Production of a Thermostable β-d-Galactosidase by Alternaria alternata Grown in Whey

摘要

In the course of exploring new microbial sources of extracellular β-d-galactosidase (EC. 3.2.1.23), Alternaria alternata was found to excrete elevated quantities of a thermostable form of the enzyme when cultivated in whey growth medium. Optimum cultural conditions for maximum enzyme production were a whey lactose concentration of 6%, supplementation of the medium with 0.050 M (NH4)2SO4, an inoculum size of 103 conidia per ml, and a cultivation time at 28 to 30°C of 5 days. The fungus utilized whey lactose for the production of the enzyme most efficiently, and the observed maximum yield, 280 nanokatals of hydrolyzed o-nitrophenyl-β-d-galactopyranoside per g of whey lactose, was comparable to maximum yields reported for certain commercial fungi. The optimum pH and temperature of the enzymatic reaction were 4.5 to 5.5 and 60 to 70°C, respectively, and the enzyme lost half of its activity when heated at 65°C for 84 min. These properties make the enzyme particularly suitable for processing acid and less-acid (pH 5 to 6) dairy products and by-products.