According to findings published in Nutrition Research, addition of milk of any kind reduced the antioxidant potential of black tea by between 7 and 25 per cent than unmilked tea.
However, addition of skimmed milk decreased the total antioxidant capacity of black tea much more than whole or semi-skimmed milk, report Lisa Ryan and Sébastien Petit from the Functional Food Center at Oxford Brookes University.
The reduction in the antioxidant activity of tea, as measured by the FRAP assay, was reported to be a linked to the levels of theaflavins and thearubigins that will affect the total antioxidant capacity of black tea.
“Although the addition of milk may not inhibit the catechin or quercetin concentrations, it may affect other antioxidant components such as the theaflavins and thearubigins that will affect the total antioxidant capacity of black tea,” wrote Ryan and Petit.
Green versus black
The majority of science on tea has looked at green tea, with benefits reported for reducing the risk of Alzheimer's and certain cancers, improving cardiovascular and oral health, as well as aiding in weight management.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Considering that the British consume between three and four cups of black tea a day, often with milk (and the rest of the world averages between one and two cups a day), the findings could have public health implications, said the Oxford-based researchers.
“From a public health perspective, tea is rich in antioxidants and may be an important contributor to an individual's overall antioxidant status,” they wrote.
Previous studies have reported somewhat contradictory data. A study from 2007 by German scientists at the Charite Hospital in Berlin found that drinking tea with milk may block the cardiovascular benefits of the catechins.
Writing in the European Heart Journal (2007, Vol. 28, pp. 219-223), the researchers found that while tea increased the artery's ability to relax and expand to accommodate increased blood flow compared to water, this effect was blocked when milk was added to the beverage.
The new research depends our understanding of the potential health benefits of the beverage may be related to the fat content of the milks used, and that not all milk affects the bioavailability of tea compounds equally.
Ryan and Petit analysed the antioxidant capacity of five brands of black with different volumes of whole milk, semiskimmed, and skimmed milk.
Their results showed that adding of 10, 15, and 20 mL of whole, semiskimmed, and skimmed cow’s milk decreased the total antioxidant capacity, but that skimmed milk decreased it the most.
“We accept the hypothesis that different volumes of bovine milk and milk of varying fat content affect the total antioxidant capacity of tea,” wrote Ryan and Petit.
“The degree to which the addition of milk reduces the antioxidant capacity of black tea depends on the amount added and the fat content of the milk,” they added.
And what about coffee?
A recent study by food giant Nestlé reported that adding milk to instant coffee had no effect on the uptake of coffee’s antioxidants, including caffeic acid, ferulic acid, and isoferulic acid.
According to findings of a study with nine people published in The Journal of Nutrition, the uptake of caffeic and ferulic acids was lower, however, when coffee was made with non-dairy creamer and sugar.
The science, testing and regulation surrounding antioxidants will be discussed at the upcoming NutraIngredients Antioxidants 2010 Conference. For more information and to register, please click here.
Source: Nutrition Research
Volume 30, Issue 1, Pages 14-20
"Addition of whole, semiskimmed, and skimmed bovine milk reduces the total antioxidant capacity of black tea"
Authors: Lisa Ryan, Sébastien Petit