A Study Of Different Soy Protein Gel Structure Under Low PH

In recent years,the international community s research about the heat-induced proteins self-assembly into amyloidal-like fibrils at low pH, low ionic strength conditions, especially animal protein are very much. Ackerman’s studies the soy protein isolate and11S globulin profiled, the length and thickness of the linear aggregates at low ionic strength, low pH; Tang et al reported the formation of the11S and7S fibers heat-induced self-assembly, fibrosis self-assembly found in7S aggregate formation was stronger than11S. However, under acidic conditions, research on the gel properties of soy protein aggregates also rarely reported.This paper studies the aggregate type of heat-induced gels of various components soy proteins at low pH,analysis of the characteristics of different types of gels (rheological behavior, textural properties) and observed the microstructure of gels by scanning electron microscopy, and the main force (hydrophobic surface, free sulfhydryl groups), analyzing and comparing the two types of gels’ reversibility, including acid reversibility and mechanical reversibility. By the detecting and anglicizing of the several characteristics, provide some theoretical guidance and basis for the soy protein gels’ applications in food production. The main findings are as follows:Aggregation type of the gels By heating different protein samples from pH1.5to pH6.0(soluble whole protein,7S,11S, acidic subunit, basic subunit) and direct observant of an apparent aggregation state, we determined its research range of pH<4, through the TEM image analysis, we divided the protein gel to particulate gels (pH3.5) and the fine stranded gels (pH2.0), and the pH values of these two gel as the focus of the study. Polymerization of the gel at pH3.5is in particulate form, the short tufted; polymerization of the gel at pH2.0is a linear thin flexible long-chain, in particular acidic subunit and7S, most obvious.The characteristics and the microstructures By measuring the rheological and textural properties of different gels, we found for five different protein components, the rheological properties of the fine stranded gels should be weaker than the particulate gels, and the hardness, stickiness, chewiness, also weaker than the particulate gels, elastic a little stronger. The7S gels hardness is the worst in the various protein fractions. Through the scanning electron microscopy images, we found that compare to the structure of the gel at pH2.0, the structure of gel at pH3.5should be dense, have small and uniform porosity, more regular network structure, and thus the hardness,viscosity,chewiness and other characteristics of the particulate gels are stronger than the fine stranded gels at pH2.0. The greater density of the structure can also lead to the elastic relatively smaller.7S and acidic subunit of the two proteins at different pH values forms the gels microstructures’ difference is the most obvious. The main forces By measuring the surface hydrophobic and the free sulfhydryl groups of different protein components of protein gel at pH1.5, pH2.0, pH3.0and pH3.5,we found that the surface hydrophobic of soluble whole protein,7S and11S, in the first hours’ heat treatment, achieve the maximum, and the subsequent heating process, the surface hydrophobic decreased. For the acid subunits and basic subunits, during heating, the surface hydrophobic still decreased and pH1.5> pH2.0> pH3.0> pH3.5. The free sulfhydryl groups, in the whole heating process has been showing a downward trend and pH1.5<pH2.0<pH3.0<pH3.5. Compared to the two kinds of gels, the main force of the fine stranded gels is surface hydrophobic, the main force of the particulate gels is disulfide bond.Reversibility The acid reversible of5kinds of protein samples, the gel samples at pH2.0than the gel samples at pH3.5restored to a large extent, especially to be noted that the7S and acid subunits in the fiber structure at pH2.0restorative particularly, to95.56%and81.02%. May be this structure have a better reversibility. Compared to the two types of gels, the mechanical recovery at pH2.0is slightly higher than at pH3.5.