Functional Modification Of Silver Carp Myofibril Protein By Enzymatic Hydrolysis And Membrance Separation

Silver carp is one of four major Chinese carps,for the charcateristic of quick growth,less diseases,high yield and low cost of breeding,it is one of fish farmers'favorite fingerling.Both the farming area and quantity are in the forefront.And the annual output is second only to grass carp,which accounts for 15%of freshwater fish resources.But its application is restricted in food process industry due to the unsatisfactory functional properties,which was major made into surimi.In order to improve the functional properties of silver carp myofibrilar protein,enzymolysis and membrane separation technologies were studied in this paper to explore a feasible modification method.The main results were as follows:(1)Trypsin,neutral protease,alkaline protease and compound enzyme were adopted to limited hydrolyze silver carp myofibrillar protein,the degree of hydrolysis(DH)and functional properties during the hydrolytic process were studied.The results showed that:during the hydrolytic process,the degree of hydrolysis was under 5%,the modified protein molecular weight is about 20 kDa,the length of myofibri was shorten,and emulsibility and foamability exhibited a trend of increased firstly and then decreased.The protein modified by trypsin exhibited wonderful emulsifying actibity(57.3 m~2/g)and emulsifying stability(46.6 min),which was about three-fold of natural protein.While the protein modified by neutral protease showed excellent foamability(104%)and foaming stability,which is nearly eleven time as much as natural protein.The protein modified by compound enzyme show both good emulsibility(65.5 m~2/g,27.6 min)and good foamability(110%).(2)Silver carp myofibrillar protein limited hydrolysis by trypsin was conducted to improve myofibrillar protein solubility.During the process,molecular weight distribution,existing forms of nitrogen,size distribution and surface hydrophobicity were studied to prevent excessive hydrolysis.The solubility of modified protein under different pH,ionic strength and temperature were investigated.The results showed that:under the codition of 1250 U/g,pH 8.0,50°C,the protein hydrolysed for 80 min has a average molecular weight of 10 kDa,which is the boundary of protien and peptide and is proved to owe excellent solubility,as well as fine emulsifying properties and foaming properties;the modified protein showed wonderful solubility in neutral and alkaline environment of more than 80%;the lowest solubility appear at pH 5.0(67.4%);under the salting strength of 0.1 M-1 M,the solubilty remained above80%;after heat treatment by PAP,100°C,121°C,the thermal stability remained above 80%.(3)The effects of two kinds of modification methods on the functional properties of enzymatic hydrolysis and the membrane separation process step-wise modification were compared with that of the enzymatic hydrolysis-membrane separation.The results are as follows:among the three components of the two types of modified,2 kDa showed the best emulsifying activity and foaming,2 kDa through the liquid showed the best emulsion stability.But compared to the former,the content of2-10 kDa component in the enzymatic hydrolysis-membrane separation coupling modification is higher,and the functional properties of 10 kDa is also better.So it is more effective to improve the functional properties of protein by using the method of enzyme hydrolysis-membrane separation coupled with 2500 U/g.