Optimising butyrate and lactate yields fermenting xylose in a mixed culture system

Abstract

Despite being the second most abundant monomer in the earth, xylose fermentation has not been studied as thoroughly as glucose fermentation. This work studies the pH effect in xylose fermentation, focusing on lactic and butyric acid production as medium chain fatty acids (MCFA) precursors. Continuous reactor operation showed that changes within a slightly acidic pH range (pH 4.5 to pH 6) affect to VFA production but not their distribution, being butyric and acetic acid the main products regardless the pH value, while lactic acid was only detected when xylose or butyric acid concentrations dropped. In contrast, xylose conversion was negatively affected by low pH values. The use of lactic acid as substrate was assessed in continuous and batch reactors, being consumed and mainly converted into butyric acid.