Biochemical Properties and Stability Profile of Alpha-Amylase Produced by Aspergillus niger from Compost Soil

Abstract

This study investigated the biochemical properties and stability profile of α-amylase produced by Aspergillus niger isolated from compost soil collected in Obio/Akpor Local Government Area, Rivers State, Nigeria. The fungal isolate was obtained using standard serial dilution and culture techniques and was screened for amylase production using starch hydrolysis assays. Enzyme production was achieved through submerged fermentation using a defined nutrient medium, followed by partial purification using ammonium sulphate fractionation and gel filtration chromatography. The partially purified enzyme was characterised to determine its biochemical behaviour under varying physiological conditions. The results showed that α-amylase activity increased with substrate concentration, reaching optimum activity at higher starch levels before plateauing, suggesting substrate saturation. The enzyme exhibited maximum activity at temperatures between 60 °C and 70 °C, indicating moderate thermostability. pH optimisation studies revealed that the enzyme performed optimally under near-neutral to slightly alkaline conditions, while strongly acidic and alkaline environments markedly reduced activity. Thermal stability analysis showed that enzyme activity was maintained at moderate temperatures but declined after prolonged exposure to elevated temperatures. Metal-ion studies demonstrated that Cu2+ enhanced enzyme activity, whereas Ca2+, Zn2+, and EDTA inhibited enzymatic performance. The findings suggest that α-amylase from compost-derived Aspergillus niger exhibits promising biochemical characteristics, including reasonable stability under industrially relevant conditions. These properties indicate potential applicability in starch processing and related biotechnological industries. However, further purification, molecular characterisation, and process optimisation are required to fully establish its industrial viability.