热处理对大豆分离蛋白结构和凝胶性的影响

Effect of Heat Treatment on the Secondary Structure and Gel Property of Soybean Protein Isolate

通过对大豆分离蛋白(soybean protein isolate,SPI)的亚基组成及结构、自由氨基浓度、游离巯基含量、表面疏水性及凝胶强度的测定,研究热处理对SPI理化性质、结构特性及凝胶特性的影响。研究表明,随着热处理温度的升高,SPI亚基解离加剧,SPI的β-折叠含量明显下降,无规卷曲含量显著增加。当热处理时间为10 min、温度从70℃提高到95℃时,SPI中自由氨基浓度、自由巯基含量及表面疏水性呈上升趋势,SPI形成凝胶的强度先升高后降低,凝胶失水率呈下降趋势。当热处理温度为90℃,随着时间从5 min延长到60 min时,SPI中自由氨基浓度不断增加,自由巯基含量及表面疏水性则先增加后降低,SPI形成凝胶的强度呈上升趋势,凝胶失水率呈下降趋势。随着凝胶保温时间的延长和温度的提高,SPI凝胶的强度均不断提高,失水率均不断下降。综合考虑,制备SPI凝胶的最佳条件为:热处理90℃、15 min,保温90℃、30 min。

This study determined the subunit composition and structure, free amino group content, free sulfhydryl content, surface hydrophobicity index and gel strength of soybean protein isolate （SPI）. Furthermore, the effect of heat treatment on physicochemical properties, structural characteristics and gel property of SPI was explored. The results showed that with the increase in heat treatment temperature, the subunit dissociation of SPI was aggravated; the β-sheet content decreased signifcantly, whereas the random coil content increased signifcantly. The free amino group content, free sulfhydryl content, and surface hydrophobicity tended to increase with elevated temperature from 70 to 95 ℃ when the heat treatment lasted 10 min. In addition, the gel strength of heat induced gel decreased after an initial increase, and its water loss continuously dropped. In the case of heat treatment at 90 ℃, the free amino group content gradually increased, and the free sulfhydryl content and surface hydrophobicity initially increased and thereafter declined with increasing the treatment time from 5 to 60 min; the gel strength and the water loss of heat induced gel increased and declined, respectively. The gel strength and the water loss gradually increased and decreased respectively with the increase in temperature and holding time. To sum up, the optimal conditions to obtain SPI gel should be heat treatment at 90 ℃ for 15 min, and then maintenance at 90 ℃ for 30 min.