Biorefinery for bioethanol, lactic acid, xylitol and astaxanthin production from corn cobs
A biorefinery is an integrated process for biomass conversion to produce multiple products including fuels and chemicals. For successful developmentofbiorefinery, it is important toachieve the rational design of the total biorefinery system for high profitability with low environmental impact. In this view, we experimentally examined the feasibility of biorefinery for producing multiple products including bioethanol, xylitol, lactic acid and astaxanthin from corn cobs as a feed stock. The corn cobs were first hydrolysed by the dilute acid to obtain to xylose and its residues were then enzymatically hydrolyzed to glucose. By this treatment, hydrolysates containing approximately 27 g-xylose/l and 26 g-glucose/l were selectively obtained from 100 g-corn cobs/l. Using the hydrolysate containing xylose, approximately 18g/l xylitol was successfully produced by Candida magnolia. Thehydrolysate containingglucosewaseasilyutilized for bioethanol production by Saccharomyces cerevisiae. Simultaneous enzymatic saccharification and fermentation (SFF) was also effective to produce bioethanol and lactic acid from corn cob residues treated by dilute sulphuric acid, which mainly contain cellulose. It was also found that the hydrolysates containing xylose and glucose could be used as a favourable source for astaxanthin production using Xanthophyllomyces dentrohous. By incorporating the high value product such as astaxanthin into the biorefinery system, the economic feasibility of the biorefinery was greatly improved. Finally total process evaluation will be presented from the view points of profitability, energy consumption and environmental impact.