,which will lead to the decline of gel properties,emulsification properties and water holding capacity of surimi protein,resulting in inferior quality of surimi products.Adding cryoprotectant is one of the effective ways to delay the frozen denaturation of protein.Nowadays,the commercial cryoprotectant "4%sucrose-4%sorbitol" will bring excessive sweet taste and heat to the surimi products.It is an urgent problem to find an effective cryoprotectant with "low sugar and low heat" in the production of frozen surimi.Soybean oligosaccharide is a potential cryoprotectant,but its freezing protective effect and its mechanism on surimi remain unclear.Therefore,this project takes grass carp surimi as the research object to study the influence of soybean oligosaccharides on the stability of frozen surimi storage,and analyzes the effect of soybean oligosaccharides on the structure of myofibrillar protein and water phase transformation during frozen storage,to provide theoretical reference for the application of soybean oligosaccharides in frozen aquatic products,in particular with frozen surimi.The main results are as follows:The influence of the addition of soybean oligosaccharides on thawing loss of surimi during frozen storage was studied,as also the gel strength,water holding capacity,whiteness,water distribution,and sensory quality of surimi gel.by adding 6%～8%soybean oligosaccharides.After 120 days of frozen storage,the gel strength,water holding capacity and whiteness of surimi with 8%soybean oligosaccharides and commercial antifreeze agent decreased by 34.48%and 30.44%,4.12%and 3.11%,9.96%and 9.81%,respectively,and the thawing loss was 0.63%and 0.56%,respectively.The addition of 8%soybean oligosaccharide and commercial cryoprotectant could inhibit the decline of the sensory quality of surimi and improve the sensory quality of surimi gel.The 8%soybean oligosaccharide has comparable antifreeze effect to commercial cryoprotectant for surimi and is more advantageous in maintaining the whiteness and sensory quality of surimi gel.The effects of soybean oligosaccharides on the denaturation and structure of the myofibrillar protein of surimi during frozen storage at-18℃ for 120 d were studied.The results showed that 8%soybean oligosaccharide could inhibit the freezing denaturation of surimi protein during freezing storage.After 120 days of frozen storage,salt-soluble protein content,Ca2+-ATPase activity,total sulfhydryl group content,active sulfhydryl group content and α-helix content of myofibrillar protein,which is 8%soybean oligosaccharide group and commercial antifreeze group,decreased by 58.55%and 67.65%,88.50%and 91.29%,50.72%and 63.98%,61.69%and 66.25%,respectively.Surface hydrophobicity of 17.53%and 15.20%increased by 41.34%and 44.79%,significantly lower than that of the control group.The fluorescence intensity of tryptophan and tyrosine decreased by 32.97%,24.60%and 29.54%in 6%and 8%soybean oligosaccharide groups and 29.45%,28.64%and 25.95%in commercial antifreeze groups,respectively,after frozen storage for 120 days.The addition of 6%～8%soybean oligosaccharides can effectively stabilize the protein structure and inhibit the frozen degeneration of myofibrillar protein during freezing storage.The effects of soybean oligosaccharide addition on water distribution and water phase transformation of surimi during freezing were studied.The results show that the lower the freezing temperature,the lower the freezing point of surimi,the faster the freezing rate,and the shorter the time through the maximum ice crystal zone.The commercial cryoprotectant and 6%～8%soybean oligosaccharide groups exhibited insignificant differences in freezing point and the freezing rate when the frozen temperature was the same.The binding water content of surimi with the addition of the 8%soybean oligosaccharide and commercial cryoprotectant was 11.82%and 13.77%,respectively.The addition of soybean oligosaccharides can increase the bound water content in surimi,shorten the time for surimi to pass through the maximum ice crystal zone during freezing,reduce the freezing point of surimi and the formation of ice crystals and inhibit the freezing denaturation of surimi.