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Purification and thermostability of β-galactosidase (lactase) from an autolytic strain of Streptococcus salivarius subsp. thermophilus

Published online by Cambridge University Press:  01 June 2009

Byeong-Seon Chang  and
Raymond R. Mahoney
Byeong-Seon Chang
Affiliation:
Department of Food Science and Nutrition, Massachusetts Agricultural Experiment Station, University of Massachusetts, Amherst, MA 01003, USA
Raymond R. Mahoney
Affiliation:
Department of Food Science and Nutrition, Massachusetts Agricultural Experiment Station, University of Massachusetts, Amherst, MA 01003, USA
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Summary

β-Galactosidase from an autolytic strain of Streptococcus salivarius subsp. thermophilus was purified 109-fold to near homogeneity. The yield of purified enzyme was 41% and the specific activity was 592 0-nitrophenyl β-D-galactopyranoside U/mg at 37 °C. Two isozymes were present, but only one subunit was detected, having a mol. wt of 116000. Enzyme stability was 37–83 times greater in milk than in buffer in the range 60–65 °C. At 60 °C the half-life in milk was 146 min. Denaturation in buffer was first-order, but in milk the overall reaction order with respect to enzyme concentration was ˜ 0·5. The activation energy for denaturation was 453 kJ/mol in milk and 372 kJ/mol in buffer. In milk the activation energy for lactose hydrolysis was 35·1 kJ/mol.

Type
Original Articles
Information
Journal of Dairy Research , Volume 56 , Issue 1 , February 1989 , pp. 117 - 127
Copyright
Copyright © Proprietors of Journal of Dairy Research 1989

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References

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