Microbial Growth Kinetics in Isobutanol Production by Saccharomyces Cerevisiae

Abstract

Renewable sources of fuels are important for environmental sustainability. Biofuels are produced from renewable feedstocks through biological processes and can be found in the form of liquid, gas and solid. Isobutanol, a branched chain butanol isomer, is a type of biofuel that can be produced through the fermentation of biomass using microorganisms. In an aerobic fermentation, Saccharomyces cerevisiae (yeast) produced certain amount of isobutanol as by-product during the degradation of valine through the Ehrlich pathway. In the fermentation process, the determination of growth kinetics gives a better explanation regarding the relationship between specific growth rate and the concentration of a substrate. Kinetic coefficients are useful in providing information regarding the progression of either the chemical or biological reaction occurring in a system. In this study, the microbial growth kinetics, glucose utilisation and isobutanol productivity were investigated. The growth kinetics coefficients were determined by the Monod's model while the Ledeuking-Piret's model were used in investigating the parameters involved in substrate's consumption and product's formation. The maximum specific growth rate, μmax and the substrate saturation constant, Ks were determined from the slope and interception point (a plot between 1/μ and 1/S) during 48 h of fermentation period. The value of μmax and Ks obtained were 0.74 h-1 and 57 g/L. The isobutanol yield (YP/S), biomass yield (YX/S) and the correlation between isobutanol production and yeast growth (YP/X) were found to be 4.79 mg/g, 0.1 g/g and 49.4 mg/g. The Monod's and Leudeking-Piret's models were found to be suitable to represent the experimental data of growth kinetics and product's formation kinetics in this study.