Studies on the production of Glucose oxidase by Aspergillus terreus UniMAP AA-1

• Main Author: Ahmad Anas, Nagoor Gunny
• Format: Thesis
• Language: English
• Published: Universiti Malaysia Perlis (UniMAP) 2012
• Subjects: Glucose oxidase (GOx); Aspergillus niger; Penicllium sp.; GOx-producing strain; Aspergillus terreus UniMAP AA-1
• Online Access: http://dspace.unimap.edu.my/xmlui/handle/123456789/21605

Glucose oxidase (GOx) has found a wide range of applications in chemical, food, beverage, biotechnology and other industries. It is commonly extracted from Aspergillus niger and selected strains of Penicllium sp. Currently there is a growing need to find alternative sources of this enzyme due to some drawbacks associated with A.niger and Penicllium sp. In this work, a novel GOx-producing strain, Aspergillus terreus UniMAP AA-1, was isolated from soil of Agrotech Research Centre, Sg Chucuh, Perlis.The screening tests for the GOx-producing strain were carried out on the basis of color development test by using agar plate containing o-anisidine and horseradish peroxidase. The screened strain was identified morphologically using light microscope and Scanning Electron Microscope (SEM) and further verified by molecular level identification. The strain was identified as a predominant extracellular GOx producer and exhibits a pelleted morphology in fermentation culture. These findings offer a new alternative to the existing GOx-producing strains which are known to be associated with few drawbacks. Subsequently, a sequential optimization based on statistical design and one-factor-at-a-time (OFAT) method was employed to optimize the production of extracellular GOx from the potential strain. Plackett-Burman design indicated glucose as the most influential variable followed by NaNO3, CaCO3, and peptone on the GOx activity; while KH2PO4, MgSO4.7H2O and FeSO4.7H2O showed negative main effect on the enzyme activity. Based on the result, glucose, NaNO3 and CaCO3 were selected for further optimization studies. The influences of the three medium components were investigated with one-factor-at-a-time (OFAT) and these variables were subsequently optimized using a face centered central composite design (FCCCD). The optimum conditions were found to be 10.64% (w/v), 1.21% (w/v) and 5.22% (w/v) for glucose, NaNO3 and CaCO3 respectively and the enzyme activity was found to be 6.72 U/ml, which was about seven fold higher than that obtained in media before optimization. The oxygen and glucose consumption as well as hydrogen peroxide and gluconic acid production profiles of the crude enzyme are all in-line with typical GOx properties. The kinetic constant, Km of the crude enzyme for its substrate, determined by direct fits of Michaelis–Menten equation through nonlinear regression (with correlation value or R2 =0.98) using solver function in Microsoft Excel software, gave the value of within the range of 7.5-15 mM. The result indicates substrate specificity of the crude enzyme towards β-D glucose (substrate) and demonstrated the tight binding of the crude enzyme with its substrate.