Enhanced bio-ethanol production via simultaneous saccharification and fermentation through a cell free enzyme system prepared by disintegration of waste of beer fermentation broth

Abstract

Current study illustrates the effect of high yeast cell density contained in the waste of beer fermentation broth (WBFB) on bio-ethanol production through simultaneous saccharification and fermentation (SSF). WBFB was disintegrated (DW) and comparatively evaluated against nondisintegrated WBFB (NDW) for bio-ethanol production at variant temperatures. Final bio-ethanol levels of 36.38 g/L and 18.65 g/L at 30 °C, 4.45 g/L and 43.23 g/L at 40 °C, and 2.32 g/L and 6.83 g/L at 50 °C were achieved with 20% NDW and DW, respectively, after 12 h. DW carried out the simultaneous saccharification and fermentation (SSF) process through cell free enzyme system and was capable of bioethanol production beyond the microbial growth temperature (>30 °C) of NDW system. The increase in sediment concentration in DW positively influenced the production capabilities of the system producing 43.23 g/L, 54.39 g/L and 62.82 g/L bio-ethanol with 20, 30 and 40% sediments at 40 °C, respectively. The retardation of bioethanol production at elevated temperature (50 °C) was expected to be caused by denaturing or digesting of certain enzymes as observed through SDS-PAGE. FTIR analysis also showed the appearance of a new band at approximately 1,590 cm−1 due to unfolding of polypeptide chains at 50 °C. The overall study reveals the positive influence of increased cell density on ethanol production and presents evidence for decreased fermentation beyond certain temperature limits.