Saccharification of cassava waste by Trichoderma reesei for ethanol production

Abstract

Cultivation of T. reesei TISTR 3080 which produced both cellulase and amylase in cassava waste (15% wet w/v) supplemented with (NH₄)₂SO₄ for 3 days released 13.21 mg/ml of reducing sugar. After optimization of the conditions; 15% (wet w/v) cassava waste, 0.2% (NH₄)₂SO₄, pH 6.0, incubated at 35°C (150 rpm), 3 days; the reducing sugar increased to 14.07 mg/ml. To discontinue reducing sugar consumed by T. reesei, the incubating temperature was rapidly increased to 60°C. Addition of cassava waste into the culture incubated at 60°C, the reducing sugar increased to 17.59 mg/ml. Fermentation of this cassava waste hydrolysate which contained 13.62 mg/ml glucose to ethanol by S. cerevisiae for 72 h resulted in ethanol 1.91% (w/w) of cassava waste. T. reesei grown-cassava fiber separated from the cassava waste hydrolysate was also saccharified. Two steps method was performed: T. reesei cellulase production and hydrolysis of the cassava fiber by the cellulase produced. Non decontaminated cassava fiber suspended in sterile optimized nutrients for T. reesei cellulase production, then directly incubated without inoculation gave maximum endoglucanase (0.34 U/ml). The optimal nutrient concentrations and incubation conditions used for T. reesei cellulase production were 15% (wet w/v) cassava fiber, 0.3% (NH₄)₂SO₄, 0.4% KH₂PO₄, 0.025% MgSO₄.7H₂O, 0.05% yeast extract), pH 6.0, at 35°C (150 rpm) for 3 days, respectively. The endoglucanase produced (15.98 units) was used to saccharify the T. reesei grown-cassava fiber: 90% (wet w/v) at 60°C, pH 6.0 for 6 h. Then, cassava fiber hydrolysate which contained 54.60 mg/ml reducing sugar or 26.86 mg/ml glucose was fermented to ethanol by S. cerevisiae. Ethanol (1.84% w/w of fiber) was obtained after 72 h. By this procedure cassava waste was saccharified to glucose at 4.23% (w/w) of cassava waste, and ethanol at 3.11% w/w of glucose was produced.