Influence of nitrogen sources on ethanol production by Saccharomyces Spp in the presence of formic acid

Abstract

Formic acid is one of the major inhibitory compounds present in hydrolysates derived from lignocellulosic materials, the presence of which can significantly hamper the efficiency of converting available sugars in the hydrolysates to bioethanol. The influence of different nitrogen sources supplemented media on bioethanol fermentation with Saccharomyces spp in the presence of formic acid was studied. The addition of ammonium sulphate and urea significantly increased cell number, glucose utilization, ethanol and glycerol production when compared with control media. It was observed that supplementation with nitrogen sources contributed assimilable nitrogen for the yeast strains growth when stressed with formic acid. The best concentration of nitrogen to be utilized by yeast was found to be 0.80 gN/L. The maximum cell numbers were 8.17± 0.23x 10⁷ and 8.68± 0.16x 10⁷ cells/mL for ammonium sulphate medium while control had the least of 4.00± 0.20x 10⁷ and 4.97± 0.08x 10⁷ cells/mL for S. cerevisiae NCYC2592 and S. arboricolus 2.3319 respectively. Ethanol accumulation increased with the consumption of glucose. The maximum ethanol production were 20.49 ± 1.24 and 19.74± 0.89 g/L using ammonium sulphate for S. cerevisiae NCYC2592 and S. arboricolus 2.3319 respectively. There was significant difference in ethanol production when the nitrogen sources were compared with the control medium (p< 0.05). The highest glycerol produced were 2.21 ± 0.04 and 3.11± 0.05 g/L using ammonium sulphate for S. cerevisiae NCYC2592 and S. arboricolus 2.3319 respectively. The conclusion was that yeast tolerance to formic acid and ethanol production could be achieved when fermentation medium is supplemented with nitrogen sources specifically ammonium sulphate.

Keywords: Lignocellulose, inhibitors, Saccharomyces, fermentation, yeast, biofuel