Submitted to: Yeasts International Symposium
Publication Type: Abstract Only
Publication Acceptance Date: March 28, 2002
Publication Date: N/A
Technical Abstract: Agricultural residues are abundant potential feedstocks for bioconversions to industrial fuels and chemicals. For example, every bushel of corn (maize) processed for sweeteners, oil, or ethanol generates nearly 7 kg of protein- and fiber-rich residues. Currently, these materials are sold for very low returns as animal feed ingredients. Conventional wet milling of corn generates a fibrous residue principally composed of the seed pericarp and adherent starch. Corn fiber is an abundant, readily available source of hexose and pentose polymers. Sugars derived from corn fiber are potential substrates for fermentation to numerous industrial chemicals, including fuel ethanol. Enzymatic saccharification of lignocellulose is an attractive alternative to chemical hydrolysis, because even mild acid hydrolysis generates fermentation inhibitors. However, corn fiber is particularly recalcitrant to digestion by commercially available enzymes. Nevertheless, a partial saccharification of corn fiber has been achieved using a crude mixture of enzymes from the yeast-like fungus Aureobasidium. At the same time, a novel two-stage fermentation process was developed to produce xylitol from corn fiber sugars, using the yeast-like fungus Pichia guilliermondii. Corn-based fuel ethanol production also generates large volumes of stillage residues, customarily folded into low-value animal feeds. Stillage residues were found to support the production of pullulan by Aureobasidium. In addition, unamended stillage was an ideal substrate for production of astaxanthin by the yeast-like fungus Phaffia rhodozyma. Ultimately, agricultural residues and other biomass sources may be exploited to provide most of our needs for fuels and chemicals.