Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2011
Publication Date: 11/12/2012
Citation: Luthria, D.L., Liu, K., Memon, A.A. 2012. Phenolic acids and antioxidant capacity of distillers dried grains with solubles (DDGS) as compared with corn. Journal of the American Oil Chemists' Society. 89:1297-1304.
Interpretive Summary: It is well documented that diets rich in fruits, vegetables, and grains lower the risk of certain diseases relating to oxidative damage, such as coronary heart diseases, stroke, and certain forms of cancers. Such health beneficial properties have partially been attributed to the presence of phenolic phytochemicals that are ubiquitously distributed throughout the plant kingdom. Phenolic acids belong to an important subclass of the broader category of secondary metabolites commonly referred to as phenolics, accounting for the one-third of the total dietary phenols. The major phenolic compounds present in corn and other cereal grains are cinnamic acid derivatives, mainly consist of p-coumaric, caffeic, ferulic and sinapic acids, with ferulic being the most abundant. Distiller dried grains with solubles (DDGS) is a major co-product of dry grind processing of grains (mostly corn) into fuel ethanol. It is commonly used as livestock feed. Like fuel ethanol, DDGS has quickly become a global commodity in recent years. Most previous studies on DDGS have focused on proximate composition, amino acid composition, and mineral contents. However, for increasing profitability of the ethanol industry it is critical to identify other valuable constituents in DDGS. In this study, our objectives were: 1) to determine and compare the phenolic acids content, composition, and antioxidant capacity of ground corn and corresponding DDGS obtained from three commercial ethanol plants, 2) to identify if there is any difference in the above listed attributes among bioethanol processing plants, and 3) to determine if there is a link between corn and DDGS in phenolic acids content, composition, and antioxidant capacity. Information gained from the present study may be of great interest to corn processors, ethanol manufacturers, and DDGS users since phenolic acids not only have health benefits to animals but also impact on organoleptic (flavor, astringency, and hardness) properties of feed. The increase concentration of phenolic acids may also assist in improving the shelf life and stability of DDGS.
Technical Abstract: Three sets of ground corn and the corresponding distillers dried grains with solubles (DDGS) were collected from three commercial plants and analyzed for individual phenolic acids by high performance liquid chromatography coupled with diode array and/or mass spectrometry and for antioxidant capacity by ferric reducing antioxidant power (FRAP) assay. The five phenolic acids identified in DDGS were vanillic, caffeic, p-coumaric, ferulic, and sinapic acids. Ferulic and p-coumaric acids accounted for about 80% of the total identified and quantified phenolic acids. In relative percent, the phenolic acids profile of DDGS was comparable to that of corn. However, in term of concentration per gram basis, total phenolic acids in DDGS was 3.40 fold higher than that of corn, while antioxidant capacity of DDGS was 2.58 fold increase over corn. These observations suggest that there was little degradation in individual phenolic acids content during dry grind processing. Furthermore, significant variation in measured in individual and total phenolic acids, and antioxidant capacity among plants existed for both corn and DDGS. The good correlations between DDGS and corn in contents of caffeic, ferulic, sinapic acids, and total phenolics, as well as antioxidant capacity indicates a strong influence of corn on DDGS phenolic acid profiles. Results from this study will be valuable to bioethanol manufacturers and feed industry.