How sorghum starch structural properties affect its resistance to cooking in baijiu brewing

Abstract

The Chinese liquor baijiu is made from fermented sorghum grain. During fermentation, the cooking resistance (starch leaching rate) is an important factor for both baijiu producers and sorghum breeders, to select and breed suitable sorghum varieties. The factors and mechanisms which affect this resistance are not well understood. To investigate this, fifteen brewing sorghum varieties were used for brewing, with sampling over cooking time. The components, starch molecular structure and particle morphology of these samples were characterized and correlated with cooking parameters. In this study, high crystallinity and gelatinization enthalpy in sorghum grains were found to reduce cooking resistance by enhancing swelling power to break the seed coat and cell wall. This is the opposite of what happens in other cereal grains. High protein content, high particle size and high amylose content are the main factors for improving cooking resistance, which occurs by the formation of a cross-linked 3D structure and reduced water absorption to inhibit gelatinization. Both the average and the distribution of chain lengths of amylopectin and amylose are important factors affecting cooking resistance because, among other things, of their influence on crystal structure. This information might help manufacturers select and breed sorghum varieties which have optimal behavior for a given brewing method.