Nature's colour scheme
I was walking in North Yorkshire last weekend. The colours of the trees were still amazing, despite some of the heavy weather we have had. The really amazing thing, of course, is that the colour changes in the leaves are purely a result of the degradation of pigments as their nutrients are drained into the branches, trunks and roots for winter storage.
I am researching vegetable pigments at the moment for a science book I'm writing. Some of these pigments are intensely interesting, because they are important to human health. And some just make life a bit more pleasant.
There are four groups of pigments in leaves. These include the chlorophylls, the carotenoids, anthrocyanins and anthoanthins. Pigments in the last two groups tend to be called 'flavanoids.' These include the tannins, such as you find in tea. It is known that they are helpful to us, because they are antioxidants, which oppose some of the harmful chemical reactions that can take place in our tissues as they get older.
The chlorophylls are contained in structures called chloroplasts in the cells of leaves. Their main function is photosynthesis, in which they take in carbon dioxide and water and produce sugars. Green chlorophyll, which makes most leaves green, is the first to degenerate. Another chlorophyll has a red colour, so the leaves start to go orange or brown.
The carotenoids take longer to degrade. These tend to be orange, and are abundant in many of the orange vegetables, such as carrots. Then as the temperature drops the anthrocyanins start to become more dominant and the leaves at the end of the autumn and early winter tend to produce those startling colours that make you want to get out and walk, before the leaves fall completely.
Many of these changes pose real problems in food production, because they tend to make foods look less appetising. Food scientists are forever being challenged in this respect.
Tea is rich in flavanoids. The anthrocyanins give it its colour as you infuse it in the pot or the cup. You may be interested to try out this little experiment next time you prepare tea. Simply pour about an inch of the tea, without milk, into three sturdy glasses. Line them up and check out their even colour. Now, if you add a squeeze of lemon to the first and give it a stir, you will see if turns a much lighter colour. Leave the middle one alone, because that is your comparison. Now add a pinch of sodium bicarbonate to the last. It will darken markedly.
The reason this happens is that anthrocyanins tend to be natural indicators of acidity and alkalinity. The acid of lemon makes the tea go a lighter shade and the alkaline sodium bicarbonate makes it go dark brown. Do not drink the last one, because alkaline tea is not worth drinking!
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Weather for Wakefield
Wednesday 23 May 2012
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Temperature: 13 C to 24 C
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