Characteristics of Tea Polyphenol and Buckwheat Starch Blending System and Structural Characterization of Their Complexes

This study focused on buckwheat starch as the research subject and investigated the effects of different addition levels of tea polyphenols (TP) (0%, 2%, 5%, 10%, and 20%) on the physicochemical properties of buckwheat starch. Differential scanning calorimetry, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used to characterize the structure of the buckwheat starch–tea polyphenol complexes. The results showed that, compared with the control group without tea polyphenols, as the TP addition increased from 0% to 20%, the peak viscosity, trough viscosity, and final viscosity decreased by 52.15%, 36.2%, and 53.0%, respectively (P<0.05). The addition of tea polyphenols contributed to improving the thermal paste stability of the starch. Both the onset gelatinization temperature and peak temperature decreased with increasing tea polyphenol addition (P<0.05), and the enthalpy of phase transition decreased from 10.1 J/g to 1.79 J/g. In terms of rheological properties, the addition of tea polyphenols significantly reduced the viscoelasticity and apparent viscosity of the starch gel. The color of the gel changed progressively from white to red and then to pink-brown with increasing concentrations of tea polyphenols. During heating, both the solubility and swelling power of starch increased with rising temperatures (P<0.05). Notably, solubility was positively correlated with tea polyphenol concentration (P<0.05), while swelling power showed a negative correlation (P<0.05). Further characterization using scanning electron microscopy Fourier-transform infrared spectroscopy, and thermogravimetric analysis revealed that the composites formed after the addition of tea polyphenols exhibited a looser network structure. The R_1047/1022 ratio initially increased and then decreased with increasing tea polyphenol content (P<0.05). Additionally, the thermal stability of the composites at high temperatures was improved. The above findings may provide theoretical guidance for the application of buckwheat starch in the food industry and lay a foundation for the further development of starch-based food products.