Corn fiber is a coproduct of the corn wet milling industry. It is a mixture of corn kernel hulls and residual starch not extracted during the wet milling process. Corn fiber is composed of approximately 40% hemicellulose, 12% cellulose, 25% starch, 10% protein, 3% oil, and 10% other substances such as ash and lignin (Singh et al. 2003). Approximately 6.3 x 106 dry tons of corn fiber is produced annually in the United States. Typically 4.51b of corn fiber is obtained from a bushel (56 lb) of corn, which can be converted to about 3.0 lb of fermentable sugars (Ezeji et al. 2006). The major fermentable sugars from hydrolysis of corn fiber are glucose, xylose, and arabinose (Ezeji and Blaschek 2008a; Noureddini and Byun 2010). Small amounts of mannose (Ezeji and Blaschek 2008a) and galactose (Noureddini and Byun 2010) have also been measured in corn fiber hydrolysates.

Economically, it is important that these mixed sugars present in corn fiber hydrolysates be fermented to butanol for this renewable biomass to be used as feedstock for butanol produc­tion. Solventogenic Clostridium species have an added advantage over many other cultures as they can utilize both hexose and pentose sugars (Ezeji et al. 2007a, b; Ezeji and Blaschek 2008a) released from lignocellulosic biomass upon hydrolysis to produce butanol. C. beijer — inckii BA101 effectively ferments detoxified dilute acid pretreated corn hydrolysates to produce butanol (Table 3.2; Qureshi et al. 2008a). Similarly, Parekh et al. (1988) produced butanol from hydrolysates of corn stover using C. acetobutylicum P262. Marchal et al. (1986), in addition, fermented acid pretreated corn stover hydrolysates to produce 12.8 g/L acetone — butanol using C. acetobutylicum NCIB644 (Table 3.2). In another development, Zhu et al. (2002) produced butyric acid, an intermediate ABE fermentation product, from acid hydro­lysates of corn fiber by Clostridium tyrobutyricum in a fibrous — bed bioreactor. This fermenta­tion process can improve butanol yield, reduce butanol production costs, and improve the economics of butanol fermentation. Importantly, butyric acid can easily be incorporated into fermentation medium and converted to butanol during ABE fermentation (Tashiro et al. 2004 ).