Bioconversion of Coffee Husk Cellulose and Statistical Optimization of Process for Production of Exoglucanase by Rhizopus stolonifer

Exoglucanase was produced using coffee husk, the by-product of coffee processing industries, as the sole carbon source using economical fermentation strategies like solid-state fermentation (SSF). The effects of process parameters such as pH, moisture and fermentation duration on exoglucanase synthesis was investigated using response surface methodology (RSM) based on three factors and five level central composite rotatable design (CCRD). Statistical analysis revealed moisture and fermentation duration has significant effect on the exoglucanase production. The optimized conditions were pH 6.7, moisture 43.2% and fermentation duration 99.8 hours. At these conditions, the predicted exoglucanase activity was 392.2 U/ml and the actual experimental value was 390.3 U/ml. The experimental value (390.3 U/ml) related well with the predicted one (392.2 U/ml) indicating the suitability of the model employed. The enzyme showed optimum activity at pH 6.0 and 40°C. The enzyme activity was enhanced in presence of Mg and Ca . The effect of solvents and 2+ 2+ detergents on the enzyme activity was also studied. The results indicate excellent scope of utilizing coffee husk as solid substrate for commercial production of exoglucanase employing Rhizopus stolonifer. This investigation is the first report of utilizing coffee husk for the production of exoglucanase and is significantly higher than the values reported for other potent fungi and bacteria and their utilization by biotechnological resources assume social, economic and industrial importance.