Tea is the second most consumed beverage in the world after water, and red wine. High polyphenol contents are reported in tea and there is strong evidence that daily intake of foods rich in polyphenols reduces the incidence frequency of diseases due to their antioxidant, anti-inflammatory, and vascular health benefits ffects1. Since tea is consumed in a variety of ways, we will explore in this 3-part article how addition of food components (milk, sweetener, and citrus) can affect antioxidant capacity (ability to scavenge free radicals) and bioavailability (levels absorbed by the body) of polyphenols.

Part I- Should you drink tea with milk?Tea is commonly consumed with the addition of protein-rich milk which is believed to reduce its levels of polyphenol content. The effects of adding milk to antioxidant capacity of tea were discussed in a paper by Ryan and Petit2. Their experiment involves comparison of antioxidant capacity in:1. Teas infused using a teabag and no teabag (infused in leaves).2. Teas brewed after 1, 2, 3, 4, 5, and 10 minutes3. Teas added with cows milk in varying amounts (10, 15, and 20 mL) and varying fat content (whole, semiskimmed, and skimmed). Total antioxidant capacities were measured using a laboratory procedure called modified Ferric iron reducing antioxidant power (FRAP) assay. The teas used in the 3 experiments come in 2.7-3.3 g of tea per tea bag and infused in 200 ml boiling water. All experiments were carried out on a minimum of 3 separate occasions and analyzed in triplicate for each experiment.Findings:

In their first experiment, the antioxidant potential improvedgradually according to the infusion time, with the maximum antioxidant capacity observed in the longest infusion and lowest when brewed for 1 minute. The second part of the experiment compared the antioxidant capacity of teas infused in tea bags from teas infused using tea leaves.

Teas infused in tea leaves results in significantly higher antioxidant capacity. Surprisingly, the maximum antioxidant activity in tea leaves infusion was observed at shorter time (2 minutes ), compared to the tea bag infusion that reached its peak antioxidant capacity 10 minutes.

In the last part of their experiment, water (acting as control), whole milk, semiskimmed milk, or skimmed milk in equal amounts of 10, 15, or 20 mL were added to the tea infusion. The extent at which types of milk affects antioxidant capacity is determined by comparing its values against tea with added water.

For all brands of tea, dilution with any liquid reduces the antioxidant capacity of teas with greatest reduction observed in skimmed milk. The addition of whole milk to each of the teas also decreased the total antioxidant capacity but to a lesser extent.Should we believe this study? A recent review of literature by Ozdal and colleagues examined similar papers that tested the total antioxidant capacity and bioavailability of polyphenols after addition of dairy. However, some studies do not agree due to different methodologies used to measure the antioxidant capacity or total phenolic contents3. Factors such as temperature, pH, types of proteins, protein concentration, types and structures of phenolic compounds may also affect proteinphenolic interactions 3.

Korir et al's paper shows a dose-dependent reduction of antioxidants with addition of milk. However, this can be attributed to increased dilution rather than milk components. Why does milk, particularly skimmed milk appear to reduce antioxidants in tea? This molecular model by Hasni et al4 visually describes how the protein casein, (particularly beta casein) in milk forms a strong complex with tea polyphenols thereby affecting its anti-oxidant capacity. Since skimmed milk has low fat content, much of its component is protein, in a form of casein that has a strong affinity to polyphenols in tea. How about soymilk? Soymilk, derived from soybeans does not contain even a trace of casein. But a study done by Lorenz et al found that adding soymilk to tea appears to reduce its vascular (blood vessel) benefits. They used arterial contraction as measure for vascular benefit and found out that plain tea resulted in more relaxed blood flow. The addition of soymilk is comparable to the hindering effect of cows milk, with more hindering effect observed in milk with added sugar.

Comparing all formulations with plain water (with no benefit), it can be suggested that in terms of health benefits, there might be no sense in drinking tea when combined with interfering foods. They explained that structurally similar soy proteins in soy milk might mimic the effects of caseins in bovine milk in terms of blunting beneficial vascular effects of tea.

Take home message:1)

Part 2- Is sweet tea better?Tea's astringent taste attributed from inherent tannin's interaction with proteins is typically masked by the addition of flavorings and sweeteners. A paper by Sharma5 investigated the effects of milk and sugar in polyphenol content and free-radical scavenging activity of black teas. Their methods however did not mimic the way we normally consume tea that is using tea bags and steeping it in hot water before adding milk and sugar. Rather, tea powder was used combined with milk or tea before brewing.

Plain black tea seems to be highest in antioxidants. Those who want to get fancy with their tea by adding milk or sugar reducing their benefits from drinking tea. Though it wasnt mentioned whether this experiment used whole or skimmed milk, it agrees with the paper discussed above that milk indeed reduces antioxidant activity in teas. Sugar appears to have a reducing effect but at a lower extent. Take note that the addition of both milk and sugar produced a lesser evil than tea with milk alone. This suggests a dose-relationship in reduction of antioxidant with every addition of milk.

A more recent similar study in Africa using tea powders, this time in animals compared the antioxidants in green tea vs. black tea, and the effects of adding stevia, sugar and honey in antioxidant activity of tea6.

First, lets look at green vs. black tea.

There isnt much difference in the antioxidant activity of green (sample1-5) and black teas (sample6-10), so nothing to worry about choosing your tea color. What we should be mindful though is choosing the right sweetener. As shown here, drinking plain tea maximizes its antioxidant benefits. Talking about the right sweetener, Stevia seems to be the perfect choice. Sugar and honey on the other hand can significantly reduce the antioxidants we get from tea in a dose-dependent manner. In fact, adding 10 grams of honey can reduce antioxidants by almost a third and is expected to be further reduced with additional teaspoons. Though the antioxidant activity of honey was, in this study, expected to positively affect the antioxidant activity of tea, it was found to be the most inhibiting sweetener in both plain and black teas with milk. The mechanismby which sucrose inhibits the antioxidant activity in tea is still not fully understood though, as postulated, this may involve the formation of glucosegallic complexes.

Part III.

Another important finding is the time when antioxidant activity reaches its peak. For this mice experiment, blood was drawn after 0, 0.5, 2, 4 and 8 hours in mice fed with green, purple, and black tea (plain and with milk). Glutathione (GSH) levels were measured from blood samples to investigate the effects of the tea bioactive molecules on antioxidant activity. Blood GSH provides evidence on absorption of polyphenols from digestion to blood. Their findings report that antioxidant activity in blood reaches its peak at 2 hours after consumption.antioxidant activity (GSH). Thus, to maximize health effects in the body system, it might be a good idea to replace your liquid intake throughout the day with tea.

Acid and TeaA recent paper by Moser et al suggests that calcium and magnesium can interact with polyphenols to form a metallo-polyphenol complex. So there you have it: a partially complete list of antioxidant-activity reducing components are: milk, sugar, honey, and some minerals. On the other hand, lets look at food component that can help attenuate this interaction.

Using the typical tea preparation in black and green tea, total antioxidant capacity (TAC) was measured by photometric method. They found out that in black tea, anti- oxidant activity increased in a linear manner for the samples containing between 5 and 20 mg ascorbic acid/ 100 ml tea solution (r 14 0:984; p < 0:01). A higher dose of between 25 and 40 mg ascorbic acid/100 ml tea solution of commercially available black and green teas (mmol TE)did not improve the antioxidant capacity of tea. The TAC value decreased at 25 mg ascorbic acid/100 ml to 13.6 mM TE and remained nearly constant to the end of the experiment For green tea (Inter Spar Green Tea in bags), addi- tion of up to 30 mg ascorbic acid/100 ml extract resulted in a linear increase of antioxidant capacity up to 20.8 mmol TE (r 14 0:959; p < 0:01), and it remained un- changed in spite of further vitamin C addition. Black teas contain greater proportions of other polyphenols, such as the theaflavins and thearubigins generated by the oxidative processes used in tea production. These differences in the compositions of teas could be an expla- nation for our results in the experiment with ascorbic acid, in which antioxidant activity of black tea extracts increased up to 20 mg ascorbic acid/100 ml tea solution and of green tea up to 30 mg ascorbic acid/100 ml extract.1) Bourassa, P., Ct, R., Hutchandani, S., & Samson, G. (2013). Journal of Photochemistry and Photobiology B: Biology The effect of milk alpha-casein on the antioxidant activity of tea polyphenols, 128, 4349.2) Ryan, L., & Petit, S. (2010). Addition of whole, semiskimmed, and skimmed bovine milk reduces the total antioxidant capacity of black tea. Nutrition Research (New York, N.Y.), 30(1), 1420. doi:10.1016/j.nutres.2009.11.0053) Ozdal, T., Capanoglu, E., & Altay, F. (2013). A review on protein phenolic interactions and associated changes, 51, 954970.4) Hasni, I., Bourassa, P., Hamdani, S., Samson, G., Carpentier, R., & Tajmir-Riahi, H.-A. (2011). Interaction of milk - and -caseins with tea polyphenols. Food Chemistry, 126(2), 630639. doi:10.1016/j.foodchem.2010.11.0875) Sharma, V., Vijay Kumar, H., & Jagan Mohan Rao, L. (2008). Influence of milk and sugar on antioxidant potential of black tea. Food Research International, 41(2), 124129. doi:10.1016/j.foodres.2007.10.0096) Korir, M. W., Wachira, F. N., Wanyoko, J. K., Ngure, R. M., & Khalid, R. (2014). The fortification of tea with sweeteners and milk and its effect on in vitro antioxidant potential of tea product and glutathione levels in an animal model, 145, 145153.7) Lorenz, M., Stangl, K., & Stangl, V. (2009). Vascular effects of tea are suppressed by soy milk. Atherosclerosis, 206(1), 312. doi:10.1016/j.atherosclerosis.2009.02.0018) Moser, S., Chegeni, M., Jones, O. G., Liceaga, A., & Ferruzzi, M. G. (2014). The effect of milk proteins on the bioaccessibility of green tea fl avan-3-ols, 66, 297305.9) Majchrzak, D., Mitter, S., & Elmadfa, I. (2004). The effect of ascorbic acid on total antioxidant activity of black and green teas. Food Chemistry, 88(3), 447451. doi:10.1016/j.foodchem.2004.01.058