Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2010
Publication Date: 5/28/2010
Citation: Liu, K. 2010. Selected factors affecting crude fat analysis of distiller dried grains with solubles (DDGS) as compared with ground corn. Cereal Chemistry. 87(3):243-249.
Interpretive Summary: With increasing production of distiller dried grains with solubles (DDGS), both the fuel ethanol and the animal feed industries are demanding standardized protocols for characterizing product quality and determining market values. There are a few official methods for measuring crude oil/fat content in grains and feed. However, the most appropriate methods for DDGS analysis are yet to be fully developed. In this study, a rapid method based on high temperature solvent extraction (AOCS Approved Procedure Am 5-04) was used for measuring crude oil content in ground corn (GC) and resulting DDGS. Several factors, including sample type (GC and DDGS), sample origin or ethanol plant number (1, 2 and 3), sample particle size (original, <0.71 mm, and <0.50 mm mesh openings, size reduction achieved through grinding and sieving), solvent type (petroleum ether and hexane), extraction time (30 and 60 min), and drying time after extraction (30 and 60 min), were investigated by a complete factorial design. The objective was to determine these factors for affecting crude oil analysis of DDGS as compared with ground corn. The present study shows that using the approved AOCS procedure (Am 5-04) all factors studied had significant effects on crude oil content of measured samples. There were also significant interactions among some factors. More specifically, particle size had no effect for GC but it had a significant effect for DDGS. Solvent type had no effect for GC, but it had a significant effect for DDGS having shorter drying time after extraction. Extraction time had a significant effect for GC, but for DDGS, a significant effect was observed only on samples with larger particle size. Drying time had no effect for GC, but it had a significant effect for DDGS with larger particle size. Accordingly, for a unified procedure on both types of samples (GC and DDGS) is recommended, which includes: 1) reduce sample particle size to pass through at least U.S. standard mesh No. 25 (0.71 mm opening), 2) use petroleum ether or hexane, 3) extraction time should be 60 min, and 4) drying time should be 60 min. The most significance of the present study lies in that it first reports the effect of particle size on measurement of crude oil content in DDGS, and that measuring oil content of DDGS without further reduction of sample particle size tends to give lower estimate values. It also suggests the need for similar confirmation by any other methods based on solvent extraction.
Technical Abstract: With increasing production of distiller dried grains with solubles (DDGS), both fuel ethanol and animal feed industries are demanding standardized protocols for characterizing its quality. AOCS Approved Procedure (Am 5-04) was used for measuring crude oil content in ground corn (GC) and resulting DDGS. Factors, including sample type (GC, DDGS), sample origin (ethanol Plant 1, 2, 3), sample particle size (original, <0.71 mm, <0.50 mm mesh openings), solvent type (petroleum ether, hexane), extraction time (30, 60 min), and post-extraction drying time (30, 60 min), were investigated by a complete factorial design. For GC, only sample origin and extraction time had significant effects (p < 0.05) on oil values measured, but for DDGS, besides the two factors, sample particle size, solvent type and drying time also had significant effects. Among them, particle size affected most. On average, the measured oil content in DDGS ranged from 11.11% (original particle size), to 12.12% (< 0.71 mm) and to 12.55% (<0.50 mm). For measuring oil contents of DDGS, particle size reduction, 60 min extraction, and 60 min drying are recommended. This newly reported effect of DDGS particle size on crude oil analysis suggests the need for similar confirmations using other analytical methods.