Bioethanol Production Process using the Non-conventional Yeast Candida tropicalis

To simplify the fermentation process by eliminating the separate saccharificationstep, numerous genetically engineered S. cerevisiaestrains capable of secreting glucoamylase and /or alpha-amylase have been developed. This work undertakes a different approach to eliminate the saccharificationstep. The culture medium is supplemented with alpha-amylase and the fermentation of starch to ethanol is done by the non-conventional yeast Candida tropicalis. Yeast cells are free or immobilized in a supporting substrate like calcium alginate. Products other than ethanol are also recovered after fermentation; which makes this process more economically feasible. Our interest inC. tropicalisis based on its ability to metabolize a large variety of carbon on which it grows as a sole carbon and energy source, generating high biomass yields since its metabolism becomes purely oxidative when enough oxygen is supplied in the culture medium. Supplementation of the starch medium with a-amylase is sufficient to drive the fermentation of starch to ethanol by C. tropicalis. These results show that a recombinant C. tropicalis producing a-amylase is valuable for ethanol production from starch-rich plant byproducts. This fermentation process demonstrated a reduction in ethanol production costs. We were able to reach ethanol yields comparable to those obtained by some of the best systems such as those using cell surface-engineered S. cerevisiae displaying both alpha-amylase and glucoamylase. This non-conventional yeast species brings more economical value to both first generation (cereal grains) and second generation (lignocelluloses) feedstock. It is feasible to add further value to this process by integrating fermentation co-products that are essential to the profitability of the fuel ethanol business.