This study examined the effect of heat–moisture treatment (HMT) at 100, 110, or 120 °C for 10 min on the multi-scale structure, functional properties, and in vitro digestibility of the starch isolated from low-GI rice. The HMT decreased the leaching rate and swelling power of the starch, compared to those of the untreated starch. The relative crystallinity decreased, and the short-range molecular order increased as the treatment temperature increased from 24.3% to 15.8%. The weight-average molecular weight decreased from 1.7 × 107 g/mol to 0.9 × 107 g/mol with a broad molecular weight distribution and increased particle size. The proportion of the short amylopectin chains (DP 6–12) increased while that of the long chains (DP > 36) decreased. Mild HMT (100 °C) increased gel strength, while higher-intensity HMT (110–120 °C) reduced G′ as measured by rheology. The content of rapidly digestible starch in rice starch was reduced from 68.7% to 57.4%, slowly digestible starch was increased from 24.5% to 26.8%, resistant starch was enhanced from 6.9% to 15.8%, and the digestion lag time was prolonged to 28.62 min. The in vitro digestion assays indicated that the estimated glycemic index of starch treated at 120 °C was 48.80. This sample exhibited the highest suppression of digestibility. It also showed the highest increase in resistant starch content. The results provide a theoretical ground for low-GI product development from HMT modified rice starch.
Zhou et al. (Tue,) studied this question.