Assessment of intrinsic physico-chemical fermentation conditions (pH and total titratable acidity) on liberated reducing sugar by bacteria and bacteria-yeast coupled fermentation of selected lignocellulosic biomass to ethanol

Abstract

The study investigated the use of indigenous bacterial and yeast isolates to establish a single culture and a co-culture fermentation of selected lignocellulosic biomass (corn cobs and cassava peels) with bacteria and yeast. This was done to determine the effect of pH and total titratable acidity established by the activity these microorganisms on the liberation or reducing sugars available for bioethanol fermentation. The bacteria used in the study are: Bacillus macerans, B. subtilis and Micrococcus varians, while the yeast used is Saccharomyces cerevisae. The bacterial isolates were screened for amylase and cellulase activities and were found to express amylase relatively between 0.50-0.60 U/g and relatively between 0.040-0.0422 FPU for cellulase activity. The organisms were used in a single and co-culture fermentation trial for 20-days and intrinsic physic-chemical parameters (pH and Total titratable acidity) were examined at an interval of 5 days for 20 days. The pH of all the fermenting media were found to decrease progressively with time while the total titratable acidity and reducing sugar increased progressively with time. Highest reducing sugar was observed at pH values between 4.01 and 4.36 in both fermentation set up. At total titratable acidity between 0.133-0.146, the liberated reducing sugars were observed to reach a height of 45.46±0.00mg/g in the corn cob and cassava peels on the 20 th day of fermentation with M. varians. At P≥ 0.05, there was statistical significant difference in the liberated reducing sugar by both fermentation set up of bacteria and bacteria-yeast couple. The study demonstrated the pH and total titratable acidity trend established by spontaneous fermentation of selected lignocellulosic biomass and how the gradual fermentation process increased the acidity overtime and as such increased reducing sugar concentration were observed at reduced pH and increased titratable acidity. Therefore fermentation processes in which there is interest in increased reducing sugar such as bioethanol fermentation should be consciously monitored to continue until appropriate levels of acidity are reached for optimum liberation of reducing sugars which are essential for increased conversion efficiency into desired end product.