Since theaflavin now exists as a [casein-theaflavin] complex, it loses the antioxidant properties it once posesses... the antioxidant potential of the tea after milk has been added is roughly 80% of it's original."The scientific study that tb cites focuses mainly on the polyphenols found in green tea, analyzing the masking of many individual polyphenols that are abundant in green tea and not so abundant in black tea. It does so for both green and black teas, and gives proportions for how each polyphenol accounts for the total antioxidant masking in both teas (see Figure 5 in the PDF). Accordingly, theaflavin only accounts for 0.6% of the total antioxidant masking, whereas tb considers theaflavin to be the main culprit involved. The source article does not however analyze thearubigin, and I assume this falls under the "unknown" category in this study. In fact, 85% of what contributes to the masking that beta-casein provides is in the "Unknown" category. What is the antioxidant that is masked by milk proteins? The study speculates:
Probably tannins, polymers of oxidized polyphenols (9), have a significant contribution to the antioxidant capacity of black tea."Could it be thearubigin? The study specifically mentions polymers as contributing to the antioxidant capacity of black tea. This likeliness that it is thearubigin is confirmed by another study, which says: "The major fractions of black tea polyphenols, accounting for >20% of the solids in brewed black tea, are known as thearubigens."
But how thearubigen and its polymer chain reacts with milk proteins, we do not know. According to tb, the thearubigin polymer chains that are almost instantly formed when released into hot water are stable enough that they will not react with the compounds in milk. Is this true? And if so, which antioxidants account for the majority of the masking done by milk proteins?
More questions to answer, the search for tea knowledge continues!! Time to ponder and enjoy a good cup of green tea :)