Characterization and stability of proteases from Penicillium sp. produced by solid-state fermentation

Investigations were carried out to characterize the protease produced by a wild strain of Penicillium sp. in solid-state fermentation (SSF). Defatted soybean cake was used as carbon and nitrogen source and solid matrix for SSF. The enzyme was produced at 28 °C using defatted soybean cake supplemented with 0.2 mol/l citrate–phosphate buffer and with an initial pH and substrate moisture of 5.0 and 55% (w/w), respectively. Optimum temperature for enzyme activity in the crude extract was 45 °C at a slightly acidic pH (6.5). The studies on pH stability showed that the enzyme was stable in a range of pH 6.0–9.0 and the effect of the inhibitors showed it to be possibly a serine protease. Stability studies revealed temperatures around 35–45 °C. The activity was reduced in the presence of Co2+, Mg2+ and Zn2+ ions, while the presence of Ca2+ and Na+ resulted in a discreet increase in proteolytic activity. The enzyme presented good stability towards oxidizing agent. The crude enzyme preparation was compatible with commercial detergents, retaining their 50–60% activities. The results demonstrated the importance of solid-state fermentation for the production of protease using defatted soybean cake as substrate, which offer significance benefit due to cheaper cost and abundant availability.