该研究以茶多酚-牛奶蛋白复合物为原料,通过测定其结合度、浊度、蛋白质二、三级结构及游离巯基含量等分析茶多酚对蛋白质结构变化的影响。结果表明,温度<65 ℃时,蛋白质浊度随茶多酚添加量的增加而降低;65 ℃时,二者的结合程度较高,游离巯基含量从17.61 μmol/g增加至19.11 μmol/g;95 ℃时,蛋白质游离巯基含量随茶多酚添加量的增加从19.89 μmol/g降低至16.58 μmol/g,浊度有所增加。经过3种不同的温度处理后,蛋白质二、三级结构变化趋势相似,以65 ℃为例,二级结构中β-转角含量随茶多酚添加量的增加从23.13%增加至32.87%,无规卷曲从9.36%增加至20.31%,而α-螺旋从49.15%降低至25.86%;此外,蛋白质内源荧光和外源荧光强度均随茶多酚添加量增加而降低,表面疏水性减小。不同温度处理下,茶多酚对牛奶蛋白结构的影响不同,这将为富含茶多酚乳制品的开发提供理论基础。
The tea polyphenol-milk protein complex was used as raw material, the effect of tea polyphenols on the structure of protein was analysed by measuring the degree of binding, turbidity, protein secondary and tertiary structure and free sulfhydryl content. The results showed that the protein turbidity decreased with the increase of tea polyphenol concentration when the temperature was less than 65 ℃. At 65 ℃, the degree of binding was higher, and the free sulfhydryl content increased from 17.61 μmol/g to 19.11 μmol/g. Moreover, at 95 ℃, the free thiol content of protein decreased from 19.89 μmol/g to 16.58 μmol/g with the increase of the tea polyphenol concentration. Meanwhile, the turbidity increased. Under the three temperature treatments, protein secondary and tertiary structure changed in a similar trend. Taking 65 ℃ as an example, the β-turn content in the secondary structure increased from 23.13% to 32.87% with the increase of tea polyphenol concentration. While the random curl increased from 9.36% to 20.31% and the α-helix decreased from 49.15% to 25.86%. In addition, both the endogenous fluorescence and the exogenous fluorescence intensity of the protein decreased with the increase of tea polyphenol concentration. At the same time the surface hydrophobicity decreased. The effect of tea polyphenols on the structure of milk protein is different under different temperature treatments. These results provide a theoretical basis for the development of tea polyphenols.
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