EFFECT OF pH STABILITY ON ALPHA AMYLASE EXTRACTED FROM Aspergillus niger ON STARCH FROM LOCAL RICE IN GHANA
CHRISTIAN NYARKO
School of Medical Sciences, College of Health and Allied Sciences, University of Cape Coast (UCC), Cape Coast, Ghana.
JOSEPH A. MILLS
Department of Biomedical Sciences, School of Allied Health Sciences, College of Health and Allied Sciences, University of Cape Coast (UCC), Cape Coast, Ghana.
JOHN K. AFORTUDE
Department of Biomedical Sciences, School of Allied Health Sciences, College of Health and Allied Sciences, University of Cape Coast (UCC), Cape Coast, Ghana.
NAZIR KIZZIE
Department of Biochemistry, School of Biological Sciences, University of Cape Coast (UCC), Cape Coast, Ghana.
CALEB M. AGBALE
Department of Biochemistry, School of Biological Sciences, University of Cape Coast (UCC), Cape Coast, Ghana.
SAMUEL BADU NYARKO *
School of Medical Sciences, College of Health and Allied Sciences, University of Cape Coast (UCC), Cape Coast, Ghana.
*Author to whom correspondence should be addressed.
Abstract
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 (t1/2) and inactivation rate constant (kd) 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 t1/2 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 kd values ranges from 0.0780 to 0.0814 min-1 while the t1/2 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)
Keywords: Alpha amylase enzyme, half- life, activation energy, kinetic stability.