Extraction, Purification and Characterization of Protease from Aspergillus Niger Isolated from Yam Peels

Abstract

Protease was obtained from Aspergillus niger isolated from yam peels; a food waste, purified and characterized. Purification was achieved using ion exchange DEAE column and gel filtration (Sephadex G-200) chromatography. Effects of temperature; pH and production time on protease production were investigated. Also, physicochemical characteristics of the purified enzyme were investigated. The optimum production of protease was at temperature, pH and time of 37oC, 7.0 and 42 hrs respectively. The results showed that purified protease had more specific enzymatic activity than crude samples from Aspergillus Niger. whereas the specific activity of crude enzyme was 0.51 (U/mg), while the purified enzyme had an improved specific activity of 8.51 (U/mg).Optimum temperature and pH values of the purified protease were found to be 50°C and 10.0, respectively. pH stability of the enzyme ranged from 3.0- 12.0. At 3.0 and 10.0 it retained 70% and 60% of its activity after 5 hrs of incubation. Temperature stability ranged between 30oC and 90oC but most stable at 50oC retaining 94% of its activity after 1 h of incubation. The enzyme exhibited maximum activity on casein, among other protein substrates. EDTA, Cu2+, Fe2+, Mg 2+, and Ca2+ inhibited its activity while Na+ enhanced it. The enzyme was purified 16.60-fold, had a yield of 10.96 and the apparent molecular weight was 46.90 kDa. The study revealed that protease from A. niger can be exploited for protein conversion biotechnologies.