Effects of cooking, retrogradation and drying on starch digestibility in instant rice making

Abstract

Instant rice has become increasingly popular due to its convenience. Reducing the starch digestibility of instant rice may increase its potential health benefits. The aims of this study were to define the optimum conditions for cooking, retrogradation and drying to reduce the in vitro starch digestibility of instant rice. Three varieties of rice from Taiwan (low-amylose japonica [Taikeng 9], low-amylose indica [Taichung Sen 10] and high-amylose indica [Taichung Sen 17]) were prepared using different cooking conditions and durations of retrogradation. Starch digestibility was determined by analyzing the amount of rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) in the instant rice. Cooking at 86 °C for 28 min in a 1.0-fold volume of water significantly reduced RDS and increased SDS compared to rice cooked on a traditional electronic cooker. The combination of retrogradation and low-temperature drying significantly reduced the RDS of instant rice after rehydration. A reduction in RDS was accompanied by an increase in SDS and RS in low-amylose japonica rice, increased RS in low-amylose indica rice, and reduced SDS and increased RS in high-amylose rice. Optimizing cooking methods and retrogradation reduced the starch digestibility of instant rice; this may help improve its healthful qualities.