Structural And Functional Properties Of Soy Protein Isolate Treated By PH Shifting Combined With Mild Heating And Its Interaction With Myofibril Protein

This study made SPI as the main research object, The SPI was incubated in 0, 1, 3, 5 h in acidic(p H 1.5) solutions at room temperature or in a heated water bath(50°C or 60°C) to induce protein structural unfolding followed by refolding for 1 h at p H 7.0. Discussing the changes and relationship of physi-chemical properties(the total sulfhydryl content and exposed sulfhydryl content), stuctural properties(CD spectra, UV-Vis Spectra, surface hydrophobicity, Intrinsic emission fluorescence spectra, particle size distribution, molecular weight distribution and SDS-PAGE) and functional properties(emulsifying activity, emulsion stability, turbidity, gel strengh) of SPI after various treatments, and revealing the structure-activity mechanism of the improvement of SPI after p H shifting combined with heating treatment. At the same time, futher studied the interaction of modified soy protein isolate and myofibril protein in actual production and processing conditions, revealing the influence of myofibril protein function and gel properties, laying a theoretical foundation of special soy protein that applied to improving meat quality. The main research results are as follows:(1) With the treatments of p H shifting combined with heating, as time lengthening, the total sulfhydryl content and exposed sulfhydryl content decreased singnificantly(P < 0.05), The total SH in native SPI samples was 4.495 μmol/g protein, and the value significantly decreased(P < 0.05) by 22.6, 9.2, 10.18, 45.5 and 80.23% at 5 h for the samples treated with p H 1.5 shifting, 50°C heating, 60°C heating, p H 1.5 + 50°C and p H 1.5 + 60°C, respectively. The heating treatment alone had minimal effect on decreasing the total SH. Thease results revealed that the formation of S-S bonds led to a decreased number of total and exposed SH.(2) CD spectra suggest that the treatment of p H shifting combined with heating led to the losses in α-helical structure content; the results of UV-Vis Spectra, Intrinsic emission fluorescence spectra and the surface hydrophobicity indicated that the side chain of proteins treated by p H shifting combined with heating constantly exposed to the hydrophobic environment; the study of particle size distribution, molecular weight distribution and SDS-PAGE proved that some large molecular weight proteins dissociated into small molecular protein, and produced a few small molecular aggregates, which were mainly dissociated by α′, α and β of ?-globulin.(3) With the results of EAI, ESI, ζ-potential and Microscope photographs, as time lengthening, the emulsifying activity increased singnificantly(P < 0.05), when it was treated over 5h, the EAI increased up to 52.84 m2/g, which was 70% to control, while the emulsion stability decreased singnificantly after increased singnificantly(P < 0.05). ζ-potential increased with holding time and get top to 1.4 fold to control after p H shifting combined with 60°C for 5h. The photoes indicated that the oil droplets became uniform after modifying.(4) The results of gel sthengh and SEM indicated that with the treatments of p H shifting combined with heating, as time lengthening, the gel strengh increased singnificantly(P < 0.05); the sample was improved from 2.11 N to 3.58 N after p H shifting combined with 60 oC heating for 5h, which increased up to 1.7 fold. The structure seem to be tight and meat after modified treatment.(5) After screening, select the p H shifting + 60 oC for 5h sample combined with myofibril protein in different proportions of distribution, and study the distribution of the change of the structure and functional properties of compound protein. The results of UV-Vis Spectra and intrinsic emission fluorescence spectra indicated that the stucture of MPI was partly changed with the ratio of modified SPI:MPI increasing, Tryptophan subsequently exposed; as the ratio of modified SPI:MPI increasing, the EAI decreased after incresaing, the ESI and turbility increased with time; the trend of gel strengh was similar to EAI. Thesas indicated that to improve the physi-chemical properties of MPI, it is necessary to modified the SPI before adding to MPI.