Studies On The Enzyme-modification Of Silver Carp Protein And Structures And Functionalities Of The Hydrolysates

The rich fishing resources in China can supply a large of aquatic products,and the total output is growing since the reform and opening up.For a long time,our country freshwater fishery has an important position and role of both at home and abroad.However,due to the perishable,intolerance storage,much little fishbone,heavy fishy smell and other factors,leading to the presence of a very big problem in freshwater fish processing and transportation.Silver carp is one of China's four major freshwater fish which has large output and low price?about 7?/kg?.Currently in the market dominated mostly sold fresh,but the rate of fresh fish corruption up to 30%and the low rate of processing lead an enormous waste of resources.For this reason,strengthening the research of deep processing and comprehensive utilization in order to improve the economic value of freshwater is important.In this study,nutritional value of enzymatic hydrolysis product of silver carp and hydrolysates freezing resistance through applies in freeze-thaw cycles surimi were studied.Silver carp surimi by isopropanol twice degreasing,drying conditions at 40?crushed and sieved to obtain the defatted powder that the fat content is 0.33%,the protein content is 90.74%.The defatted silver carp powder is respectively hydrolyzed by alcalase and protamex for 30min,then the hydrolysis liquid after protease degeneration turn into hydrolysates powder by vacuum freeze-drying.By automatic amino acid analyzer analysis the content of free amino acids and hydrolysis amino acids on the defated silver carp powder and two hydrolysates.The free amino acids content of the defatted fish powder is less than 3.84 mg/g,but alcalase hydrolysates and protamex hydrolysates can reach 13.72mg/g and 62.21mg/g,mean that hydrolysis can generate the free amino acid.The defatted silver carp powder,alkaline protease hydrolyzate and protamex hydrolyzate are similar to the content of hydrolysis amino acids.In addition,essential amino acid content is very rich,respectively,accounting for 36.84%of total amino acids 36.17%and 36.43%.The molecular weight distribution of alcalase hydrolysates and protamex hydrolysates are determined by HPLC.A continuous distribution of peaks show that hydrolysates exist the different peptide molecules weight.According HPLC chromatogram results,elution peaks concentrated on 9min¹4min,elution area were respectively 99.77%and 99.65%,The largest eluting peaks figure of the former in liquid chromatography is corresponding to the molecular weight of 1572.07Da,the latter is corresponding to the elution peak maximum molecular 2027.07Da and 1633.17Da.Using commercial antifreeze?sucrose+sorbitol?as the positive control,studied alcalase hydrolysates and protamex hydrolysates influence on freeze-thaw silver carp surimi related characteristics.Results show that when freeze-thaw cycle number keep increasing,myofibrillar protein Ca²⁺-ATPase activity and content of sulfhydryl is declineng,and the surface hydrophobicity is rising,that confirm appeared frozen denaturation of protein in the process of freeze-thawing cycle.Throughout the freeze-thaw cycle,2%,4%,6%protamex hydrolysates,2%,4%,6%,and commercial alkaline protease hydrolyzate cryoprotectants"4%sucrose+4%sorbitol"the Ca²⁺-ATPase activity decreased by 28.81%,39.19%,41.15%,41.09%,45.68%,46.55%,30.76%,sulfhydryl content decreased by 35.28%,42.64%,47.15%,45.29%,46.12%,51.32%,41.33%,an surface hydrophobicity increase of 2.15,2.26,2.31,2.30,2.36,2.41,2.16.According to the difference variation of physical and chemical properties curves,alkaline protease hydrolysates,protamex hydrolysates and commercial cryoprotectants"4%sucrose+4%sorbitol"have different effect on inhibiting frozen denaturation of protein.Protamex hydrolysates and commercial cryoprotectants overall better than the alcalase hydrolyzate for frost resistance effect,and the different added amount due to the same kind of hydrolyzate also exhibit different frost resistance properties,of which 2%protamex hydrolysates has best performance,followed by commercial antifreeze agent,followed by 4%protamex hydrolysates,while 6%protamex hydrolysates and 2%,4%alcalase hydrolyzate are similar effect,6%alkaline protease hydrolysates frost resistance than the minimum.Then studying the impact of commercial cryoprotectants and hydrolysates on freeze-thaw cycles surimi quality.Through testing surimi gel TPA and observing the microstructure after the 6th cycle of surimi gel,results found that surimi gel hardness and elasticity decreased,and the protein of the components there have been varying degrees of aggregation of denatured.The hardness and elasticity decrease minimum and protein aggregation lesser extent in 2%protamex hydrolyzate group.The same variation trend of other group with previously myofibrillar protein physicochemical properties,further confirmed the previous results.