Mechanistic investigation of impact of malic acid, ultrasound and dual treatment on starch digestibility of cooked whole rice grains

Physical, chemical, and dual modifications can all significantly affect the digestibility of isolated rice granules, while their effects on the starch digestibility of whole cooked rice grains remain elusive. Therefore, the impact of malic acid, ultrasound, and ultrasound + malic acid dual treatment on the starch digestibility of cooked rice grains with different starch molecular structures was investigated in this study. Ultrasound mainly caused cavitation on the surface of rice grains, promoting the leaching of materials (> 11 %) and amylose during cooking. This led to a faster retrogradation rate, smaller pores, and a lower maximum starch digestion extent. In contrast, malic acid caused a faster digestion rate due to the significant degradation of starch molecules, although its moderate esterification smoothed the cooked rice grain surface and slightly reduced the maximum starch digestion extent. Compared to malic acid treatment, the dual treatment showed a much higher degree of esterification, which may thus contribute to its significantly lower maximum starch digestion extent (up to 21 %). Collectively, these findings suggest that both ultrasound and dual treatment can be effective strategies for producing cooked rice grains with slower starch digestibility, with implications for improving the public health.