Optimization of C/N ratio of the medium and Fermentation conditions of Ethanol Production from Tapioca Starch using Co – Culture of Aspergillus niger and Sachormyces cerevisiae

Studies on Co-Culture fermentation of tapioca flour as the substrate symbiotic strains of starch digesting Aspergillus niger and non starch digesting and sugar fermenting Saccharomyces Cerevisaie in a batch fermentation. The effect of Carbon to Nitrogen (C/N) ratio of the fermentation medium on ethanol concentration and biomass was investigated. The optimum C/N ratio of the fermentation medium was found to be 35.2.which gave a maximum ethanol concentration of 8.85 g/l. Experiments based on Central Composite Design (CCD) were conducted to study the effect of pH, temperature and substrate concentration on ethanol yield from pretreated tapioca flour and the above parameters were optimized using response surface methodology (RSM). The optimum values of pH, temperature and substrate concentration were found to be 5.5, 30°C and 60 g/l respectively. The tapioca flour solution equivalent to 6% initial starch concentration gave the highest ethanol concentration of 8.9 g/l after 48 h of fermentation at optimum conditions of pH and temperature. Logistic model was used for growth kinetics and Leudeking – Piret model was used for product formation kinetics.