Production, purification, and characterization of α-amylase from Aspergillus niger, Aspergillus flavus and Penicillium expansum using cassava peels as substrate

Abstract

Cassava peels are waste generated from cassava processing and are mostly disposed of in Nigeria by dumping indiscriminately in landfills/waste dumps where they remain as huge mounds and constitute nuisance to the environment. This study was carried out using cassava peels as substrate for the production of α – amylase from three fungi (Aspergillus flavus, Aspergillus niger and Penicillium expansum) selected from twelve microbial isolates obtained from biodegrading cassava peels. The fungi were isolated using cassava peel agar medium and the α – amylase was produced by the solid state fermentation process. The α – amylase was assayed by measuring the decrease in staining power of starch with iodine reagent at 620nm and purified by using Sephadex G-100 and Sephadex C-50. The α – amylase was characterized by examining the effect of temperature, stability at 70^oC, pH, substrate concentration, metal ions and EDTA. The results show that the purification fold and specific activity were 95.727, 1.053 Units/mg protein; 81.830, 0.982 Units/mg protein and 85.784, 0.686 Units/mg protein for A. flavus, A. niger and P. expansum respectively. The optimum temperature and pH were 45^oC and 4.5 respectively. It was observed that the α – amylase still retained some activity after heating at 70^oC for 35 min. The α – amylase activity increased with increase in substrate concentration and metal ion concentration (Na⁺, K⁺, Mg²⁺ and Ca²⁺) but decreased with increase in heavy metal ion concentration (Hg²⁺ and Pb²⁺) and EDTA.

Key words: Cassava peels, α – amylase, fungi, starch and Sephadex C – 50.