Evaluation of analytical methods for the determination of moisture, crude protein, crude fat, and crude fiber in distillers dried grains with solubles.

A number of analytical methods for constituents commonly measured in distillers dried grains (DDG) are practiced in laboratories serving the agricultural sector. A large interlaboratory variability among results has been observed in the industry. Methods for moisture, crude fat, and crude fiber are empirical, thus part of this variability can be attributed to the use of different methods of analysis. A study was organized and supported by the American Feed Industry Association, the Renewable Fuels Association, and the National Corn Grain Association to evaluate the efficacy, applicability, and the intralaboratory variation of a number of methods for moisture, crude protein, crude fat, and crude fiber in DDG with solubles (DDGS). The moisture methods included in the study are AOAC 930.15, AOAC 934.01, AOAC 935.29, AOAC 2003.06, and National Forage Testing Association (NFTA) 2.2.2.5; the crude protein methods studied are AOAC 990.03 and AOAC 2001.13; the crude fat methods studied are AOAC 945.16, AOAC 954.02, AOAC 2003.05, and AOAC 2006.06; and the crude fiber methods studied are AOAC 978.10 and AOCS Ba 6a-05. A second study was undertaken to assess existing interlaboratory variation of the same methods in 23 laboratories. Based on the results of these studies, the sponsoring associations established recommended reference methods for use in commercial trade of DDGS. The reference methods selected are NFTA 2.2.2.5 for moisture, AOAC 990.03 and AOAC 2001.11 for crude protein, AOAC 945.16 for crude fat, and AOAC 978.10 for crude fiber.