Physicochemical evolution of sorghum grain starch under the condition of solid-state fermentation of Baijiu

Glutinous sorghum grains were fermented for varying durations (1, 2, 3, 5, 8 and 12 w) to investigate the effects of fermentation on the starch within the grains. Starch conversion rate and Baijiu yield continued to increase in the first 8 w of fermentation, peaking at 63.7 % and 45.7 %, respectively. The increasing rate was about eight times the subsequent decline rate. Images of CLSM revealed that the swollen starch granules progressively vanished during fermentation, transforming into irregular fragments. The total starch content decreased by 69.0 %, and almost only amylopectin remained in the grains at 12 w. The utilization rate of amylose (98.3 %) was higher than that of amylopectin (66.2 %), and the higher the amylose content, the faster the production of Baijiu. Additionally, fermentation reduced high-molecular-weight components and increased low-molecular-weight ones. The weight average molecular weight (Mw) of starch in the grains dropped from 9.13×10⁷ g/mol to 8.02×10⁵ g/mol. The considerable decline in starch content and molecular weight led to a substantial decrease in the final viscosity of sorghum flour, from 392 cP to below 10 cP. The findings provide a theoretical basis for intelligent control of multi-round fermentation in the Baijiu brewing industry.