Production, Optimization and Characterization of an Acid Protease From Filamentous Fungi by Solid-state Fermentation

Abstract Acid proteases represent an important group of enzymes, extensively used in food and beverage industries. There are a diversification of food industries and thus an increasing demand for biocatalysts capable of adapting the industrial extreme environments. These demands can be covered by a plant and animal proteases; however there is a shortage to meet the present industrial demands. This necessitates the search for an alternative acid protease sources from fungi. The fungal isolates were recovered from grape and dairy farm soil using potato-dextrose Agar. The fungi were further screened for protease production based on the hydrolysis of clear-zone on skim-milk agar media. The potential fungi were then subjected to secondary screening under solid-state fermentation. After primary and secondary screening, the potential fungus (isolate Z1BL1) was identified to the genus level by combination of macroscopic and microscopic morphological study. The growth condition and media composition for potential fungal isolate (Z1BL1) was further optimized under solid-state fermentation. The crude enzyme produced from isolate Z1BL1 was characterized after partial purification by acetone and ammonium sulphate precipitation. A total of 9 fungal isolates were showed protease production in primary and secondary screening, however 1 potential isolate (Z1BL1) was selected for further study based on its protease activity. The potential fungus, isolate Z1BL1 was identified to the genus Aspergillus based on their morphological features. The optimization of media composition and growth conditions for acid protease production from Z1BL1 were slightly increased the protease activity. The acetone precipitated enzyme exhibited the maximum activity at 50 0C and pH 5 with stability at pH 4-6 and temperature 40-60 0C. Thus based on the above findings, the acid protease produced from Aspergillus was shown suitable enzyme characteristics required in industry and could be a candidate to be applicable in food industry after further purification by high resolution techniques.