DisplayTitle

Methods for Characterization of Residual Starch in Distiller's Dried Grains with Solubles (DDGS)

¹Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011. ²Current address: Nestlé Research Center, Department of Food Science and Technology, PO Box 44, Vers-chez-les-Blanc, CH-1026 Lausanne, Switzerland. ³Corresponding author. Phone: 1-515-294-9892; Fax: 1-515-294-8181 E-mail: jjane@iastate.edu

The objective of this study was to establish methods for determining the content and components of residual starch in distiller's dried grains with solubles (DDGS), a coproduct from dry-grind corn ethanol production. Four DDGS prepared in our laboratory and one DDGS obtained from a commercial ethanol manufacturer were used for the study. Quantitative analysis of total residual sugar (TRS) in DDGS was performed by determining D-glucose produced by enzymatic hydrolysis of oligosaccharides and residual starch remaining in hexane-defatted DDGS after being dispersed in 90% DMSO. The TRS consisted of free glucose, oligosaccharides, and residual starch. The commercial manufacturer's DDGS contained more TRS (15.8%, w/w db) than the laboratory-processed DDGS (2.4–2.9%, w/w db). The content of residual starch remaining in the commercial DDGS (5.5% w/w db) was also larger than the laboratory-processed DDGS (1.9–2.5% w/w db). Analyses of molecular weight distribution showed that the residual starch in DDGS consisted of short-chain amylose and amylopectin, respectively, as the major and minor components. The short-chain amylose molecules constituted 86.5–94.1% of the residual starch. The major population of the short-chain amyloses had an average degree of polymerization (DP) of 85, closely resembling the length of enzyme-resistant fragments of amylose-lipid complexes.