A simple innovation, soaking raw rough rice in warm water at 65°C before de-husking, can significantly improve the health-related properties of rice without changing the rice type or eating habits. The study found that treated rice had lower starch digestibility, with maximum hydrolysis reduced from about 97% to 87–90%. This indicates a slower glucose release, which may help better control blood sugar levels. 

The soaking duration also affects texture, as longer soaking results in firmer and more adhesive cooked rice. Although a slight yellowish color may develop, the overall quality remains comparable. This technology shows strong potential for developing health-oriented foods by reducing the proportion of digestible starch, thereby adding value and meeting the needs of modern health-conscious consumers.

Topic: Effect of warm water soaking for raw rough rice on in vitro starch digestibility of cooked rice

Authors: Thuengtung, S.| Ding, Y.| Ketnawa, S.| Cai, Y.| Wang, L.| Ogawa, Y.

Abstract: 

BACKGROUND

The present study investigated the influence of mild heat treatment on harvested raw rough rice (Oryza sativa L. cv. Toyomeki) by warm water soaking at 65 °C with respect to the physicochemical properties and starch digestibility of cooked rice. Changes in color, texture, starch attributes and simulated in vitro digestibility were examined.

RESULTS

The results indicated that the b* value increased with a soaking duration, but the treated rice showed little change in the whiteness index value compared to untreated rice. No significant differences were also observed in the resistant starch content and kinetic constant. A positive correlation was found between firmness and adhesiveness of the cooked (P < 0.01). However, the treated rice showed a lower equilibrium level of starch hydrolysis than untreated rice.

CONCLUSION

The application of mild heat soaking treatment for raw rough rice could be considered an effective technique to control the potential health-related properties of cooked rice. 

Source: Journal of the Science of Food and Agriculture Volume 106 (1) (January 2026)

Keywords: warm water soaking; raw rough rice; physical property; resistant starch

View at publisher: https://scijournals.onlinelibrary.wiley.com/doi/10.1002/jsfa.70167