HYDROLYSIS BY COMMERCIAL ENZYME MIXTURES OF AFEX-TREATED CORN FIBER AND ISOLATED XYLANS

Corn fiber is a coproduct produced during the corn wet-milling process and is similar to other high hemicellulose/cellulose-containing bioma ss such as grasses, straws, or bagasse, all of which represent potenti al fermentation feedstock for conversion into biofuels or other produc ts. Corn fiber was subjected to ammonia-explosion (AFEX) treatment to increase degradability and then enzymatically digested with a combined mixture of commercial amylase, xylanase, and cellulase enzyme prepara tions. Whereas the starch and cellulose components were converted sole ly to glucose, oligosaccharides represented 30-40% of the xylan degrad ation products. This enzyme mixture also produced substantial oligosac charides with xylans purified from corn fiber, corn germ, beechwood, o atspelt, or wheat germ. Commercial xylan-degrading enzyme preparations containing xylanase, xylosidase, and arabinosidase activities were th en used alone or in varying combinations to attempt to maximize degrad ation of these isolated xylans of differing chemical compositions. The results showed that oatspelt and beechwood xylans were degraded most extensively (40-60%) with substantial amounts of xylose, xylobiose, an d xylotriose as products depending on the enzyme combination used. Cor n fiber and wheat germ xylans, which contain large amounts of arabinos e and uronic acid sidechains, were poorly degraded and only small amou nts of arabinose and xylose and large amounts of pentamer or longer ol igosaccharides were produced by enzymatic degradation. The data sugges t that whereas enzymatic digestion of biomass hemicellulose does not p roduce toxic products, the process is not effective in producing a sui table fermentable substrate stream because of the low levels of monosa ccharides and high levels of oligosaccharides produced.