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 Mg2+ and Ca2+. The effect of solvents and
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.