Antioxidant nature of bovine milk beta-lactoglobulin.
Heating is necessary for processing milk in the dairy industry, which evidently produces a conformational change in beta-lactoglobulin (beta-LG). beta-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 beta-LG in milk and the possible mechanism involved. We showed that beta-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 beta-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 beta-LG by heating (100 degrees C for 2 min), or chemically modifying the beta-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 beta-LG. By using an anti-LG antibody affinity column to deplete the beta-LG from milk, we observed from the lost antioxidant activity that beta-LG contributes approximately 50% of the total activity. Because beta-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.
Liu
H C
HC
Department of Biological Science and Technology, College of Biological Science and Technology, National Chiao Tung University, Taiwan, Republic of China.
Chen
W L
WL
Mao
S J T
SJ
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D015153:Blotting, Western; D002417:Cattle; D003432:Cross-Linking Reagents; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005511:Food Handling / Q000379:methods; D006358:Hot Temperature; D007782:Lactoglobulins / Q000737:chemistry / Q000494:pharmacology*; D008892:Milk / Q000737:chemistry*; D011489:Protein Denaturation; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000737:chemistry
D000975:Antioxidants; D003432:Cross-Linking Reagents; D007782:Lactoglobulins; D013438:Sulfhydryl Compounds