Valuable antioxidants in coffee and tea

At some time late last century, coffee preferences split into a score of variants. The sound of baristas drumming out their used beans now reverberates through the CBDs. More recently, ‘old gumboot’ tea evolved into the new urban sophisticate – and a wide variety of exotic and herbal teas have become de rigueur in educated health-conscious circles. We are increasingly fussy about our beverages, but what do we actually know about the benefits or harm caused by tea and coffee drinking.

It was a well-known fact in 1960’s grandmotherly circles that you should not drink tea with your meals because compounds in the tea would bind with the iron in food, preventing their absorption. Dr Ali Rashidinejad, a food scientist at the Riddet Institute (Massey University), who has spent years researching the ‘bioactive’ compounds in food and drink, especially teas and coffees, confirms this wisdom

However, all coffees and teas, notably green tea, contain valuable antioxidants which counteract the destructive effects of the free radicals responsible for many chronic diseases, and have a protective effect against various diseases such as Alzheimer’s (now we have your attention!).  Take that as a licence to continue your habit, in moderation.

Dr Rashidinejad suggests an at-home experiment to show the existence of these antioxidants.  Make a cup of black or green tea, pour it into a glass and leave it.  Note the change of colour.  Green tea goes red or even black, given enough time. This is due to the action of an enzyme that progressively breaks down some of the polyphenolic antioxidants, reducing their potency.  Don’t let your tea draw for longer than 8 minutes if you want to get the most out of your brew.

Another factor affecting the degree of bioactive benefit is temperature.  Ali advises that you are better to make tea and coffee with water below boiling point.  A lot of bioactives are not stable under very hot conditions.

And the quality of tea counts, not just with taste. The bioactive content depends on several factors – ages of the leaf, the season when it is harvested, and the way the tea is dried, fermented, and stored.

Ali himself is a big consumer of green tea, which is not only rich in antioxidants, but has a lot less caffeine than coffee or black tea. One question that has consumed him for the last decade is the effect of adding milk to tea and coffee.  Does the milk change or reduce the uptake of bioactives? Of course milk has its own nutritional benefits, but is it better to consume your dairy separately, and drink your tea and coffee black?

The results of research by Ali and others, although showing a mostly negative effect of milk addition on the bioactivity of both tea and coffee, is not black and white and is unlikely to influence drinking habits. What is becoming increasingly clear, too, is that digestion and the uptake of nutrients from food and drink vary a lot among individuals. But it is safe to generalise about the immeasurable social benefits of getting together over a cup of coffee or tea.


This article is reproduced from Stuff that originally appeared on 26th July 2021. Article by Dr Ali Rashidinejad and science writer Glenda Lewis.

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