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Enhanced Thermostability of Lactase ( Escherichia coli ) in Milk
Author(s) -
MAHONEY R.R.,
WILDER T.
Publication year - 1987
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1365-2621.1987.tb05916.x
Subject(s) - denaturation (fissile materials) , thermostability , chemistry , mole , isozyme , chromatography , enzyme , biochemistry , nuclear chemistry
Denaturation of lactase in phosphate buffer was a first‐order process with a half‐life of 1.12 min at 60°C. Denaturation in milk was a biphasic first‐order process with a half‐life of 115 min at 60°C. Electrophoresis, isoelectric focusing and kinetic analysis all indicated the presence of two isozymes. The minor isozyme exhibited 9% of the total activity and was less thermostable in milk than the major isozyme. In the temperature range 53.5–60°C, the rate of denaturation of the major isozyme in milk was more than 100 times less than the rate in buffer. Arrhenius plots of denaturation in milk and buffer were biphasic. Above 56°C, E a denaturation in milk and buffer was 187 Kcals/mole and 19.8 Kcals/mole, respectively; below 56°C E a denaturation in milk and buffer was 36.8 Kcals/mole and 158 Kcals/mole, respectively.