Abstract

Pectinase was produced from a culture of Aspergillus niger, Aspergillus fumigatus and Aspergillus flavus. Pectinase synthesis was achieved using mango (Mangifera indica) pectin extract as an inducer during pectinolytic fungi isolation while submerged fermentation process was carried out using ground mango peels as the sole carbon source. Substrate fermentation was evaluated within seven days by monitoring the pectinase activity every 24 h. The highest pectinase secretion was obtained from A. niger and A. fumigatus after 92 h (day 4) of incubation, while in A. flavus, it was after 120 h (day 5). Crude enzyme extracts from the three organisms were partially purified by a combination of ammonium sulphate precipitation and dialysis with an approximately two-fold purification of the pectinase and a yield of 5.4, 7.66 and 5.99% for A. niger, A. fumigatus and A. flavus, respectively after dialysis. The specific activities of 1.62, 1.79 and 1.86 U/mg for A. niger, A. fumigatus and A. flavus enzymes were calculated, respectively. Pectinase from A. niger and A. fumigatus had pH and temperature optima of 5.0 and 40°C, respectively, while that from A. flavus had pH and temperature optima of 5.0 and 45°C. The Michealis constant, K_m and the maximum velocity, V_max determined from Lineweaver-Burk plots of initial velocity data at different concentrations of the mango pectin extract were 0.357 mg/ml and 35.34 U; 0.156 mg/ml and 68.0 U; and 0.261 mg/ml and 60.61 U; for the enzymes from A. niger, A. fumigatus and A. flavus, respectively. The results suggest that mango peels can be used for value added synthesis of pectinase, an important enzyme with numerous biotechnological applications.

Key words: Mango peels, mango pectin extract, pectinase, Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, submerged fermentation, partial purification, characterization.