Title: Modification of an AOCS Official Method for Crude Oil Content in Distillers Grains Author
Submitted to: AOCS Lipid Library
Publication Type: Other
Publication Acceptance Date: June 24, 2011
Publication Date: August 1, 2011
Repository URL: http://riley.nal.usda.gov/nal_web/digi/submission.html
Citation: Liu, K. 2011. Modification of an AOCS Official Method for Crude Oil Content in Distillers Grains. AOCS Lipid Library, an on-line publication, available since 08/01/2011. http://lipidlibrary.aocs.org/topics/oilcontent-Liu/index.htm Interpretive Summary: This paper is within The Lipid Library, which is an on-line publication, sponsored by American Oil Chemists Society (see website: http://lipidlibrary.aocs.org/index.html ). It deals with information relating to lipid chemistry, biology, technology, and analysis. This article is under Lipid Analysis, selected topics in the analysis of lipids ( http://lipidlibrary.aocs.org/topics/oilcontent-Liu/index.htm ). Currently, there are a few official standard methods available for measuring crude fat/oil content in various types of feed and agricultural products. There is also an alternative to the Soxhlet type of extraction methods. It is based on filter bag technology developed by Ankom Technology Inc. (Macedon, NY). This alternative method was approved by American Oil Chemists’ Society as an Official Procedure, Am 5-04, (2005). In recent years, there is a dramatic increase in the amount of starchy grains used for ethanol production. A major process for making ethanol from corn and other grains is the dry-grind method, with distillers dried grains with solubles (DDGS) as a main co-product. Chemical composition of DDGS has been of great interest to researchers in animal science, ethanol producers, and traders in feed industry. Oil is the third most abundant component of DDGS. Accurate measurement of the oil content in DDGS is critical because it is not only a major nutrient but also a condensed energy source. In theory, any of the above methods may be suitable for measuring crude oil content in DDGS. However, a recent study was conducted at the author’s lab to compare several factors affecting crude oil analysis of DDGS by the AOCS Official Method, Am 5-04, as compared with milled corn, the feedstock for the dry-grind process. What was found in the study is that the AOCS official method Am 5-04 has to be modified in order to have accurate measurement of oil content in DDGS samples. The possible explanation for modification is that DDGS has undergone some harsh treatments (enzymatic, pH change and heat) during dry-grind processing of grain into fuel ethanol and thus its physical matrix is expected to be different from corn and some other agricultural materials. Accordingly, areas of modification recommended for using the AOCS Method Am 5-04 to measure oil content in DDGS are summarized in this communication.
Technical Abstract: A previous study at author’s lab showed that the AOCS official method Am 5-04, based on filter bag technology developed by Ankom Technology Inc. has to be modified in order to have accurate measurement of oil content in distillers dried grains with solubles (DDGS). The areas of modification recommended for using AOCS Method Am 5-04 to measure oil content in DDGS include: 1) Grind sample to a particle size of 0.71 mm or less; 2) Record weight of each individual filter bag; 3) Extend drying time to 4 hr at the pre-extraction stage; 4) chose hexane instead of petroleum ether; 5) Extend drying time to 60 min at the post-extraction stage; and 6) modify the calculation equation to reflect reduction of the filter bag weight from the original sample weight.