Investigation of changes in the fine structure of sorghum starch in the baijiu fermentation process

In fermentation to produce the alcoholic liquor baijiu, sorghum starch is the main carbohydrate source, being hydrolyzed and converted into ethanol and aromatics. The mechanisms of starch hydrolysis which affect fermentation quality and efficiency are not fully understood. To investigate this, three sorghum varieties were used as fermentation material, with two fermentation methods. Changes in the amounts of various components and in starch molecular structure in lees (sediment) during fermentation were investigated. The lees from waxy sorghum had higher fermentation rates and saccharification power than those from normal sorghum in the early stage of fermentation, but decreased below those of normal sorghum in the end stage of fermentation, due to increased accumulation of acid, which inhibited enzyme activities, and even stopped fermentation. The chain-length distributions of both amylopectin and amylose in the lees did not show significant changes with fermentation, showing that starch in sorghum grain cannot be hydrolyzed directly, but only by hydrolysis of starch leached from the grain into the water; this is in accord with data from electron micrographs indicating that starch hydrolysis happened in the leachate rather than in the lees. This information can help manufacturers fine-tune their processes to improve production processes and product. [Display omitted] •Starch molecular structure affects the process and final product of the liquor baijiu.•Components, acidity and enzyme-mixture activity changes during fermentation were measured.•Higher amylopectin content first increased fermentation rate, and then decreased it.•Starch fine structure showed starch was insignificantly hydrolyzed in fermentation.•The brewing method affected acid resistance, starch usage and fermentation rates.