Effect Of Mixed Vegetable Proteins On Rheological Properties And Microstructures Of Surimi

Using vegetable proteins(VP)and other macromolecules(e.g.,polysaccharides,or animal proteins)to form functional complexes is considered as a method to improve the functionalities of vegetable proteins.In these multi-component food systems,the interactions between vegetable proteins and other components will unavoidably take place in a variety of ways,which potentially have great influences on the structures and properties of these products.In this paper,rheological and gel properties of pure vegetable protein solutions(e.g,soy protein isolated(SPI),peanut protein isolated(PPI)and rice protein isolated(RPI)),interactions between different vegetable proteins(SPI+PPI,SPI+RPI and PPI+RPI)and the influence of VP mixtures on rheological properties and microstructures of myofibrillar protein(MP)gels and surimi were studied.The results were as following:1.VP mixtures could form gels under appropriate conditions(e.g.concentration,temperature,pH and ionic strength).The minimum concentrations for gel formation of SPI+PPI,SPI+RPI,and PPI+RPI(1:1,w/w)were 14%,10%and 12%,respectively.The addition of low concentration sodium chloride(0.1 M or 0.3 M)at pH 2.0 or 9.0(far away from pI)was helpful to form gel with higher storage modulus(G')compared to the addition of high concentration sodium chloride(1.0 M)at pH 7.0.The results of strain,frequency and shear rate sweeps of mixed VP gels showed that the gel strength decreased in this order:SPI>PPI,SPI+PRI(SP),PPI+RPI(PR)>SPI+RPI(SR)>RPI(14%,pH 7.0,0.5 M NaCl).Molecular driving forces involved in mixed VP gels were mainly hydrophobic interactions and disulfide londs.However,there was no evidence showing that reactions took place between different VP from the SDS-PAGE electrophoresis and SEM perspectives.However,interwoven structure had formed between different VP gel network structures.2.When the additional level of mixed plant proteins was 2%,the impacts on the gel strength of mixtures turned out to be insignificant or adverse.With increasing addition level from 6%to 14%,the gel strength of mixtures increased,because a greater proportion of the dissimilar biopolymers(i.e.,proteins)remained in close proximity producing a more interdigitated network and hence higher G' values.Molecular driving forces involved in mixed VP-MP gels were mainly hydrophobic interactions and disulfide bonds.However,there was no evidence showing that reactions took place between VP and MP from the SDS-PAGE electrophoresis and SEM perspectives.However,interwoven structure had formed between MP and VP gel network structures.3.Adding a small amount of mixed VP(about 2%)could significantly increase the gel strength of surimi-VP mixtures.Molecular driving forces involved in mixed surimi-VP gels were mainly hydrophobic interactions and disulfide bonds.However,compared with MP gels,nonspecific associations involved in surimi and surimi-VP gels increased.In addition,there was no evidence showing that reactions took place between surimi and VP from the SDS-PAGE electrophoresis and SEM perspectives.However,interwoven structure had formed between surimi and VP gel network structures.4.The addition of SPI and PPI into surimi induced a decrease in the hardness,gumminess and chewiness of gels,but there were no differences in springiness and cohesiveness.And the effect of RPI was the opposite.So the addition of SPI+PRI and PPI+RPI into surimi could increase the hardness,gumminess and chewiness of mixed surimi-VP gels.In addition,those mixed gels containing SPI and PPI showed the increases in water holding capacity(WHC),but the impact of RPI turned out to be adverse.While the WHC increased significantly when mixed plant proteins were incorporated.Futhermore when SPI and PPI were added,mixed gels showed a significant decrease in whiteness,but there was no difference after adding RPI.So the addition of SPI+PRI and PPI+RPI into surimi could offset the negative impact of SPI and PPI on the whiteness.All above results indicated that although SPI,PPI,RPI,MP and surimi could not react with each other,an interwoven structure had formed under appropriate conditions(e.g.concentration,temperature,pH and ionic strength).Meanwhile,results of this research have certain reference significance on the application of mixed VP into surimi products.