Acid hydrolysis and fermentation of microalgal starches to ethanol by the yeast Saccharomyces cerevisiae

Many studies on the use of microalgal biomass to generate lipid and starch for production of transportation fuels assume ready conversion of starch to ethanol. However, few have shown data on this process. Here, biomass from the wall-deficient cells of Chlamydomonas reinhardtii mutant cw15 was sequentially treated with 70 °C ethanol and 60 °C hexane prior to sulfuric acid hydrolysis at 121 °C and 2 atm. Hydrolysis was monitored over time until no further starch breakdown was observed. An estimated 30% of the dry algal biomass was hydrolyzed for fermentation. This hydrolyzed starch was successfully fermented into ethanol by Saccharomyces cerevisiae to a maximum concentration of 0.87 ± 0.01% (m/v) at a maximum rate of 14 ± 1 mL/g h in 28 h. The observed yield coefficient of ethanol from glucose was 0.44 (g/g). Ethanol and what appeared to be glycerol were produced in equal proportions.