Effect of heat pre-treatment at different temperatures with different cooking techniques on the resistant starch, physicochemical and thermal properties of white rice

The composition of resistant starch (RS) in high glycemic index food like white rice could contribute to altering its dietary glycemic load, which would be a promising strategy in managing obesity and improving dietary fiber intake. Heat pre-treatment, cooking methods and temperatures are among the key factors to impact RS content. This study aimed to investigate the effect of pre-treatment (oven heating) at different temperatures with different cooking techniques (steaming or boiling) on RS, physicochemical and thermal properties, and crystallinity of white rice. The study demonstrated steam-cooked rice with pre-treatment at 55, 75, and 95 °C increased RS to 5.96%, 5.99%, and 5.48%, and amylose content increased to 34.18%, 37.87%, and 21.59% respectively. In contrast, rice cooked with boiling method after pre-treatment at 55, 75, and 95 °C decreased RS to 4.13%, 5.54%, and 3.66%, and amylose content decreased to 22.91%, 25.35%, and 21.55% respectively. Thermal properties and crystallinity of treated rice were analyzed via differential scanning colorimetry and X-ray diffraction (XRD). The gelatinization temperatures of all treated rice had significantly decreased because of reduced amylose content and slightly weakened starch crystalline structure. The XRD analysis revealed a V-type pattern and a slightly weak A-type pattern for all treated rice. Overall, rice treated at 75 °C followed by steam cooking performed the best in terms of amylose, RS contents, and textural properties (hardness and stickiness), hence can be suggested for obese people to improve their dietary fiber intake in their daily diet.