Abstract: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.
