Recommendations published on analytical test methods for distillers grains
The Renewable Fuels Association (RFA) and American Feed Industry Association (AFIA) have published recommendations on analytical test methods for the testing of corn distillers dried grains (DDG) and corn DDG with solubles (DDGS) in the JOURNAL OF AOAC INTERNATIONAL VOL. 92, NO.1, 2009.
The recommendations are based on inter-laboratory studies in which FOSS was involved, participating in the trials and supplying analytical solutions. A number of FOSS solutions are stated as recommended methods:
- Protein (Crude) in Animal Feed and Pet Food (Copper Catalyst) according to AOAC 2001.11 – FOSS Kjeltec 8000 series
- Oil in Cereal Adjuncts (Petroleum Ether) according to AOAC 945.16 - FOSS Soxtec™
- Fiber (Crude) in Animal Feed and Pet Food (F.G. Crucible) according to AOAC 978.10 – FOSS - Fibertec™
Rapid indirect solutions available
FOSS also provides rapid indirect solutions for routine analysis of the same sample types and parameters. Both the XDS Rapid Content Analyser™ and the InfraXact™ analyser can be used.
More information about FOSS and the biofuel industry can be found
Additional background information from the published article
Corn distillers dried grains (DDG) and corn DDG with solubles (DDGS) are co-products of fuel and beverage ethanol distilleries. They are the second-largest processed feed ingredient in the United States. The absence of industry guidelines and recommendations on analytical test methods for the testing of DDGS has led to a high level of confusion related to analysis and subsequent interpretation of data for moisture, protein, fat, and fiber, all of which are critical feed qualities and trade parameters.
A number of analytical methods for constituents commonly measured in distillers dried grains (DDG) are practiced in laboratories serving the agricultural sector. A large inter-laboratory 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 inter-laboratory variation of a number of methods for moisture, crude protein, crude fat, and crude fiber in DDG with solubles (DDGS).
A second study was undertaken to assess existing inter-laboratory 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.
FOSS has actively taken part in this process, partly by working in the AFIA DDGS Analytical Methods Sub-Working Group and partly by participating in the inter-laboratory trials and is supplying validated and traceable solutions for these methods.
Notable is that the most common method for moisture determinations, AOAC 930.15, Loss on Drying for Feeds (135o C/3 h), was shown to dramatically overestimate the moisture content in DDGS and, therefore, use of this method is highly discouraged. Efforts to remove the method from use on DDGS are to be pursued. Instead the NFTA method 188.8.131.52 (105 ºC / 3 h) is recommended.
The protein methods investigated were statistically equivalent and can be used interchangeably to provide accurate and precise protein results on DDGS. FOSS supplies the Kjeltec line of instruments for the recommended AOAC 2001.11 method.
For crude fat the AOAC method 945.16, Oil in Cereal Adjuncts, using Petroleum Ether as solvent is recommended as it has proven to be the most robust method. Interesting to note that acid hydrolysis method for total fat is resulting in almost 150% of the value of the direct extraction method. Further study is suggested to determine whether the acid hydrolysis step is needed to free all lipid material from the DDGS matrix. Both direct extraction and acid hydrolysis methods are easily performed using the FOSS Soxtec solution.
For crude fibre the AOAC method 978.20, Fiber (Crude) in Animal Feed and Pet Food (crucible method) is the recommended. This method is run on the well known FOSS Fibertec systems. The alternative filter bag method with commercially available filter bags was shown to cause a 10% (relative) low bias.
NANCY THIEX, Evaluation of Analytical Methods for the Determination of Moisture, Crude Protein, Crude Fat, and Crude Fiber in Distillers, JOURNAL OF AOAC INTERNATIONAL VOL. 92, NO. 1, 2009, 61-73
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