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Thermal inactivation kinetics of bovine cathepsin D

Published online by Cambridge University Press:  06 August 2001

MAURICE G. HAYES
Affiliation:
Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland
MICHAEL J. HURLEY
Affiliation:
Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland
LOTTE B. LARSEN
Affiliation:
Department of Animal Product Quality, Danish Institute of Agricultural Sciences, P.O. Box 50, DK-8830, Tjele, Denmark
CHRISTIAN W. HEEGAARD
Affiliation:
Protein Chemistry Laboratory, University of Aarhus, Science Park, DK 8000 Aarhus C, Denmark
ABDALLAH A. A. MAGBOUL
Affiliation:
Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland
JORGE C. OLIVEIRA
Affiliation:
Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland
PAUL L. H. McSWEENEY
Affiliation:
Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland
ALAN L. KELLY
Affiliation:
Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland

Abstract

Cathepsin D, the principal indigenous acid proteinase in bovine milk, is a lysosomal proteinase, which exists in milk in four forms, including the inactive zymogen procathepsin D. The thermal inactivation kinetics of bovine cathepsin D, isolated from spleen and milk, were studied under isothermal conditions, using a specific HPLC assay to determine residual activity. Inactivation of the blood enzyme preparation followed first order kinetics, with z-values in phosphate buffer (pH 6·7) and skimmed milk of 6·5 and 7·6 °C, respectively, the enzyme being far more stable in the latter environment. Inactivation kinetics of the enzyme purified from milk were more complex, and could be best approximated by a double exponential model. Again, stability was higher in milk than in buffer. The double exponential model may indicate differing heat stabilities of isoforms of the enzyme, or stabilization of the enzyme by some milk constituent. It is clear that the enzyme can survive, at least partially, processes such as heating at 55 °C for 30 min during manufacture of high-cook cheese varieties (45% survival), and HTST pasteurization (8% survival), and thus may contribute to proteolysis in a range of dairy products.

Type
Original article
Copyright
Proprietors of Journal of Dairy Research 2001

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