Hydrocolloid‐Assisted Hydrothermal Modification of Intact Rice Kernels for Reduced Digestibility and Cooked‐Rice Quality

Cooked rice is a high‐glycemic‐index staple, and reducing its starch digestibility is therefore important. This study evaluated hydrocolloid‐assisted hydrothermal treatment of intact kernels for lowering cooked‐rice starch digestibility while preserving texture and appearance. The kernels were mildly heated near the starch onset gelatinization temperature with κ‐carrageenan, locust bean gum, xanthan gum, or guar gum (GG), each at 0.3%, then dried under humidity‐controlled conditions (50°C, 80% relative humidity). GG was further examined at 0.1%–0.5%. Hydrothermal treatment alone lowered the estimated glycemic index (eGI) from 91.3 to 86.4 without significantly changing hardness, although adhesiveness increased. Adding a hydrocolloid during mild heating altered digestibility and texture: xanthan gum lowered eGI but deformed the kernels and raised hardness and adhesiveness, whereas GG gave the lowest eGI, raised adhesiveness but not hardness, and better‐preserved kernel integrity. Increasing the hydrocolloid concentration reduced digestibility: at 0.3%, GG lowered eGI to 80.8. Raising it to 0.5%, however, lowered eGI only slightly further (to 79.2) while markedly increasing adhesiveness and causing kernel agglomeration. Thus, 0.3% GG most effectively reduced digestibility while preserving cooked‐rice quality. Differential scanning calorimetry indicated that the reduced digestibility did not arise primarily from internal starch reorganization: the thermal profile of the treated kernels became more native‐like even as digestibility fell. It was therefore more likely associated with a GG‐rich surface layer that restricted kernel swelling. Overall, hydrothermal treatment with 0.3% GG is a simple, commercially viable strategy for lowering the starch digestibility of cooked rice while retaining texture and appearance comparable to native rice.