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Color pigments in plants: carotenoids, flavonoids, betalains, chlorophylls

14 Jun 2013, 19:57
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You may have recently noticed all the new vegetables in new sometimes crazy colors appearing in the local supermarkets or your farmer's market. Things like purple broccoli or red onions may not just look awesome but also appear to pack something extra nutritionally.

purple cauliflower and beets

Of course, consumers have always been interested in the new unusual products. Everything that is at least a little bit different draws attention of most humans right away. It is probably one of the reasons why you see pink cabbage or red cucumbers on the shelves. But there are others reasons, much more interesting.

 

The information from the recent scientific studies shows that plants' pigments can be very beneficial for human health. Plants produce these chemicals for their own purposes, but when we eat bright pigment-containing foods we can successfully utilize them for our own metabolism as well.

different colors of carrots

 

Pigments are naturally occurring. Say, for example, carrots. We are used that they are orange, but initially carrots were either light yellow or purple. After the first carrots had been found in early 1600's, through next hundreds of years of selection only the better looking and tastier orange carrots were left widely spread.

 

Plants, as all other living creatures, go through naturally occurring chaotic mutations that may lead to changes in hue and pigments' saturation. Then people notice it, and boom, we have completely different looking food.

 

In this way original orange cauliflower was accidentally found in Holland in the growing field. It has exactly the same beta-carotene that carrots have, so it proves to be much more beneficial in terms of nutritional value.

powders of pigments

 

All the major pigments can be broken down into four categories.

 

Pigment

Common types

Where they are found

Examples of typical colors

 

Betalains

 

 Betacyanins and betaxanthins

 

Flowers and fungi

 

Red to violet, also yellow to orange

Carotenoids

    

     Carotenes and

xanthophylls (e.g. astaxanthin)

 

 

Bacteria. Green plants (masked by chlorophyll), vegetables like carrots, mangoes and so on. Some birds, fish and crustaceans absorb them through their diets

Oranges, reds, yellows, pinks

Flavonoids

 

Anthocyanins, aurones, chalcones, flavonols and proanthocyanidins

 

 

Produce many colors in flowers. Common in plants such as berries, eggplant, and citrus fruits. Present in certain teas, wine, and chocolate

Yellow, red, blue, purple

 

Chlorophylls

 

Chlorophyll

 

Green plants

 

Green

 

Betalains

 

Like carotenoids and flavonoids, betalains also seem to play an important role in attracting animals to flowers and fruit, and produce a similar range of colors. The betalains consist of two sub-groups, red-violet (betacyanin) and yellow to orange (betaxanthin) pigments. They only occur in a few plant families, and always independently of anthocyanins.

 

Betacyanins are established food colorants. Betalains give rise to the distinctive deep red of beetroot. The composition of different betalain pigments can vary, giving rise to breeds of beetroot that are yellow or other colors, in addition to the familiar deep red.

 

The betalains in beets include betanin, isobetanin, probetanin, and neobetanin (the red to violet ones are known collectively as betacyanin). Other pigments contained in beet are indicaxanthin and vulgaxanthins (yellow to orange pigments known as betaxanthins). Betalains cause the crimson of Amaranthus flowers (class of Caryophylalles).
 

Carotenoids

 

Carotene is a pigment that absorbs blue and indigo light, and that provides rich yellows and oranges. The distinctive colors of mango, carrots, fall leaves, and yams are due to various forms of carotene, as is the yellow of butter and other animal fats. This pigment is important to our diet, as the human body breaks down each carotene molecule to produce two vitamin A molecules.
 

Lycopene, canthaxanthin, and astaxanthin share a similar structure to carotene. The red tones of tomatoes, guava, red grapefruit, papaya, rosehips, and watermelon indicate the presence of lycopene.

 

Canthaxanthin produces the pink colors of flamingos, some crustaceans, salmon, and trout. In its synthetic form, it is used to ensure captive flamingos retain their coloring, as a red food colorant, and even as a tanning aid. Astaxanthin provides the red colors of cooked salmon, red bream, trout, lobster, and shellfish. In a live animal, astaxanthin is combined with a protein and is blackish in color. When boiled, the protein breaks down to unmask the true “lobster red” of astaxanthin.

 

Flavonoids

 

Flavonoids are the yellow plant pigments seen most notably in lemons, oranges, and grapefruit. The name stems from the Latin word "flavus," which means yellow. Flavonoids in flowers and fruit provide visual cues for animal pollinators and seed dispersers to locate their targets. Flavonoids are located in the cytoplasm and plastids. Many of the foods that we eat, including dark chocolate, strawberries, blueberries, cinnamon, pecans, walnuts, grapes, and cabbage, contain flavonoids.

 

These chemicals lower cholesterol levels, and many have antioxidant properties. Anthocyanins and proanthocyanidins, and the reddish-brown pigment theaflavin found in tea, act to create color, while most other flavonoids are visible only under UV light.
 

Anthocyanins play a role in the colors of ripening fruit. They are found in most other plant parts and in most genera. Anthocyanin pigments take their color from the range of red, purple, or blue, depending on their pH.

 

Blueberries, cranberries, and bilberries are rich in anthocyanins, as are the berries of the Rubus genus (including black raspberry, red raspberry and blackberry), blackcurrants, cherries, eggplant peel, black rice, Concord and muscadine grapes, red cabbage, and violet petals. Anthocyanins are partly responsible for the red and purple colors of some olives.
 

Proanthocyanidins are linked to the beige color of the broad bean seed coat, and also to shades of black, red, brown, and tan. Apples, pine bark, cinnamon, grape seed, cocoa, grape skin, and the grapes used to make most red wines all contain proanthcyanidin.

 

The yellow colors of flavonoid pigments can be found as chalcones (found in flowers and the organs of plants), aurones (found in flowers and some bark, wood, or leaves) and flavonols.

 

The betalains in beets include betanin, isobetanin, probetanin, and neobetanin (the red to violet ones are known collectively as betacyanin). Other pigments contained in beet are indicaxanthin and vulgaxanthins (yellow to orange pigments known as betaxanthins). Betalains cause the crimson of Amaranthus flowers (class of Caryophylalles).

 

Chlorophylls

 

Chlorophyll is green, and is responsible for the green color of foliage and leaves. More importantly, by enabling plants to produce oxygen during photosynthesis, it is critical to sustaining our life on earth. Chlorophyll has structural features similar to heme. Bilirubin, which produces a yellow color, has recently been found in plants.

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