Interaction of bovine and caprine milk alpha-caseins with tea polyphenols
Tea (Camellia sinensis) is one of the most commonly consumed beverages. The anticarcinogenic properties of the many phenolic compounds of tea, including catechins, have been shown to inhibit tumor formation in rats. The anticarcinogenic properties of these phenolic compounds have been attributed to their antioxidant activity. However, the antioxidant activity of tea polyphenols may be affected when adding milk to tea. In this work, 7.6 mg/L bovine or caprine milk alpha-casein and 7.7 μM tea polyphenols (catechin, epicatechin, epicatechingallate, epigallocatechingallate, epigallocatechin and theaflavin) were added to an emulsion of linoleic acid (40 mM) prepared using a borate buffer (0.1 M, pH 8.5) and containing 0.1 M of sodium dodecyl sulfate. Interaction of bovine and caprine milk alpha-caseins with tea polyphenols in sodium dodecyl sulfate micelles was studied by a lipid peroxidation method. It was found that the antioxidant activities of the smaller catechins (catechin, epicatechin and epigallotocatechin) were higher in the presence of bovine and caprine milk alpha-caseins. The antioxidant capacity of epigallocatechin was greatly enhanced (P<0.05) by milk alpha-casein (21.3% by bovine milk alpha-casein and 25.2% by caprine milk alpha-casein). The larger and bulkier polyphenols from tea (epicatechingallate, epigallocatechingallate, and theaflavin) did not significantly increase (P<0.05) the lipids protecting effect. These results suggest that bovine and caprine milk alpha-caseins have the potentials to be used as natural ingredients to increase the antioxidant activity of tea polyphenols.
Keywords: bovine and caprine milks, alpha-casein, antioxidant activity, tea polyphenols