Chemical Composition of Distillers Grains, a Review

Abstract

In recent years, increasing demand for ethanol as a fuel additive and decreasing dependency on fossil fuels have resulted in a dramatic increase in the amount of grains used for ethanol production. Dry-grind is the major process, resulting in distillers dried grains with solubles (DDGS) as a major coproduct. Like fuel ethanol, DDGS has quickly become a global commodity. However, high compositional variation has been the main problem hindering its use as a feed ingredient. This review provides updated information on the chemical composition of distillers grains in terms of nutrient levels, changes during dry-grind processing, and causes for large variation. The occurrence in grain feedstock and the fate of mycotoxins during processing are also covered. During processing, starch is converted to glucose and then to ethanol and carbon dioxide. Most other components are relatively unchanged but concentrated in DDGS about 3-fold over the original feedstock. Mycotoxins, if present in the original feedstock, are also concentrated. Higher fold of increases in S, Na, and Ca are mostly due to exogenous addition during processing, whereas unusual changes in inorganic phosphorus (P) and phytate P indicate phytate hydrolysis by yeast phytase. Fermentation causes major changes, but other processing steps are also responsible. The causes for varying DDGS composition are multiple, including differences in feedstock species and composition, process methods and parameters, the amount of condensed solubles added to distiller wet grains, the effect of fermentation yeast, and analytical methodology. Most of them can be attributed to the complexity of the dry-grind process itself. It is hoped that information provided in this review will improve the understanding of the dry-grind process and aid in the development of strategies to control the compositional variation in DDGS.

Spectroscopic impact on protein and carbohydrate inherent molecular structures of barley, oat and corn combined with wheat DDGS

“…However, high content of lignin (ADL, 43 g/kg) reported by Nuez-Ortin and Yu [17] may lead its nutritional value low. Although it contains high protein, fat and fibre and low starch [12], DDGS were reported to be slow in degradability and digestibility in rumen because ready available fermentable fractions were already grain). All samples were in replicate and undergone molecular spectral analyses.…”

Novel coproducts from corn milling and their use in ruminants’ nutrition

“…Although the technological processes are more and more controlled, processors pay more attention to the production efficiency and quality of the main products and sometimes neglect the quality of the coproducts. Thus, poor control of the drying conditions may lead to a decreased digestibility of protein and fibre (19,43), high occurrence of mycotoxins (17,53,54), or high differences in quality among batches and producers (17). More research is needed on this subject in order to assess the incidence of these quality problems and to develop specific tools for prevention or mitigation.…”

“…Although the two new coproducts are expected to have low variability in their chemical composition (19), there are still some variations, e.g., in neutral detergent fibre (NDF) or acid detergent fibre (ADF). Beside the possible influences of the applied analytical methods, this variability may be determined by the variation in raw materials traits, content of residual fat, and processing conditions (17,20,21). This maintains the need for their periodical analysis, similarly to regular DG, especially when changing the provider (11).…”

“…The authors highlighted, however, that lysine is the first limiting amino acid, as also shown by other studies (28,61), which warns about the potential lysine deficiency of HPDG, especially at high dietary proportions. Moreover, lysine is highly susceptible to heat damage (17), which makes important the influence of processing conditions and highlights the need of specific analysis when large quantities of corn coproducts are involved. When replacing a mixture of soybean meal and Soy Pass in diets of dairy cows at 20% of DMI (48), HPDG induced an increase of the milk yield and fat-corrected milk (from 31.6 to 33.4 L/day and from 33.2 to 36.3 L/day, respectively) that also induced further increase of the feeding efficiency.…”

“…Thus, in recent years, there has been a strong tendency to shift from regular DG to RFDG, using various techniques/approaches (solvents, degermination, separate valorisation of soluble fraction, etc.). Beside the regular cautions related to coproducts such as transparency of the processing technology, consistency of batches, and the need for periodical chemical analyses (17), two more issues need to be highlighted.…”