Cold-active beta-galactosidase from Arthrobacter psychrolactophilus strain F2 was overexpressed in Escherichia coli using the Cold expression system and the recombinant enzyme, rBglAp, was characterized. The purified rBglAp exhibited similar enzymatic properties to the native enzyme, e.g., (i) it had high activity at 0 degrees C, (ii) its optimum temperature and pH were 10 degrees C and 8.0, respectively, and (iii) it was possible to rapidly inactivate the rBglAp at 50 degrees C in 5 min. Moreover, rBglAp was able to hydrolyze both ONPG and lactose with K,,, values of 2.7 and 42.1 mM, respectively, at 10 degrees C. One U of rBglAp could hydrolyze about 70% of the lactose in 1 ml of milk in 24 h, and the enzyme produced trisaccharide from lactose. We conclude that rBglAp is a cold-active enzyme that is extremely heat labile and has significant potential application to the food industry. (C) 2007 Elsevier Inc. All rights reserved.