Different schemas of saccharification and fermentation for bioethanol production from Opuntia ficus-indica cladode flour with wild strains

Abstract

In the present work, two wild microorganisms were studied for saccharification and fermentation. A wild Acinetobacter pittii isolated from decaying cladodes (Opuntia ficus-indica) was capable of producing extracellular cellulases and a wild yeast Kluyveromyces marxianus isolated from termite was capable of producing alcohol. In Mexico, there are surpluses of cladode production and where it is essential to take advantage and use this carbon source for alcohol production due to currently fossil fuels depletion. Separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF) and semi-simultaneous saccharification and fermentation (SSSF) for cellulase and alcohol production using Opuntia ficus-indica cladode as a unique carbon source was evaluated. In SHF process the best conditions for FPase activity (Filter paper activity for total cellulases) were 37 °C and pH 6.5 obtaining 0.67±0.02 U/ml and 0.61±0.03 U/ml for Acinetobacter pittii and Kluyveromyces marxianus, respectively. For alcohol production, the best conditions were 40 °C and pH 5.5 obtaining 12.95±0.3 g/L with K. marxianus while A. pittii did not produce significant alcohol concentration. Both processes were made with agitation (200 rpm). The SSF process was made with both microorganisms inoculated at the same time at 37 °C and without agitation. The maximum FPase activity of 0.28±0.004 U/ml and the maximum alcohol concentration was 7.5±0.27 g/L. Finally, an SSSF was performed, initially with A. pittii at 37 °C and after 8 h K. marxianus was then inoculated with temperature switched to 40 °C, the all process was performed without agitation. The maximum FPase activity was 0.45±0.001 U/ml, and the maximum alcohol concentration was 11.7±0.02 g/L. There was a significant difference (ANOVA) between SHF and SSSF in alcohol production. The best process for FPase activity and alcohol production is separate hydrolysis and fermentation using only yeast Kluyveromyces marxianus.