Process optimization of temperature and substrate concentration on fermentation of fruit juices for brewery and bio-energy applications

Abstract

Optimization of fermentation processes on fruit juices as ethanol precursors is an important aspect of fermentation science for high-yield production of ethanol. The fermentation of fruit juices using soursop and sugarcane juices as substrates by Saccharomyces cerevisiae (yeast) was investigated to ascertain the effect of substrate concentration and temperature on the production of CO₂. Temperature and substrate concentrations were varied between 30-42^oC and 20-80% (v/v) respectively, during the fermentation process. The results show that though there was a range of temperature over which the yeast (Saccharomyces cerevisiae) was active, there was a narrow range of temperature (34-36^oC) over which its activity was at maximum. The initial increase in volume with temperature is expected to be a function of the increase in the average kinetic energy of the molecules. However, a further increase in temperature beyond 36^oC triggered the breakdown of the enzymatic structure due to increased thermal vibration of the enzyme molecules; decreasing further production of carbon dioxide. The increase in substrate concentration beyond 50% (v/v) with an attendant decline in the volume of CO₂ produced, suggests complete saturation of enzyme active sites at the initial stage of the reaction, such that further increase in substrate concentration could not lead to increased CO₂ production. However, there is a wide range of substrate concentrations over which the enzyme is active. The findings will therefore complement the existing database in the field of fermentation science and help in enzyme fermentation processes for breweries, bio-energy, and other applications.