Effect of green tea polyphenols on the gelatinization and retrogradation of rice starches with different amylose contents

Abstract

The effect of green tea polyphenols (GTP) on the property of rice starch was investigated. 0, 5, 10 and 15% of GTP (based on rice starch weight) was added to rice starches with high (HAC), intermediate (IAC) and low (LAC) amylose contents, respectively. The gelatinization and retrogradation properties of rice starches with different amylose content containing different levels of GTP were analyzed by differential scanning calorimetry (DSC). The results exhibited that GTP could retard retrogradation of the three rice starches, which was further proved by X-ray diffraction investigation. In the DSC analysis, the temperature and enthalpy of starches gelatinization decreased with the concentration of GTP increasing. After storage at 4°C for 20 days, retrogradation enthalpy (ΔHret) for all rice starches with different levels GTP began to appear, and the ΔHret and degree of retrogradation (DR%) of the three rice starches significantly decreased with the increased level of GTP. The X-ray diffractogram indicate that all the three gelatinized rice starch gels showed B-type X-ray diffraction patterns, and the B-type X-ray diffraction patterns gradually disappeared with the concentration of GTP increasing. Key words: Green tea polyphenols, rice starch, gelatinization, retrogradation, differential scanning calorimetry, X-ray diffraction.