PARTIAL PURIFICATION AND CHARACTERIZATION OF ENDO-Β-GLUCANASES OF TWO NIGERIAN MALTED MAIZE VARIETIES (Published)
In this study, two Nigerian maize varieties (Farz 23 yellow and Farz 34 white) were malted at controlled experimental variables to determine the optimum conditions for the development of β-glucanases. The independent variable employed were steeping time, germination time and kilning temperature; and the measured (dependent variables) were diastatic power (DP), cold water extract (CWE) and hot water extract (HWE). Some properties of the two varieties were compared with those of sorghum (SK 5912). The properties of the grains were obtained as 1000-corn weight, (W) 241g and (Y) 248g; moisture content (%) 13.2, 12.8; germinative energy (%) 96, 92; germinative capacity (%) 99, 96; water sensitivity (%) 83, 82; broken kernel (%) 0.9, 1.1; protein (N×6.25%) 8.65, 9.02; and fat (ether extract, %) 3.70 and 4.14. The β-glucanases purified 2.59 and 0.56 folds for the yellow and white varieties respectively by a combination of 5M sucrose fractionation, ion exchange on Q-Sepharose and gel filtration on Sephadex G-200; with a yield of 0.8% (yellow) and 7.6% (white). The specific activity for the yellow maize enzyme was 0.312µ/mg and 0.381µ/mg for the white. The optimal condition for the glucanase activity for the white variety were 50oC and pH 5.0 and 7.0, while maximum stability was achieved at 40oC, pH 5.0 and 7.5 (16h); and for the yellow 60oC and pH 5.0 and maximum stability at 40oC, pH 6.0 (16h). The purified enzyme of the white variety was appreciably activated by Co2+, Mn2+ and Zn2+ gave inhibitory effects. The yellow variety glucanase activity was only enhanced by Mn2+ and fairly by Co2+. The yellow variety glucanase displayed remarkable wide substrate specificity and rapidly hydrolyzed amylose, amylopectin and starch. On substrate concentration the white maize enzyme indicated substrate enhancement on both Sigma cell type 20 and CMC. The Km values as obtained from Lineweaver-Burk plots for the white maize glucanase were 0.119 and 0.102mg/ml for CMC and Sigma cell respectively, and 0.072 and 0.0451mg/ml in same order for the yellow maize glucanase. Their corresponding Vmax were 3.7 and 3.5mg/ml/min for the white maize enzyme and 4.0 and 9.0mg/ml/min protein for the yellow maize enzyme. The very low Km values Sigma cell type 20 and CMC for the yellow indicates a high affinity of the yellow glucanase to the substrates. On overall assessment, the glucanases presents a promising application in the mashing conditions of the brew house.
Keywords: Characterization, Maize, Malting, Purification, β-glucanase