Evaluation of fermentation kinetics of xylose to ethanol fermentation in the presence of acetic acid by <em>Pichia stipitis: </em> Modeling and experimental data comparison

Abstract

Acetic acid is one of the main inhibitor that shows negative impact on kinetics of sugar fermentation in the presence of <em>Pichia stipitis. </em> Unstructured kinetic model has been formulated that describes cell mass growth and ethanol production as a function of ethanol, oxygen, xylose and acetic acid concentration. Experiments have been carried out in batch mode with the acetic acid concentration varying from 3 to 12 gL^-1. Kinetic parameters are estimated for <em>Pichia stipitis</em> with various operating conditions of fermentation. Among all the kinetic parameters a great reduction in &mu;_MAX and increase in Y_P/X has been observed, which strongly affect the fermentation kinetics. Acetic acid presence in the fermentation lead to significant reduction in the maximum cell biomass concentration, reduction in xylose consumption rate, improvement in ethanol metabolic and reduction in ethanol production rate. This model describe physiological properties of PSA30 strain of <em>Pichia stipitis </em> and proposed models can be used to predict the influence of xylose, ethanol and acetic acid on cell growth and ethanol productivity in industrial fermentation.