PHYTOSTEROL COMPOSITION AND YIELD OF OIL FROM FRACTIONS OBTAINED BY SIEVING AND ELUTRIATION OF DISTILLERS DRIED GRAINS WITH SOLUBLES (DDGS)

Authors: SRINIVASAN, RADHAKRISHNAN - UNIV. OF ILLINOIS, URBANA; SINGH, VIJAY - UNIV. OF ILLINOIS, URBANA; Moreau, Robert; RAUSCH, KENT - UNIV. OF ILLINOIS, URBANA

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2007
Publication Date: 7/10/2007
Citation: Srinivasan, R., Singh, V., Moreau, R.A., Rausch, K.D.,Tumbleson, M.E., Singh, V. 2007. Phytosterol distribution in fractions obtained from processing of distillers dried grains with solubles using sieving and elutriation. Cereal Chemistry 84:626-639.

Interpretive Summary: Most of the fuel ethanol made in the US is via the fermentation of corn in a "dry grind" process that yields one co-product, Distillers Dried Grains with Solubles (DDGS). DDGS is a good animal feed for ruminants, but its high content of fiber prevents it from being used as a feed for non-ruminants. In a previously published report, we described a two-step process which combines sieving and density separation to remove a significant amount of fiber from DDGS. Phytosterols are valuable cholesterol-lowering nutraceutical compounds that occur in high levels in corn fiber oil and at lower levels in other vegetable oils and in many other plant materials. In the current study we compared the levels of corn oil and phytosterols in the two DDGS fractions obtained by our previously-reported sieving and density separation process. We found that the oil content of the heavier low-fiber, high-protein fraction was 9.8% and the oil content of the lighter high-fiber fraction was 3.5%. The oil obtained from the lighter high-fiber fraction contained a higher concentration of phytosterols than the oil obtained from corresponding heavier fraction. However, the total quantity of phytosterols that can be recovered from the lighter faction was less than from heavier fraction. These results indicate that although both types of DDGS contain more phytosterols than are present in corn kernels, neither of these processing fractions contain enough phytosterols to consider them as cost-effective feedstocks to extract phytosterols. These results will be useful for researchers in the grain processing industry, researchers in the fuel ethanol industry, and those evaluating new uses for DDGS and other agricultural materials.

Technical Abstract: Separation of fiber from distillers dried grains with solubles (DDGS) provides two valuable coproducts: 1) enhanced DDGS with reduced fiber, increased fat and increased protein contents and 2) fiber. Recently, the elusieve process, a combination of sieving and elutriation was found to be effective in separating fiber from DDGS. Elutriation is the separation of particles by means of an upward flowing stream of fluid. Material elutriated by the air (lighter fraction) had higher fiber content than material that settled to the bottom of the elutriation column (heavier fraction). In this study, oil was extracted from fractions obtained by elusieve processing of a commercial sample of DDGS and the composition of phytosterol fatty esters, free phytosterols, and ferulate phytosterol esters in the oil was determined. The two smallest size categories and the biggest size category obtained by sieving of DDGS contained higher oil content than DDGS. The oil content in lighter fractions was less than oil content in the corresponding heavier fractions. When the 24T size category (869-2800 µm) was elutriated at an air velocity of 1.88 m/s, the oil content in lighter fraction was 3.5% and the oil content of 9.8% in the heavier fraction. Oil in the lighter fractions contained higher phytosterol content than the corresponding heavier fractions, but the total quantity of phytosterols that can be recovered from fiber coproduct was lower than that from enhanced DDGS.