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Factors affecting the thermostability of β-galactosidase (Streptococcus salivarius subsp. thermophilus) in milk: a quantitative study

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

Enhanced stability of β-galactosidase (Streptococcus salivarius subsp. thermophilus) in milk is due to several milk components acting in concert. Milk salts stabilized the enzyme 3-fold compared to phosphate buffer. K+ was a better stabilizer than Na+. Omission of divalent cations, especially Mg2+, caused a marked drop in stability. Lactose stabilized enzyme stored in the frozen state but destabilized enzyme stored unfrozen. Caseinate stabilized the enzyme 8-fold in phosphate buffer but it stabilized 144-fold in the presence of lactose. In the presence of milk proteins, lactose was 25 times as effective as galactose and 100 times as effective as glucose at promoting stability; sucrose slightly destabilized the enzyme. Stability rose with increasing lactose concentration but declined with increasing enzyme concentration. In milk, soluble casein was the primary stabilizer; whey proteins and peptides had much less effect. Micellar casein had no effect on stability.

Type
Original articles
Information
Journal of Dairy Research , Volume 56 , Issue 5 , November 1989 , pp. 785 - 792
Copyright
Copyright © Proprietors of Journal of Dairy Research 1989

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References

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