Amylase Production from Aspergillus sp Isolated from Dumpsite Soil Using Corn-Cob and Orange-mesocarp as a Substrate

Abstract

The increasing demand for sustainable and cost-effective enzyme production has driven research toward microbial fermentation using agro-residues as substrates. This study investigated dumpsite soils as reservoirs of α-amylase–producing fungi and evaluated corn cob and orange mesocarp as potential agro-residues for enzyme production. Fungi were isolated from soil samples (SA, SB, SC), enumerated, and identified based on macroscopic and microscopic characteristics. Proximate analysis of corn cob and orange mesocarp was carried out to determine their nutritional composition, while fermentation parameters including time, inoculum size, pH, carbon ratio, and nitrogen concentration were optimized to enhance α-amylase yield. The results showed that fungal counts ranged from 3.3 × 10⁴ to 4.2 × 10⁴ CFU/g across the soils, with sample SB recording the highest load. The isolates included Aspergillus, Rhizopus, Fusarium, and Penicillium species, with isolate SB2 exhibiting the highest α-amylase activity (26 mm clearance zone), while SB3 produced the least (5 mm). Proximate composition revealed that corn cob contained higher carbohydrate content (75.87%) compared to orange mesocarp (68.79%), whereas orange mesocarp exhibited higher ash, lipid, and protein contents. Fermentation studies showed that α-amylase yield increased with time, peaking at 48 h (51.2 U/ml) before declining. Optimum production parameters were obtained at pH 7.0 (47.6 U/ml) and a 3.0 mL inoculum size (53.3 U/ml), while supplementation with a 2:2% corn cob:orange mesocarp mixture supported maximum enzyme production (61.3 U/ml). Further optimization with 0.50% nitrogen supplementation resulted in the highest α-amylase yield of 68.3 U/ml. It is concluded that dumpsite soils harbor metabolically diverse fungi, and that low-cost agro-residues such as corn cob and orange mesocarp can be effectively utilized for α-amylase production under optimized fermentation conditions.