Production and characterization of an acid Protease from a local Aspergillus Sp. by Solid substrate fermentation

The study aimed at isolating a potential acid protease producing fungal strain from local soil source. The fungal strains were isolated from garden soil on the basis of clearance zone on casein-glycerol agar flooded by coomassie blue stain. Aspergillus sp. showing maximum clearance on casein agar plates (pH 5) was selected for further studies. Optimization of various factors influencing maximum enzyme production by Aspergillus sp. using solid state fermentation was investigated. Optimum fermentation conditions for enzyme production were substrate (wheat bran & gelatin; 1%, w/v), fermentation time (120 h), moisture content (20 %), growth pH (5.0) and temperature (30oC). Wheat bran supplemented with nitrogen sources viz., gelatin and potassium nitrate showed 15-17 % increase in enzyme productivity. However, supplementation with additional carbon sources or salt solution had no profound influence on enzyme productivity. The crude acid protease of Aspergillus sp. showed pH and temperature optima of 5 and 50°C respectively. An increased enzyme activity was observed in presence of Ca and Mg. The enzyme showed broad substrate specificity. Thermostability of this enzyme at 50°C for 30 min throws light on its potential for applications in food industries.