Author
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Leathers, Timothy |
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Submitted to: Corn Utilization Conference Proceedings
Publication Type: Proceedings Publication Acceptance Date: 6/9/2004 Publication Date: 6/9/2004 Citation: Leathers, T.D. 2004. Utilization of corn germ residues. In: Proceedings of Corn Utilization Conference. June 7-9, 2004. Indianapolis, Indiana. CDROM. Interpretive Summary: Technical Abstract: A good deal of research concerns the production of fermentable sugars from certain corn residues, including stover, cobs, fiber, and bran. Surprisingly, very little work has been done on the utilization of corn germ residues. More than a million tons of corn oil are produced annually in the United States, generating at least a half million tons of defatted germ as a byproduct. More than 90% of corn oil is produced by wet milling, although dry milling operations also may include a tempering-degerming step. Corn oil is recovered from the germ by expelling and often solvent extraction. The defatted corn germ currently is folded into low value animal feeds. Defatted corn germ contains high-quality protein, starch, hemicellulose (arabinoxylan), and cellulose. Although the polysaccharide components can be chemically hydrolyzed, even relatively mild treatments such as dilute acid lead to the production of fermentation inhibitors including furfurals. Enzymatic saccharification of corn germ is a potential alternative. However, Hespell et al., reported that purified arabinoxylan from corn germ is only partially digested by a mixture of commercial enzymes (primarily from Trichoderma and Aspergillus), producing oligosaccharides but fewer monosaccharides [1]. Enzymes from Aureobasidium sp. strain NRRL Y-2311-1 subsequently were tested for the saccharification of defatted corn germ. Commercial defatted germ from wet milled corn was efficiently saccharified by a crude enzyme preparation from Aureobasidium with yields of up to 200 mg glucose, 140 mg xylose, and 130 mg arabinose per g germ [2]. These yields exceeded sugar composition estimates based on trifluoroacetic acid digestions. Substrates were boiled briefly to gelatinize starch, but no further pretreatments were necessary. Results from independent lots of defatted germ were similar. Enzymatically digested germ residues were enriched to 40% (w/v) protein [2]. Defatted germ from dry milled corn contained approximately 50% more starch than wet milled germ and was saccharified to produce up to 315 mg glucose per g germ with reduced yields of pentose sugars [2]. Optimal saccharifications required the use of crude enzyme preparations at 800 IU xylanase per g defatted corn germ. Nevertheless, Aureobasidium sp. strain NRRL Y-2311-1 produces up to 90,000 IU xylanase per L [3]. In conclusion, the enzymatic saccharification of starch, cellulose, and arabinoxylan in defatted wet mill germ appeared to be essentially complete. Under identical conditions corn fiber arabinoxylan was only about 50% hydrolyzed and cellulose was not attacked [3]. Defatted germ may be more susceptible than corn fiber to digestion by Aureobasidium enzymes because of structural differences, or because the process of oil extraction itself acts as a pretreatment. 1. Hespell RB, O'Bryan PJ, Moniruzzaman M, Bothast RJ (1997) Appl. Biochem. Biotechnol. 62: 87-97. 2. Leathers TD (2004) Biotechnol. Lett. 26:203-207. 3. Leathers TD, Gupta SC (1996) Appl. Biochem. Biotechnol. 59: 337-347. |
