Morphological and physicochemical properties of two starch mutants induced from a high amylose indica rice by gamma irradiation

Abstract

AbstractMorphological and physicochemical properties of two starch mutants isolated from a high amylose indica rice, Guangluai 4 (GLA4), were characterized. One is waxy mutant (GM077) with opaque endosperm, which had low amylose content (2.6%) and had a characteristic RVA pasting viscosity curve with a rapid increase and rapid breakdown in viscosity from onset to peak viscosity and during temperature holding step, respectively. The other is white‐core mutant (GM645) with a chalky endosperm in the center of the grain. The starch granules in the chalky part are round and a little smaller than those in the other part, which had polygonal shape. GM645 had an amylose content of 22.8%. RVA pasting viscosity of GM645 flour was smaller than that of its parent GLA4, while that of its starch was higher than GLA4. The gel hardness of GM645 flour and starch was less than that of GLA4. GM077 had higher peak temperature (Tp, 79°C) than GLA4 (77°C), and the GM645 had the lowest gelatinization temperature. GLA4 had the largest retrogradation percentage (34.7% for flour and 29.7% for starch), whereas GM077 had the smallest retrogradation percentage among the three rice starches (9.6% for flour and 12.8% for starch). GM077 had more chains with DP 6–10, DP 18–33, and DP ≥44 than GLA4, and GM645 had more chains with DP 6–9, DP 22–35, and DP ≥44 than GLA4. Application of the starch mutants in food processing, and identification of defect genes for functional genomics study with these two mutants were also discussed.