Investigation on the multi-scale structure and digestibility of starch in sweet rice wine and its vinasse: Insights from indica and glutinous rice varieties

Sweet rice wine is a traditional Chinese fermented beverage in which starch serves as the primary fermentation substrate. After sweet rice wine fermentation, low-molecular-weight starch remained in the fermentation mash (IRWS, indica sweet rice wine starch: 390.7 kDa; GRWS, glutinous sweet rice wine starch: 606.3 kDa), whereas higher-molecular-weight starch concentrated in the vinasse (IRVS, indica rice vinasse starch: 6954.9 kDa; GRVS, glutinous rice vinasse starch: 77,499.6 kDa). Compared with cooked rice starch, vinasse starches showed reduced digestibility, with resistant starch contents of IRVS and GRVS increasing from 25.48 % and 16.15 % to 30.88 % and 23.36 %, respectively. Structurally, GRVS retained a branched architecture similar to its native counterpart, whereas IRVS underwent significant structural changes, marked by an increase in long amylopectin branches, and a B + V-type crystallization formed based on high amylose content and starch retrogradation. Small-particle starch in the fermentation mash, IRWS and GRWS, exhibited B + V-type crystallization, high short-range order, elevated peak gelatinization temperatures (IRWS: 90.5 °C; GRWS: 101.3 °C), and strong resistance to enzymatic digestion. Both contained long-linear dextrin polymers with degrees of polymerization concentrated at 200–300 (IRWS) and 300–400 (GRWS). These results provide a theoretical basis for the quality improvement of sweet rice wine and the utilization of by-products.