Revealing the reasons for the pasting property changes of rice during aging from the perspective of starch granule disaggregation.

BACKGROUND: The pasting properties of rice change markedly after aging, although the mechanism for this still remains unknown. Aged and fresh rice grains were ground and the flours were fractionated by particle size, and then the pasting properties, particle size distribution and microscopic morphology of the heated flour fractions were evaluated. RESULTS: Compared to the corresponding fresh flour fractions with the same particle size, a lower peak viscosity for those aged flour fractions from 80 µm to 450 µm and a higher peak viscosity for those aged flour fractions from 20 µm to 60 µm were observed. The amounts of smaller particles disaggregated from the aged flour fractions were significantly less and the separated entities were always larger than the corresponding fresh rice fractions. CONCLUSION: Disaggregation difficulty of starch granules was the reason for the changes in the pasting properties of rice after aging. This finding is helpful for understanding rice aging mechanisms and regulating eating quality of rice flour as an ingredient. © 2022 Society of Chemical Industry.

Restoring fresh texture in cooked aged rice with reducing agents.

Effects of ascorbic acid and sodium sulfite on texture of cooked aged rice were researched in this study. Hardness increase and stickiness reduction are common for cooked aged rice. The texture of cooked aged rice was significantly changed approaching to fresh rice by both reducing agents despite of sulfur-containing or not (p < 0.05), and the values of hardness, stickiness and stickiness/hardness ratio could be completely restored to the levels of the corresponding fresh rice. Moreover, this effect showed a dose-effect relationship. Morphology examination suggested that ascorbic acid made starch granules swelling adequately and full of larger dents in the interior of cooked aged rice, while sodium sulfite only made starch granules displayed relatively smaller dents. Particle size analysis indicated that ascorbic acid enhanced the swelling and separation of starch granules, but sodium sulfite only promoted the granule separation due to deagglomeration. Therefore, the two reducing agents are useful in restoring texture of aged rice to fresh rice through changing gelatinization behavior and can be as a key probe to disclose aging mechanisms of rice.