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Antioxidant Nature of Bovine Milk ß-Lactoglobulin

H. C. Liu^*, W. L. Chen^* and S. J. T. Mao^*,1

^* Department of Biological Science and Technology, College of Biological Science and Technology, National Chiao Tung University, Taiwan, Republic of China
^* Department of Biotechnology and Bioinformatics, Asia University, Taichun, Taiwan, Republic of China

¹ Corresponding author: mao1010{at}ms7.hinet.net

Heating is necessary for processing milk in the dairy industry, which evidently produces a conformational change in ß-lactoglobulin (ß-LG). ß-Lactoglobulin, a major protein that accounts for approximately 10 to 15% of total milk proteins, is a globular protein consisting of 162 AA with a relative molecular mass of 18.4 kDa. The purpose of the present study was to determine the antioxidant role of ß-LG in milk and the possible mechanism involved. We showed that ß-LG is a mild antioxidant whose potency is less than that of vitamin E and probucol (the latter being an antioxidant used for clinical therapy). The conversion of the ß-LG monomer to dimer was responsible, in part, for the mode of action in protecting low-density lipoproteins against copper-induced oxidation. Cross-linking the free thiol groups of ß-LG by heating (100°C for 2 min), or chemically modifying the ß-LG by carboxymethylation to block the thiol groups resulted in a substantial loss of antioxidant activity. The data suggest that Cys-121 plays an essential role in the antioxidant nature of ß-LG. By using an anti-LG antibody affinity column to deplete the ß-LG from milk, we observed from the lost antioxidant activity that ß-LG contributes approximately 50% of the total activity. Because ß-LG is extremely sensitive to thermal denaturation, to maintain its antioxidant nature, dairy products consumed daily should not be overheated in order to maintain its antioxidant nature.

Key Words: ß-lactoglobulin • antioxidant activity • mechanism • milk