Asian Journal of Microbiology and Biotechnology

Background: Alpha-amylases are one class of the amylase enzymes extensively synthesized in plants, animals, and microbes. They have been generally used in many industrial applications in a wide range of industrial processes such as food, pharmaceutical and detergent industries.

Due to their high catalytic and thermos stability property according to Yadav, fungal amylases are effectively applied in a wide range of industrial processes. These enzymes are affected by pH, temperature and/or substrates concentration.

Aim: This study aimed at determining the stability of alpha amylase from Aspergillus niger with varied pH conditions.

Methods: The kinetic stability of the enzyme was measured by determining its half-life (t_1/2) and inactivation rate constant (k_d) where pH was varied from 4.5 to 8.5 along with temperature from 50°C to 90°C. The inactivation rate constant was determined from the equation  while the t_1/2 was determined from=.

Results: The activation energy of inactivation was determined from the Arrhenius plot of inactivation. The protein concentration was estimated to be 2.57mg/ml by the Biuret method. The amylase isolated was thermos table with an optimum temperature of 70°C, optimum pH of 6.5 and an optimum substrate concentration of 0.26%. The Km was 0.13% while the Vmax was 1.0×10^-4g/ml. The k_d values ranges from 0.0780 to 0.0814 min^-1 while the t_1/2 values ranges from 8.51 to 8.78min and the results observed for pH 4.5, 6.5, 7.0, and 8.5 are 4.821 x10²J/mol, 9.342 x10²J/mol, 28.025 x10²J/mol and -9.362x10² J/mol respectively.

Conclusion: The stability of the enzyme is decreased by pH variation in the order pH 8.5 < pH 4.5 < pH 6.5 < pH 7.0 showing that the enzyme is stable in alkaline and acidic medium than in a neutral pH. The optimum substrate at which the reaction rate is independent of the substrate concentration was determined to be 0.26% (0.0026 g/ml)