单宁酸能使食物中的蛋白质变成不易消化的凝固物质，影响人体对蛋白质的吸收利用，为了阐明二者之间的作用方式，实验利用差热-热重分析、傅里叶红外光谱和荧光光谱研究了单宁酸（Tannic acid, T）对酪蛋白酸钠（Sodium Caseinate, SC）结构的影响。红外光谱表明，酪蛋白酸钠和单宁酸相互作用后，其二级结构发生了改变，β-折叠和β-转角含量相应地减少，α-螺旋、无规则卷曲结构增多；荧光光谱说明，T的加入可以使SC的荧光发生静态猝灭，由荧光强度变化速率和单宁酸的浓度的双对数回归曲线得出了T和SC的结合常数KΛ=1.30×103 L/mol，结合位点数n=1.20；热重和差热分析表明，单宁酸-酪蛋白酸钠复合物（T-SC）的玻璃化温度升高了20 ℃，变性温度升高了86 ℃。分析实验结果：单宁酸的存在使酪蛋白酸钠分子链之间的作用力增大，链段移动受阻，形成更大的立体网状结构,稳定性增加。

The digestion and absorption of protein by the human body can be affected by a solidified material formed through the interaction between tannic acid (TA) and sodium caseinate (SC) in food. In order to clarify this interaction, the effects of TA on SC were investigated by thermogravimetry/differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FT-IR), and fluorescence spectrophotometry. The results showed that TA has an important effect on the structure of SC. FT-IR demonstrated that the secondary structure of SC was modified in the presence of TA. The contents of β-sheets and β-turns decreased, while those of α-helices and random coil structures increased. Fluorescence spectra also confirmed that there was static quenching of SC fluorescence. The double logarithmic regression curve plotted using the fluorescence intensity rate of change and the TA concentration was used to obtain the binding constant and the number of binding sites, which were 1.30×103 L/mol and 1.20, respectively. TG-DTA showed that the temperatures of glass transition and thermal denaturation of TA-SC increased by 20 ℃ and 86 ℃, respectively. Analysis of the experimental results showed that the presence of TA enhanced the force between SC molecular chains, which impeded the movement of the chains and formed a larger three-dimensional network structure, thereby increasing stability.

国家自然科学基金项目（51174144）