Physicochemical characteristics of waxy rice starch influencing the in vitro digestibility of a starch gel

Starches were isolated from three waxy rice varieties: Koganemochi (Kog), Hakuchomochi (Hak), and Kantomochi 172 (K172). Forty percent starch gels were prepared and the extent of starch gel digestibility was determined by an in vitro method. The distribution of chain lengths of amylopectin was analyzed and differential scanning calorimetry was used to analyze gelatinization and retrogradation of waxy rice starch. The K172 gel had significantly higher resistance to hydrolysis than had the other gels. The K172 starch contained lower proportions of the short chains of amylopectin and showed higher gelatinization temperature and enthalpy. The retrogradation peak was measured using waxy rice starch gels stored for 1 and 7 days at 5 °C. The K172 gel was observed to retrograde more quickly and to have a greater extent of retrogradation than the other gels. The difference in amylopectin chain length distribution and recrystallinity contributed to the variation in the starch gel digestibility of waxy rice.