Production, purification, immobilization, and characterization of a thermostable β-galactosidase from Aspergillus alliaceus.

A fungal strain isolated from rotten banana and identified as Aspergillus alliaceus was found capable of producing thermostable extracellular β-galactosidase enzyme. Optimum cultural conditions for β-galactosidase production by A. alliaceus were as follows: pH 4.5; temperature, 30 °C; inoculum age, 25 h; and fermentation time, 144 h. Optimum temperature, time, and pH for enzyme substrate reaction were found to be 45 °C, 20 min, and 7.2, respectively, for crude and partially purified enzyme. For immobilized enzyme-substrate reaction, these three variable, temperature, time, and pH were optimized at 50 °C, 40 min, and 7.2, respectively. Glucose was found to inhibit the enzyme activity. The K(m) values of partially purified and immobilized enzymes were 170 and 210 mM, respectively. Immobilized enzyme retained 43 % of the β-galactosidase activity of partially purified enzyme. There was no significant loss of activity on storage of immobilized beads at 4 °C for 28 days. Immobilized enzyme retained 90 % of the initial activity after being used four times.