Effect of Particle Size and Roasting Conditions on the Quality of High-Resistant Starch Rice

This study investigated the effects of roasting temperature (130 °C, 150 °C, 180 °C) and grinding fineness (10, 50, and 100 mesh) on the nutritional quality and physicochemical properties of high-resistant starch rice flour (Youtangdao 3). The results revealed that the process of whole-grain moist roasting, followed by milling and sieving, markedly enhanced the resistant starch (RS) content while concurrently reducing the fraction of rapidly digestible starch (RDS). Specifically, roasting at 130 °C with coarse grinding (R130-10) yielded the highest absolute RS content (27.45 g/100 g). However, for fine-particle fractions essential for food texture, roasting at 150 °C (R150-100) proved optimal by achieving the highest RS proportion within the starch matrix (89.36% by Englyst method). Structural analysis via X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that roasting facilitated the reorganization of starch chains. This molecular rearrangement led to a pronounced increase in crystallinity and induced distinct morphological alterations within the granules. Furthermore, Rapid Visco Analyzer (RVA) profiling indicated a substantial decline in peak viscosity for all roasted samples, indicating a significant loss of pasting ability and an increase in structural rigidity. In conclusion, the combination of moderate roasting temperature and precise particle size control effectively optimizes the nutritional value of high-RS rice flour. These insights provide a theoretical basis for developing high-RS rice flour ingredients.