Starch Eluted from Polished Rice during Soaking in Hot Water is Related to the Eating Quality of Cooked Rice

In this study, we analyzed the starch and free sugars eluted from polished rice soaked in hot water to determine if they are correlated with the eating quality of cooked rice. Two grams of polished rice was heated with 40 mL of water at 85oC. Eluted starch varied widely among used cultivars and the amount of eluted starch was significantly correlated with overall eating quality in two years (r=0.62**, 0.77**). The amylose ratio of eluted starch, measured with high-performance size-exclusion chromatography (HPSEC), was significantly negatively correlated with overall eating quality (r=−0.84**). This fact showed that eating quality rose as the ratio of amylopectin in eluted starch increased. Although the differences in chain-length distribution of amylopectin and free sugar contents in eluted starch did not correspond to differences in eating quality, it was suggested that eating quality improved if the short–chain ratio of amylopectin in eluted starch rose. Eluted starch of rice can be analyzed using only 2 g of polished rice and does not require any special equipment. Thus, this method can be applied to the selection of high-quality rice lines in the early generations of a breeding population.