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We've been reading a lot in magazines and newspapers about antioxidant plant foods, including berries like blueberries and cranberries, and we keep seeing the word anthocyanins.

What are anthocyanins?

Anthocyanins (Etymology: Greek. anthos = Flower, ky'neos = purple) are water-soluble pigments reflecting the red to blue range of the visible spectrum. The colour depends on the acidity of the surrounding medium.

Anthocyanins exist only in plants with bright colors in everything from flower petals to autumn leaves and edible fruits or vegetables. Chemical identification studies reveal that there are as many as 600 unique anthocyanins in nature.

How are anthocyanins synthesized in the plant?

Here's a brief botany summary. Anthocyanins are formed from chemical raw materials in the plant, using the amino acid phenylalanine, or another chemical called malonyl coenzyme A. These two substrates join to form the base material for anthocyanins called 'chalcones' that lead to the production of anthocyanins after a series of enzyme steps.

The parent material of anthocyanins is a group of similar structures named 'anthocyanidins' or 'proanthocyanidins' which contain no sugar molecules. When sugars become attached, an anthocyanin glycoside is formed, taking the characteristic shape of anthocyanins.

When first isolated by chemists, many anthocyanins were named after the colorful flowers from which they were extracted, such as petunidin (petunia), rosinidin (rose) and peonidin (peonies).

The large class of antioxidant cyanidins is also anthocyanins ' all these compounds belong to the group of compounds called flavonoids within the super-family of antioxidants named phenolics or polyphenols.

What is the purpose of anthocyanins in a plant?

Anthocyanins exist mainly to preserve the regeneration of the plant. In flowers, the colorful anthocyanins of petals attract pollinators whereas in fruits, like brightly colored berries, they reside in the skin to attract animals that eat the fruit and later disperse the seeds in their droppings. This is nature's efficient way of symbiosis between a plant and feeding animal.

Anthocyanins also serve a protective role much like a 'sunscreen' by absorbing the ultraviolet light that plants face from constant sun exposure.

This "sunscreen" function is thought to be the reason why many deciduous plants turn red in autumn. When green chlorophylls break down, and as leaves begin to dehydrate and die, anthocyanins shield the remaining leaf tissues while the plant moves nutrients back into the stems and vascular system of the tree.

How do people benefit from anthocyanins and what plant foods contain them?

In berry research particularly, anthocyanins have been shown to possess strong antioxidant qualities that guard cells of the fruit pulp and seeds from reactive oxygen species ('free radicals') formed during normal plant metabolism and exposure to ultraviolet light.

When people eat anthocyanin-rich foods, we obtain the benefit of these antioxidant qualities, giving us the same capacity for combating the damaging free radicals.

Among plant foods providing the richest sources of anthocyanins are blueberries, cranberries, blackberries, red currants and cherries (up to 400 mg in every 100 gram serving) and Concord grapes (as high as 750 mg/100 grams). Two of the richest sources of anthocyanins in berries are in the black raspberry and tropical palmberry (or acai).

A good rule of thumb is this: dark blue, purple or black fruits that easily stain your fingers (or thumb) during picking are great sources of anthocyanins.

Non-berry plant foods rich in anthocyanins include brightly colored (bluish) vegetables like the purple cabbage and eggplant. White plant foods like banana, pear and potato do not contain significant levels of anthocyanins.

Are there known health values of eating anthocyanin-rich foods?

Medical research has been examining potential health or anti-disease benefits of having anthocyanin-enriched plant foods like berries included in the regular human diet.

Although the work must be considered preliminary until thorough clinical trials are completed, the list of potential benefits are many and includes positive effects against:

' Cancer
' Diabetes
' Inflammation
' Heart and vascular disease
' Alzheimer's disease
' Other types of neurodegeneration
' High blood cholesterol
' Stroke
' Bacterial infections
' Urinary tract infections
' Age-related eyesight deterioration
' Premature aging

Reading

Wikipedia, free encyclopedia, http://www.wikipedia.com

PubMed, online literature database of the US National Library of Medicine, http://pubmed.gov

Shahidi F, Naczk M. Phenolics in Food and Nutraceuticals, CRC Press, Boca Raton, 2003.