| Soybean protein isolate as the main research object in this experiment,there were two ways include limited hydrolysis by papain combined with transglutaminase cross-linking treatment or limited hydrolysis after transglutaminase cross-linking were used to modified the SPI. Reveal the mechanism to improve the functional properties of soy protein isolate through both the determination about the change regulation of structure properties [far-UV,circular dichroism CD(Polyacrylamide Gelelectrophoresis)spectra,Raman spectra,intrinsic emission fluorescence spectra analysis and UV-Vis spectra particle, size analysis, SDS-PAGE(Polyacrylamide Gelelectrophoresis polyacrylamide gel electrophoresis) and so on] and the functional properties(dispersibility, emulsifying activity, emulsifying stability and emulsion potential analysis) of soy protein isolate before and after the modification and relationship between them. In addition,The effects on functional properties of myofibrillar protein can be finded by the study on the interaction of modified SPI and myofibrillar protein in the actual production and processing conditions. Moreover, Add the best soy protein isolate samples to sausage to investigate the impact on product quality. In order to lay the theoretical foundation about exploitment of the soy protein isolate specificly used in improvement on meat quality. The main findings are as follows:(1) The protein dispersion index(PDI), emulsifying activity(EAI) and emulsion stability(ESI) of soy protein isolate can be significantly improved( P < 0.05) by Limited degree hydrolysis(DH≤2.0%)combined with transglutaminase cross-linking treatment,especially the DH0.5Cr sample(Hydrolyzate(DH=0.5%)combined with transglutaminase cross-linking treatment)had the maximum( p < 0.05) value. By measuring the structural properties of the modified soy protein,we can find from the far-UV spectra that peak intensity of soy protein isolate by limited hydrolysis combined with transglutaminase cross-linking treatment was increased in the first and decreased later, the peak position moved to a longer wavelength. The tryptopHan fluorescence peak of modified soy protein isolate blue shift and the fluorescence intensity decreased. These phenomena showed that the tertiary structure of modified soy protein isolate changed in a certain degree. Structure became loosed and more tyrosine and tryptop Han were exposed due to protein molecules become unfoded. The results of CD and Raman spectra showed that secondary structureof modified soy protein isolate was changed, α- helical structure reduced, but β-sheet structure increased. The results of size analysis, gel permeation chromatography, SDS-PAGE polyacrylamide gel electrop Horesis showed that particle size of the sample changed and the molecular weight distribution became large. Which indicated that SPI modified by limited hydrolysis combined with transglutaminase cross-linking treatment was aggregated to some extent,and a number of aggregates were generated.(2) The protein dispersion index(PDI), of soy protein isolate can be significantly improved( P < 0.05) by Limited degree hydrolysis( DH≤2.0%) after transglutaminase cross-linking treatment, especially the Cr-DH1.0 sample(Hydrolysis(DH=1.0%) after transglutaminase crosslinking treatment) had the maximum value( P < 0.05), but the EAI and ESI was decteased significantly( P < 0.05), By measuring the structural properties of the modified soy protein,we can find from the far-UV spectra that peak intensity of soy protein isolate by limited hydrolysis after transglutaminase cross-linking treatment was increased in the first and decreased later. The tryptophan fluorescence peak of modified soy protein isolate red shift at first and blue shift later,the fluorescence intensity decreased. The results of CD and Raman spectra showed that secondary structure of modified soy protein isolate was changed, α-helical structure and random coil structure reduced, β-sheet structure increased incordingly. The results of size analysis, gel permeation chromatograp Hy, SDS-PAGE polyacrylamide gel electrophoresis showed that due to the modification by limited hydrolysis after transglutaminase cross-linking treatment, particle size and molecular weight distribution of soy protein isolate were more increased than the samples modified by limited hydrolysis combined with transglutaminase cross-linking treatment. SPI modified by limited hydrolysis combined with transglutaminase cross-linking treatment aggregated to some extent,and more protein molecules larger than 100 KDa were produced.(3) After comprehensive consideration and evaluation, selected DH0.5Cr mixed the myofibril protein according to different protein weight ratio. The changes in the structure and function properties of mixed protein were studied. The emulsifying activity and solubility of mixed protein significantly increased( P < 0.05) with the added amount of DH0.5Cr, but the turbidity of mixed protein significantly decreased(P < 0.05)with the added amount of DH0.5Cr.This may due to myofibrillar protein integrated with modified soy protein isolate and formed some soluble aggregates. In the meanwhile,fluorescence intensity of mixed protein were enhanced. but no significant changes in the peak position. peak position of UV spectrum was red-shifted, peak intensity were weaked with the amount of the DH0.5Cr increased.(4) Adding DH0.5Cr to sausage, with the in Crease of the added amount of DH0.5Cr,cooking loss of products decreased significantly( P < 0.05) than the control and sausage which added the SPI. However,when added amount more than 2%(3% or 4%),the cooking loss did not change significantly(P > 0.05),The value of a* decrease significantly(P < 0.05),but the value of L* increased significantly( P < 0.05).The meat paste added 3% DH0.5Cr had the good emulsifying effect and uniform organization and a solid gel network structure can be formed afterheating. Thereby the hardness, gumminess, chewiness and resilience of product can be improved significantly(P < 0.05). The results of sensory evaluation showed that although the color of sausage added 3% DH0.5Cr was not obviously improved, but flavor, taste and texture were significantly improved, so it has good acceptability.Low-field NMR study showed that two major peaks were founded in T2 relaxation time distribution, T21 and T22 became fast with the added amount of DH0.5Cr increasing, While the peak area A21 increased, A22 decreased significantly( P < 0.05), The relativity analysis indicated that there was a positive relativity between T21 and cooking loss(r = 0.732),and a negative relativity between T21 and hardness(r =-0.5591),but little relativity on gumminess,chewiness and resilience. |
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