Czech J. Food Sci., 2008, 26(4):284-290 | DOI: 10.17221/31/2008-CJFS

Isolation and identification of a strain producing cold-adapted β galactosidase, and purification and characterisation of the enzyme

Wen-Yu Liu^{1, 2}, Ying-Wu Shi¹, Xin-Qin Wang^{1, 3}, Yun Wang¹, Chang-Qing Wei², Kai Lou¹

¹ Xinjiang Institute of Microbiology, Xinjiang Academy of Agricultural Sciences, Urumqi, Xinjiang, P. R. China

² College of Food, Shihezi University, Shihezi, Xinjiang, P. R. China

³ College of Food Science, Xinjiang Agricultural University, Urumqi, Xinjiang, P. R. China

Enzymes with high specific activities at low temperatures have potential uses in the food industry. Cold-adapted microorganisms are potentially useful sources of cold-active enzyme. To find cold-adapted β-galactosidase, we isolated several cold-adapted microorganisms from glacier zone soil. One cold-adapted β-galactosidase producing strain was obtained. The biochemical characteristics and the results of 16S rDNA sequencing identified the strain as Rahnella aquatilis. The enzyme was purified by column chromatography after which a single protein band migrating near 60 kDa was observed by means of SDS-PAGE. The β-galactosidase was optimally active at 35°C and at pH 6.5 when assayed with o-nitrophenyl-β-D-galactopyrano-side as substrate. The enzyme activity was sensitive to temperatures above 40°C and was undetectable at 45°C. Metal ions Mn²⁺and K⁺ activated the enzyme while Cu²⁺, Zn²⁺, Fe³⁺, and Al³⁺ inhibited the activity. The enzyme was also assayed for lactose hydrolysis. When milk is treated with the enzyme at 30°C for 2 h, the degree of lactose hydrolysis can reach 80%. It has, thus, potential applications in the food industry.

Keywords: psychrotrophic microorganism; cold-adapted β-galactosidase; lactose hydrolysis

Published: August 31, 2008  Show citation