HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Interpretive Summary Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Chen, W. Articles by Zhang, H. Search for Related Content PubMed PubMed Citation Articles by Chen, W. Articles by Zhang, H.

Production, Purification, and Characterization of a Potential Thermostable Galactosidase for Milk Lactose Hydrolysis from Bacillus stearothermophilus

State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi 214122, China

¹ Corresponding author: weichen{at}jiangnan.edu.cn

β-Galactosidase, commonly named lactase, is one of the most important enzymes used in dairy processing; it catalyzes the hydrolysis of lactose to its constituent monosaccharides glucose and galactose. Here, a thermostable β-galactosidase gene bgaB from Bacillus stearothermophilus was cloned and expressed in B. sub-tilis WB600. The recombinant enzyme was purified by a combination of heat treatment, ammonium sulfate fractionation, ion exchange, and gel filtration chromatography techniques. The purified β-galactosidase appeared as a single protein band in sodium dodecyl sulfate-PAGE gel with a molecular mass of approximately 70 kDa. Its isoelectric point, determined by polyacryl-amide gel isoelectric focusing, was close to 5.1. The optimum temperature and pH for this β-galactosidase activity were 70°C and pH 7.0, respectively. Kinetics of thermal inactivation and half-life times for this thermostable enzyme at 65 and 70°C were 50 and 9 h, respectively, and the K_m and V_max values were 2.96 mM and 6.62 µmol/min per mg. Metal cations and EDTA could not activate this thermostable enzyme, and some divalent metal ions, namely, Fe²⁺, Zn²⁺, Cu²⁺, Pb²⁺, and Sn²⁺, inhibited its activity. Thiol reagents had no effect on the enzyme activity, and sulfhydryl group blocking reagents inactivated the enzyme. This enzyme possessed a high level of transgalactosylation activity in hydrolysis of lactose in milk. The results suggest that this recombinant thermostable enzyme may be suitable for both the hydrolysis of lactose and the production of galactooligosaccharides in milk processing.

Key Words: thermostable β-galactosidase • lactose • purification • hydrolysis

This article has been cited by other articles:

				W. Chen, H. Chen, Y. Xia, J. Yang, J. Zhao, F. Tian, H. P. Zhang, and H. Zhang Immobilization of recombinant thermostable {beta}-galactosidase from Bacillus stearothermophilus for lactose hydrolysis in milk J Dairy Sci, February 1, 2009; 92(2): 491 - 498. [Abstract] [Full Text] [PDF]