Chemometric Characterization of Whole Stillage and Distillers Dried Grains with Solubles from Industrial Bioethanol Production Reveals the Impacts of Processing on Fermentation Metabolites

Distillers dried grains with solubles (DDGS) is a major coproduct in corn-based bioethanol plants. As a staple feed ingredient for livestock and poultry, the nutrient profile of DDGS has been extensively documented. However, its fermentation metabolites and their association with pre- and postfermentation processing have not been well-defined. In the current study, paired whole stillage (WS) and DDGS samples from 10 biofuel plants in the eight Midwestern states of the United States were analyzed for their nutritional composition, and their fermentation metabolites were quantitatively determined by liquid chromatography-mass spectrometry analysis and then modeled by multivariate analysis. The protein, lipid, fiber, and ash concentrations of these industrial WS and DDGS samples were within the expected ranges of values. Glycerol and 2,3-butanediol were the most abundant alcohols besides ethanol, while lactic and acetic acids were the most abundant organic acids. Many alcohols, organic acids, aldehydes, ketones, and polyamines were present as minor components in highly variable concentrations. Interestingly, both WS and DDGS samples were clustered in their respective multivariate models based on two prefermentation processing platforms using different amounts of enzymes and heat, and this processing-related separation was mainly driven by the differences in multiple essential amino acids. In addition, the differences between WS and DDGS through correlation analysis showed the influences of postfermentation procedures on many organic coproducts. Overall, these results on the metabolic impacts of industrial fermentation and its pre- and postfermentation processing could be used as reference values for future development of processing and fermentation technology for bioethanol, DDGS, and valuable coproducts.