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Lactoperoxidase-induced protein oxidation in milk
H Ostdal1, M J Bjerrum, J A Pedersen
1Department of Animal Product Quality, Danish Institute of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark. Henrik.Ostdal@agrsci.dk
Journal of Agricultural and Food Chemistry
|September 20, 2000
Summary
Lactoperoxidase (LPO) and hydrogen peroxide (H2O2) generate protein radicals and dityrosine. BSA and beta-lactoglobulin stabilize these radicals, while casein increases dityrosine formation in milk.
Area of Science:
- Biochemistry
- Enzymology
- Oxidative Stress
Background:
- Lactoperoxidase (LPO) is an enzyme found in milk.
- Hydrogen peroxide (H2O2) is a key substrate for LPO activity.
- Protein oxidation can lead to the formation of radicals and dityrosine.
Purpose of the Study:
- To investigate the formation of protein radicals and dityrosine by LPO and H2O2.
- To examine the influence of milk proteins (BSA, beta-lactoglobulin, casein) on this reaction.
- To assess LPO activity in both unpasteurized and UHT milk.
Main Methods:
- Freeze-quench electron spin resonance (ESR) spectroscopy to detect protein radicals.
- Measurement of dityrosine as a marker of protein oxidation.
- Incubation experiments at 25°C with varying reaction components.
- Analysis of endogenous LPO activity in milk.
Main Results:
- BSA and beta-lactoglobulin formed long-lived protein radicals detectable by ESR.
- Casein increased dityrosine formation compared to LPO and H2O2 alone.
- Radical species and dityrosine were detected in unpasteurized milk and UHT milk supplemented with LPO and H2O2.
Conclusions:
- LPO and H2O2 generate ESR-detectable radicals and dityrosine, with varying effects from different milk proteins.
- LPO plays a crucial role in radical and dityrosine formation in milk.
- This enzymatic system contributes to oxidative modifications in milk.