热处理对大豆11S球蛋白溶解性和二级结构的影响

采用差示扫描量热仪、Lowry法以及傅里叶变换红外光谱法分别对大豆11S球蛋白的热性质、溶解性和二级结构进行测定与分析,研究热处理对11S球蛋白溶解性和二级结构的影响。热处理能够使大豆11S球蛋白Td和ΔH降低,导致蛋白质发生部分或完全变性。80℃热处理使大豆11S球蛋白的溶解性降低,这可能由于热处理改变了蛋白质的空间结构和表面电荷所致,此时蛋白质的α-螺旋结构逐渐转变为β-折叠和无规卷曲结构。而90℃和100℃热处理一定时间后,蛋白质溶解性又稍有升高,这可能是形成可溶性聚集体造成的。此时蛋白质的α-螺旋和β-折叠结构向β-转角和无规卷曲结构转变,表明β-转角和无规卷曲结构对热聚集体的形成具有重要作用。此外,蛋白质变性和氢键断裂是导致二级结构相互转变的重要因素。

Effect of Heat Treatment on Solubility and Secondary Structure of Soybean 11S Glycinin

The thermal properties, solubility and secondary structure of soybean 11S glycinin were measured by using differential scanning calorimetry, the Lowry method and Fourier transform infrared (FTIR) spectroscopy, respectively. The effects of heat treatment on the solubility and secondary structure of 11S glycinin were evaluated. The results obtained showed that Td and ΔH were reduced by heat treatment, leading to partial or complete denaturation of protein. Heat treatment at 80 ℃ could reduce the solubility of soybean 11S globulin, which may be due to the changes in the spatial structure and surface charge of protein caused by heat treatment. At the same time, the α-helix structure of protein was gradually transformed into β-sheet and random coil structure. However, the solubility of protein was slightly increased after heating for a certain time at 90 or 100 ℃, which was ascribed to the formation of soluble aggregates. Furthermore, the α-helix and β-sheet structures of protein were transformed into β-turn and random coil structure, indicating that the β-turn and random coil structures play an important role in the formation of heat-induced aggregates. In addition, protein denaturation and rupture of hydrogen bond were important causes for mutual transformation of the secondary structures.