Effect of process parameters and media on the production of ethanol by Scheffersomyces stipitis in shake flask fermentation

The medium composition and fermentation parameters play a critical role in the fermentation process. Therefore, in the present study, the effects of fermentation parameters (initial glucose concentration (IGC), inoculation ratio (IR), initial pH value (IPV), stirring rate (SR), and temperature (T)) and medium composition (yeast extract (YE) and peptone (PEP)) on bioethanol production from glucose by using Scheffersomyces stipitis in shake flask fermentation were studied, respectively. According to results, the highest ethanol yield (Y-P/S) was achieved to be 47.63% when IGC, IR, IPV, SR, T, and nitrogen concentrations were 15 g/L, 5% (v/v), 5.5, 150 rpm, 30 degrees C, 5 g/L YE, and 20 g/L PEP, respectively. Nevertheless, the best fermentation parameters were 15 g/L IGC, 5% (v/v) IR, 5.5 IPV, 150 rpm SR, 30 degrees C T, no YE, and 5 g/L of PEP, respectively. At these conditions, kinetic results including bioethanol production, Y-P/S, ethanol yield per biomass, maximum production rate, sugar utilization yield, and theoretical Y-P/S were 8.29 g/L, 47.26%, 5.08 g ethanol/g biomass, 0.41 g/L/h, 95.86%, and 92.49%, respectively. In conclusion, these results indicated that although the concentrations of ingredients (YE and PEP) used in the fermentation medium were considerably decreased from 10 and 20 g/L to 0 and 5 g/L, the kinetic results of the fermentation were preserved compared to the initial fermentation studies. Nevertheless, further improvement of the determined fermentation parameters could be performed in the bioreactor.