| In this experiment, soy protein and pork myofibrillar protein isolate as the research object. SPI was exposed to a hydroxyl radical-generating system(HRGS) under different H2O2 concentrations(0.1-15 mmol/L) for 1, 3, and 5 h. The protein carbonyl content, bityrosine content and active sulfhydryl content were measured. Oxidized and unoxidized SPI was determined by farUV CD spectra, infrared spectroscopy, tryptophan fluorescence analysis, UV scanning spectra, surface hydrophobicity, particle size distribution, high-performance size exclusion chromatogram and polyacrylamide gel electrophoresis to study the effects of oxidation on SPI structure; on this basis, measuring the effect of oxidation on the emulsification and gel properties(emulsifying activity and emulsion stability, emulsion potential, gel texture, gel color, gel SEM) of SPI, exploring the effect of contact between the impact of oxidation on the structure of soy protein isolate and the impact of functional properties, finally choosing the best functional properties of soy protein isolate by moderately oxidized. Afterwards, myofibril protein isolate and the selected glycosylated soy protein isolate(H2O2 concentration of 1 mmol / L with oxidized 5 h) were mixed according to protein weight ratio 12: 1, 6: 1 and 4: 1. And through the determination of tryptophan fluorescence, turbidity, solubility, emulsifying activity and emulsion stability, gel strength, investigate the effects of moderate oxidation of the functional properties of soy protein isolate myofibrillar protein. The results are as follows:(1)After the oxidation, carbonyl content and bityrosine content of soy protein isolate were significantly increased with the oxidation time prolonged and oxidant concentration increases(P <0.05); the content of the active sulfhydryls was significantly decreased with the oxidation time prolonged and oxidant concentration increases(P<0.05).(2)By measuring circular dichroism and infrared spectra analysis, the result revealed a significantly decrease in α- helix and β- sheet of secondary structure of SPI. Through measuring tryptophan fluorescence, UV scanning and surface hydrophobicity, we found oxidation made soy protein isolate aggregation and the previously exposed tryptophan residues are embedded within the soy protein molecules.The results of particle size distribution and high-performance size exclusion chromatogram revealed that the oxidation process both at the same time along the aggregation and fragmentation, as the process which is dependent on the oxidation degree. By SDS-PAGE electrophoresis results can be found that β-conglycinin more vulnerable than glycinin hydroxyl radical, while the oxidized soy protein isolate was aggregate by disulfide bond.(3) The potential, photographs, emulsifying activity, emulsion stability of the emulsion were analysised, emulsifying activity and emulsion stability of soy protein isolate oxidation showed a downward trend after the first increase, the emulsifying activity index reached the maximum value(P<0.05), at the concentration of 1 mmol /L with 5 h. Combining gel strength, gel color and gel SEM results, after oxidation the gel strength of soy protein isolate was showing a downward trend after the first increase. When moderately oxidized help improving the gel strength, excessive oxidation damage the gel strength.(4)After comprehensive consideration and evaluation, myofibril protein isolate and the selected glycosylated soy protein isolate(H2O2 concentration of 1 mmol / L with oxidized 5 h) were mixed according to protein weight ratio 12: 1, 6: 1 and 4: 1.Then investigate the effects of moderate oxidation of the functional properties of soy protein isolate myofibrillar protein. Effects of moderate oxidation SPI on fluorescence, UV spectra and turbidity of myofibril protein isolate: by measuring tryptophan fluorescence spectra, UV spectra and turbidity shows that the structure of complex protein complex appearing some changing. This may be due to initially myofibrillar proteins can be combined to form a stable system with moderately oxidized soy protein isolate, but with the increase amount of modified soy protein isolate added upset this balance. Effects of moderate oxidation SPI on functional properties of myofibril protein isolate: complex protein emulsifying activity and solubility were increased first and then declined trends with increasing amounts of oxidized soy protein isolate. The gel strength of the composite protein was significantly increased with increasing amounts of soy protein isolate(P <0.05). |
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