Review: protein value of distillers dried grains with solubles (DDGS) in animal nutrition as affected by the ethanol production process

Distillers dried grains with solubles (DDGS), a by-product of ethanol production from cereal grains, are used as a protein source for production animals. Like crude protein (CP) content, degradability and digestibility of CP and amino acids (AA) are predetermined by the raw material grain, but also affected by the production process to a considerable degree. This review highlights steps of the production process potentially affecting the protein value of DDGS. Heat influence during drying of DDGS is most discussed. During heating, AA can undergo a series of chemical reactions resulting in reduced digestibility or destruction of AA. To evaluate the heat influence on DDGS protein quality, measuring colour variables, acid detergent insoluble N and AA content have been applied, although all of these methods have some limitations. Besides drying, further processing steps potentially affecting the protein value of DDGS are high temperature application prior to drying or blending of product streams. Yeast protein contributes to DDGS protein but estimations of the actual amount differ considerably. Although the outlined effects and their underlying principles are known, their systematic investigation is impeded by the complex nature of the production process.