Dynamics of inhibition patterns during fermentation processes-Zea Mays and Sorghum Bicolor case study

Abstract

Recently ethanol production involved the processing and fermentation of sorghum and maize extracts. Sorghum and maize are cheaper, locally available and a substitute to imported barley malt. Large scale ethanol fermentation systems are usually hampered by instability, in the form of oscillations resulting from ethanol inhibition and the lag response of yeast cells to this inhibition. There is limited information regarding the mathematical nature of such inhibitions in the fermentation of sorghum and maize extracts. In the present work, mathematical models are developed to determine the nature of ethanol inhibition during the fermentation of sorghum and maize extracts. The models were sets of coupled ordinary differential equations based on a Monod type cell growth kinetic model that accounts for product inhibition. The Inhibition patterns considered were; Linear, Sudden Growth Stop and Exponential. The results obtained showed that there is product inhibition during ethanol fermentation using sorghum extracts, with inhibition patterns being Linear and Exponential. However, the results obtained from ethanol fermentation of maize extract also showed that there is product inhibition during ethanol fermentation using maize extracts, with inhibition patterns being Linear and Sudden Growth Stop. The obtained models described with high accuracy, 99% Confidence Interval the dynamics of substrate utilization, product formation and cell growth. These inhibitions which affect the high ethanol yields can be minimized by setting up an optimal control problem using the developed models and solved to determine the control variables that minimize the effect of such inhibitions during the fermentation of sorghum and maize extracts.