以大豆蛋白(soy protein isolate, SPI)和油茶籽蛋白(camellia seed protein isolate, CPI)为原料制备热诱导混合凝胶,测定了混合物凝胶的流变性质、质构、持水性和凝胶结构,并基于2种蛋白各自的氨基酸组成、混合物溶解度、电泳、表面自由巯基、二硫键、表面疏水性、溶液粒径分布、二级结构等探索混合物凝胶增强的机制。结果表明,当SPI与CPI的复配比例为10:2~10:3时,复配蛋白的凝胶点温度由82.34 ℃降低至75.73 ℃,储能模量值达到最大,是纯SPI的5倍;凝胶强度达到最大,是纯SPI的2倍。电镜结果显示,适当比例的CPI能够使复配蛋白形成致密均匀的凝胶网络结构。电泳、表面自由巯基和二硫键结果显示,2种蛋白间发生二硫键参与的相互作用并形成了复合物,这种相互作用能降低复合物表面疏水性,有效提高SPI溶解度,促使凝胶网络结构更加致密均匀。红外光谱结果显示,复配蛋白的二级结构由β-折叠向β-转角和无规则卷曲转变。上述结果说明一定比例的油茶籽蛋白对SPI凝胶强度具有提升作用,该研究为将来制备高凝胶植物基混合蛋白提供了新的思路和理论依据。
Heat-induced mixed gels were prepared with soybean protein isolate (SPI) and camellia seed protein (CPI) as raw materials. The rheological properties, texture, water holding capacity, and gel structure of the mixed gels were determined. The interaction between the two proteins and the mechanism that lead to the improvement of the mixture gel were explored based on the respective amino acid compositions of the two proteins, the solubility, electrophoresis, surface free sulfhydryl groups, disulfide bonds, surface hydrophobicity, solution particle size distribution, secondary structure, gel microstructure, etc. Results showed that when the compounding ratio of SPI and CPI was between 10:2 and 10:3, the gelling point temperature of the mixed protein decreased from 82.34 ℃ to 75.73 ℃, and the storage modulus value reached the maximum, which was 5 times that of pure SPI. Meanwhile, the gel strength reached the maximum, which was 2 times that of pure SPI. Moreover, the electron microscopy results showed that an appropriate proportion of CPI enabled the mixed protein to form a dense and uniform gel network structure. The results of electrophoresis, surface free sulfhydryl content, and disulfide bonds content showed that the two proteins interacted by disulfide bonds and was formed a complex between the subunits, which could reduce the surface hydrophobicity of the complex and effectively improve the solubility of SPI, it also could promote the gel network structure to be denser and more uniform. Furthermore, infrared spectroscopy results showed that the secondary structure of the mixed protein was changed from β-sheet to β-turn and random coil. Above results indicated that the improvement of the gel strength of soy protein by a certain proportion of camellia seed protein was mainly based on the interaction between the two proteins. A certain proportion of camellia seed protein had an enhancement effect on the gel strength of soybean protein, which provided a new thought and theoretical basis for the preparation of high gel plant-based mixed protein in the future.
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