Process optimization for high gravity ethanol fermentation of cassava flour

Cassava is a potential feedstock for fuel ethanol. A “presaccharification combined with simultaneous saccharification and fermentation” process was used for high gravity ethanol fermentation of cassava flour, and the process was optimized. Cassava flour and water were mixed for 10–20 min with the ratio of 1∶2.0, and cooked at 85–90°C for 60 min, and then α-amylase (10U/g flour) was added and kept at 80–85°C for 60 min. Then the mixture was cooled to 60–65°C, adjusted to pH4.0–4.5, and then glucoamylase (150U/g flour) was added and kept at 60–65°C for 10 min. The mash was cooled to 30°C, and 0.8g/L of urea, 0.2 g/L of potassium dihydrogen phosphate and 0.5g/L of magnesium sulfate were added, and then activated yeast was inoculated by 1% and incubated at 28°C, 160 rpm for 72h. At the end of fermentation, the ethanol content reached 17.0% (v/v), the residual total sugar was 2.8% (g/v), the residual reducing sugar was 0.98% (g/v) and the starch utilization rate was 88.9%.