Leaching and characterization of Rhizopus oligosporus acid protease from solid-state fermentation

For leaching of the acid protease produced by Rhizopus oligosporus in rice bran, a leaching solution of pH 7 gives optimal recovery, although the enzyme is more stable at pH 4. A contact time of 60 min is sufficient for extraction. Recovery is enhanced by NaCl. A ratio of leaching solution to bran of 10 ml g(-1) gives the best balance between the fraction of the enzyme recovered and the protease concentration in the leachate. Drying of the fermented substrate prior to leaching did nor improve recovery. The highest acid protease recovery achieved was 20.7 units of protease activity (PU) per g initial dry weight of substrate (IDS). The acid protease produced by R. oligosporus is active between pH 1.5-5 with optimal activity at pH 2. It exhibits maximum activity at 60 degrees C bur is not stable at this temperature.