Effect of immobilization on production of ethanol using yeast cells

Abstract

Sugar is converted to ethanol and CO2 by yeast during the fermentation process. Ethanol has various uses like it used as fuel, help in preserving biological sample, used as solvent, manufacture of acetaldehyde, ethanoic acid, etc. Use of yeast cells in fermentation industry on economic grounds proposes entrapment of yeast cell and their utilization. Immobilization of yeast cells offers many advantages as compare to free cells like easy recovery of product, its cost effectiveness, stability, yeast cells can reuse in further fermentation process etc. In this study, three yeast strain Saccharomyces cerevisiae NCIM 3570, Candida shehatae NCIM 3500, Dekkera naardenensis NCIM 3575 were immobilized using 3% Sodium alginate. The calcium alginate beads thus formed were used as inoculums for ethanol production independently where free cell inoculums of respective strain were taken as control. The initial glucose concentration in fermentation media for S. cerevisiae and D. naardenensis was 10% where as for C. shehatae it was 5% glucose along with 5% xylose. Amount of ethanol was estimated by HPLC analysis using Hiplex-H Agilent column having Column and Detector Temperature 57°C and 50°Crespectively, flow rate 0.7 ml/min, mobile phase 1 mM H2SO4 using refractive index detector. Also, viability of immobilized yeast cell stored in different condition like 4°C, room temperature, used bead at 4°C for 45 days was checked by plating on MGYP agar plates. Effect of immobilization on ethanol production was compared between both free cell and encapsulated cell. Ethanol concentration in immobilized S.cerevisiae was found to be higher (194.69) g/l as compared to the free cell (81.24 g/l). In case of D. naardenensis and C. shehatae the ethanol produced in immobilized cell is less as compare to free cell. Good numbers of colonies were found in case of 4°C, room temperature and one time-utilized beads stored at 4°C was checked after 45 days and found that the cells retained viability.