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Thermostability of yeast lactase (Kluyveromyces marxianus) in milk

Published online by Cambridge University Press:  01 June 2009

Raymond R. Mahoney  and
Teresa Wilder
Raymond R. Mahoney
Affiliation:
Department of Food Science and Nutrition, Massachusetts Agricultural Experiment Station, University of Massachusetts, Amherst, MA 01003, USA
Teresa Wilder
Affiliation:
Department of Food Science and Nutrition, Massachusetts Agricultural Experiment Station, University of Massachusetts, Amherst, MA 01003, USA
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Summary

The half-life (∼ 2 h) of commercial yeast lactase (Kluyveromyces marxianus) in milk at 45 °C was 20 times greater than in milk salts and 50 times greater than in phosphate buffer. K was a more effective stabilizer than Na, both in milk salts and buffer. Stability was markedly reduced by the absence of divalent cations. Lactose and caseinate both stabilized the enzyme about 5-fold in milk salts, but together they stabilized it almost 50-fold. At equimolar concentrations, galactose was almost as effective as lactose as a stabilizer, but glucose was much less effective and sucrose had no effect. Stability in milk was independent of enzyme concentration, but varied with concentration of milk solids, reaching a maximum at about 25% solids. In milk, enzyme denaturation was more sensitive to changes in temperature in the range 42–53 °C than in the range 30–40 °C. At a concentration of 10 O-nitrophenyl-β-d-galactopyranoside units/ml it took 19 min at 45 °C to achieve 80% hydrolysis of lactose in milk, compared to 87 min at 30 °C.

Type
Original articles
Information
Journal of Dairy Research , Volume 55 , Issue 3 , August 1988 , pp. 423 - 433
Copyright
Copyright © Proprietors of Journal of Dairy Research 1988

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