Of course there are numerous plant pigments. I will not even try to be exhaustive on the subject, but will concentrate on three categories. One is chlorophyll, unavoidable when discussing plants and colours. The two others are of interest not only for plant-life itself, but also for human nutrition: bioflavonoids and carotenoids. It should be added, however, that all colours are not pigments. The white of flowers, for instance, is mostly caused by scattering, where the particles are large enough to reflect all light
A flower or a fruit always contains many pigments. Its appearance is sometimes dependent on which pigment that is the dominant one, and sometimes it is a result of mixing colours. So do not be surprised to read that apples contain blue-violet-red pigments, or that all green leaves contain carotenoids (yellow-orange-red pigments).
Hundreds of carotenoids and bioflavonoids are known to science, many of them specific for a certain species. Except for some special cases, it is of no real interest to discuss distinct pigments separately, they can more appropriately be treated as subgroups. (Carotenoids were discussed in a previous article, Not Only Beta-Carotene: Carotenoids (Carotenes & Xanthophylls), and will only briefly be mentioned here.)
As for bioflavonoids, a common standard of terms and of a classification into subgroups are still lacking. There is not even a universally accepted definition of "bioflavonoids". I have chosen here to use it as a collective name of water-soluble pigments of flowers and fruits, of which at least some variant has some nutritional interest for humans. This definition might be lacking in scientific stringency, but will suffice for this context.
The breakdown of bioflavonoids into subgroups will be made only to make the subject more readily understandable, without any ambition to scientific correctness.
While the bioflavonoids are water-soluble, the carotenoids are fat soluble, something which makes the distinction simple. It also means that when we desire these pigments for their nutritional or medical value, carotenoids must be ingested with some fat, lest we cannot absorb them. Absorption of bioflavonoids, however, requires just some accompanying water.
Pigments - Chlorophyll
No doubt, chlorophyll is the most striking colouring matter of nature, because of the sheer visible amount of it. It is the green colouring matter of plants. In the presence of sunlight it converts carbon dioxide and water to carbohydrates.
It is sometimes used as a dye and in medicine, where some claims about its beneficial effects have been made, but remain so far unproved. One of the most common claims is that it would eliminate offensive odours.
Chlorophyll is a very strong pigment, we can call it dominant. All green parts of plants contain many other pigments as well, but we cannot see them. They are concealed by the chlorophyll.
How did it begin? Very long ago, Mother Earth had an atmosphere containing no free oxygen. The single-celled organisms which dominated then, produced energy from fermentation and glycolysis. A cyanobacterium, a single-celled organism, developed the chlorophyll and the photosynthesis. This organism then penetrated another cell, and established itself as an endosymbiont. [A symbiont is an organism living in a symbiotic relationship with another. An endosymbiont lives within the other party.] Obviously it was evolutionary successful, from this symbiosis descends all or almost all photosynthetic cells. The endosymbiont became what we today call a chloroplast, an organelle living in every cell of all photosynthetic plants, where it manages the photosynthesis.
The chloroplasts do not only contain the chlorophyll, but carotenoids too. The latter absorb blue light and add to the photosynthetic process - and they protect the plant against sun-induced oxidation
Pigments - Bioflavonoids
Anthocyanins (sometimes divided into Anthocyanidins and Proanthocyanidins) are pigments mainly found in certain flowers, fruit and vegetables with red-blue colours. Good sources are for example: blueberries/bilberries, red cabbage, eggplant, radishes, tea, beets, cherries, plums, red grapes, hawthorn, apple, pear, grape seed, pine bark, beer, red wine, cranberry, red beans and some other berries. This is also what gives roses their colour.
Other flowers with anthocyanins are geranium and Dahlia (with pelargonidin); bluebottle and some asters (with cyanidin); larkspur, violet and pansy (with delphinin).
Medically these substances are strong antioxidants, even very strong. They also decrease capillary weakness, and support vitamin C activity. Good effect on eyes. Strong anti-inflammatory and anti-allergic properties.
Betalains, red-yellow pigments. Chemically related to anthocyanins, they are found only in Caryphyllales. A good dietary source is reed beet.
Citrus bioflavonoids are mainly yellow pigments enhancing the effect of vitamin C and protecting it against oxidation. They are antioxidants in themselves as well. They are preserving and repairing the structure of the capillaries (small blood vessels), protect against heart disease; they are antibacterial and they seem to protect against cataract. They have clear antibacterial, antiviral and anti-inflammatory properties. Can be used against any sort of varicose veins. Studies have shown excellent results in that respect.
The most well-known and researched citrus bioflavonoids are: Rutin, Hesperidin, Quercitrin and Tangeritin.
Good sources: Citrus, especially the pith just below the peel, peppers, grapes, pine bark, onions, garlic, blue and red berries, green tea and buckwheat.
Quercetin is chemically related to proanthocyanins and it is the most active of the known flavonoids. It is the active substance in many medical plants and has proved to have a very strong anti-inflammatory and anti-viral effect. Quercetin has been studied in connection with cancer treatment, but the result is not so clear. Some studies show that it can possibly, under certain circumstances, be a contributory factor in causing cancer. But that is still quite unclear.
Catechin is a pigment of cocoa. (Also present in green tea, see below.) Studies indicate that it protects against heart disease and cancer. The beneficial effect does not apply to chocolate. The reason for this is the many undesirable ingredients that it contains in addition to cocoa.
Cocoa should not be used in excess, because it also contains theobromine, which can be toxic. For a dog or a horse it is deadly. Never give them chocolate!
Green tea polyphenols are best derived from tea plant Camellia sinensis. It has a very strong antioxidative effect, and it is good for cancer prevention in that it suppresses the activity of carcinogens [compounds causing cancer].
One of the polyphenols in green tea is catechin (see above).
Pigments - Carotenoids
See Not Only Beta-Carotene: Carotenoids (Carotenes & Xanthophylls).
Saffron and Turmeric
Saffron provides not only the spice of that name, not only several medical effects, but it also has been used for dyeing fabrics. Ladies of nobility of the Antiquity often wore yellow robes, dyed with saffron. It was a sign of high station.
The colour of saffron is a combination of several medically active carotenoids: alpha- and beta-carotene, zeaxanthin and lycopene. Breakdown of zeaxanthin gives safronal and pirocrocin, which cause the typical taste and aroma of the spice.
Crocin, a carotenoid contributing the colour of saffron is a strong neuro-protector.
Curcumin, the colour of turmeric, does not only provide a beautiful golden-yellow colour, it is a potent medical drug too. The health benefits of turmeric are indeed astonishing, almost beyond competition. Most of them undoubtedly a result of curcumin, but it is impossible to say to what extent other compounds in turmeric contributes.
Obviously curcumin reaches the cell membranes, where it has a key role in keeping them in good shape and thus the cells themselves healthy.
For more on the health benefits of turmeric, see: The King & Queen of Spices: Turmeric & Ginger
...and for the health benefits of saffron, see: The Three Most Expensive Spices.
Previous articles in the series on colours:
Colours I : The Nature of Colour 1
Colours II : The Nature of Colour 2
Colours III: Function, Purpose, & Effect of Colour
Colours IV: Colours of Animals
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(The lead image shows vegetation being green by chlorophyll. Photo by Mylene2401/Pixabay, CC0/Public Domain. The image has been digitally enhanced.)
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