Effects of pH on Structure and Emulsibility of Catechin-Soy Protein Isolate Complex(pH值对儿茶素-大豆分离蛋白复合物结构与乳化性的影响)
摘要
Soy protein isolate (SPI) was used as raw material to prepare protein complexes loaded with catechins under different pH conditions. The interaction mechanism was explained by analyzing thermal stability, fluorescence quenching type, binding site number, thermodynamic parameters, and secondary structure content by differential scanning calorimetry, ultraviolet-visible spectroscopy, fluorescence spectroscopy, and circular dichroism spectroscopy. The binding affinity between catechin and SPI, and the emulsibility of the complexes were analyzed. The results showed that fluorescence quenching type of catechin on SPI under different pH was static quenching. Electrostatic interaction was the main force between catechin and SPI when treated under pH 3.5,5.5 and 6.5. Additionally, hydrogen bonds and van der Waals forces were the mainly intermolecular forces for the complex under pH 4.5. Moreover, hydrophobic interactions played major roles in the interaction between catechin and SPI at pH 7.0,7.5,8.5 and 9.5. The thermal stability of the complex gradually increased with the increase of pH value. Furthermore, the SPI denaturation temperature of complex increased to 157.09℃ at pH 9.5. The emulsifying activity and emulsion stability of the complex at pH 7.5 were 7.70% and 13.44% which were significantly higher than those of the control group (SPI) under the same pH (<i>P</i><0.05). The catechin-SPI complex structure could be changed under different pH treatments. Thus, soybean protein food base with good emulsibility could be prepared by regulating the pH value.(以大豆分离蛋白(soy protein isolate,SPI)为原料,制备不同pH值荷载儿茶素的蛋白复合物,利用差示扫描量热法、紫外可见光谱、荧光光谱、圆二色光谱等技术探究儿茶素和SPI相互作用机理,解析蛋白复合物热稳定性、荧光淬灭类型、结合位点数、热力学参数和二级结构含量等信息,分析儿茶素和SPI间结合亲和力以及复合物的乳化性。结果表明:不同pH值处理的儿茶素对SPI荧光淬灭方式均为静态淬灭,当pH值为3.5、5.5、6.5时,二者间相互作用力主要为静电作用力,pH值为4.5时主要为氢键和范德华力,pH值为7.0、7.5、8.5、9.5时主要为疏水相互作用。随着pH值增加,复合物的热稳定性逐渐增加,且在pH值为9.5时,SPI变性温度升高至157.09℃。当pH值为7.5时,复合物乳化活性和乳化稳定性比相同pH值下对照组(SPI组)分别显著提高7.70%和13.44%(<i>P</i>＜0.05)。不同pH值处理会改变儿茶素-S