Production of lactic acid and ethanol by Rhizopus oryzae integrated with cassava pulp hydrolysis

Cassava pulp was hydrolyzed with acids or enzymes. A high glucose concentration (>100 g/L) was obtained from the hydrolysis with 1 N HCl at 121 °C, 15 min or with cellulase and amylases. While a high glucose yield (>0.85 g/g dry pulp) was obtained from the hydrolysis with HCl, enzymatic hydrolysis yielded only 0.4 g glucose/g dry pulp. These hydrolysates were used as the carbon source in fermentation by Rhizopus oryzae NRRL395. R. oryzae could not grow in media containing the hydrolysates treated with 1.5 N H₂SO₄ or 2 N H₃PO₄, but no significant growth inhibition was found with the hydrolysates from HCl (1 N) and enzyme treatments. Higher ethanol yield and productivity were observed from fermentation with the hydrolysates when compared with those from fermentation with glucose in which lactic acid was the main product. This was because the extra organic nitrogen in the hydrolysates promoted cell growth and ethanol production.