Starch digestibility and molecular weight distribution of proteins in rice grains subjected to heat-moisture treatment

- Heat-moisture treatment in paddy rice alter the physicochemical properties of the grains.
- The hydrothermal modification makes the protein network more rigid and resistant.
- Heat-moisture treatment reduces the starch digestibility of rice grains.
- The effect of heat-moisture treatment on the resistant starch varies in function evaluation method.

The objective of this study was to evaluate the effects of the heat-moisture treatment (HMT) applied to paddy rice grains on the physicochemical properties, in vitro starch digestibility, and molecular weight distribution of proteins in rice flour. The paddy rice grains were adjusted to 13%, 16%, and 18% moisture and autoclaved at 121 °C for 30 and 60 min. The HMT promoted a reduction of the amylose content, the swelling power, and the solubility of the rice flour. Changes in the relative crystallinity and molecular weight of the proteins extracted with a sodium phosphate buffer containing 2.0% sodium dodecyl sulfate (SDDS) were observed in HMT samples. The different methods for the quantification of resistant starch resulted in distinct resistant starch contents. The HMT (18%-60 min) promoted an increase in resistant starch content and the HMT (16%-60 min) caused an increase in the slowly digestible starch in the rice flour.