Starch structural reasons for the effects of SSIIIa deficiency on the textural and digestive properties of cooked rice

Due to the urgent requirements for development of healthy diets, foods with slow digestibility combined with superior eating quality attract increasingly more attention. A high amylose indica rice mutant with starch synthase IIIa (SSIIIa) deficiency was reported to have higher resistant starch content, while how the starch structure affects the textural and digestive properties of the cooked rice have not been clarified. The ss3a starch had a significantly higher amylose content (AC), longer amylose intermediate chains but shorter amylose long chains, and also displayed a higher proportion of amylopectin A, B1, and B2 chains but a lower amount of B3 chains and shorter chain length of amylopectin molecules. The gelatinization temperatures and paste viscosity were decreased because of the increased AC and more amylopectin short chains, which further contributed to the harder texture of cooked rice. In addition, more amylose intermediate to long chains and longer amylose intermediate chains of the mutant resulted in the slow digestion rate of the fast-digestible fraction, and less amylopectin intermediate to long chains caused the complete digestion of cooked rice. These findings explained the nutritional benefits of the ss3a rice and its importance to the production of slow-digestive food products with acceptable texture.