Flavonoids

Flavonoids are a large family of secondary compounds synthesized by plants and collectively known as Vitamin P or citrin. Preliminary research indicates that flavonoids may modify allergens, viruses, and carcinogens, and so may be biological "response modifiers".

Flavonoids are classified into subclasses, depending on their chemical structure,. More than 4000 flavonoids have been identified, and they are among the most potent and abundant antioxidants in our diet as important components of many fruits and vegetables.

They have become popular for all the many health promoting effects. Some of these include: Anti-cancer, anti-allergic, antioxidant, anti-inflammatory and anti-viral capabilities.

Some important subclasses are:

1. Flavonols
   • Quercetin (in onions, capers, apples, broccoli, cranberries, citrus fruits, tomato, broccoli)
   • Myricetin (in berries, grapes, parsley, spinach, walnuts)
   • Kaempferol (in broccoli, grapefruit, brussel sprouts, apples)
2. Flavones
   • Luteolin (in beets, bell peppers, brussels sprouts, cabbage, cauliflower, celery, hot peppers, lettuces, spinach, thyme)
   • Apigenin (in celery, lettuce, parsley)
3. Flavanones
   • Hesperetin (in citrus fruits and juices)
   • Naringenin (in grapefruit, oranges, tomato skin)
4. Flavan-3-ols (flavanols)
   • Catechin (in tea, red wine, cocoa powder, dark chocolate, grapes, plums)
   • Epicatechins (variety of teas, fruits, legumes)
5. Anthocyanidins
   • Cyanidin (in bilberry, blackberry, blueberry, cherry, cranberry, raspberry, apples, pears, peaches, plums), the highest concentration are found in the skin of the fruit.
   • Delphinidin (in cranberries, concord grapes, pomegranates)
   • Malvidin (red grapes, cranberries, blueberries and black rice)
   • Pelargonidin (raspberries, strawberries, blueberries, cranberries, pomegranates, plum)

The widespread distribution of flavonoids, their variety and their relatively low toxicity compared to other active plant compounds (for instance alkaloids) mean that many animals, including humans, ingest significant quantities in their diet.

Flavonoids have been referred to as "nature's biological response modifiers" because of strong experimental evidence of their inherent ability to modify the body's reaction to allergens, viruses, and carcinogens. They show anti-allergic, anti-inflammatory, anti-microbial and anti-cancer activity.

Consumers and food manufacturers have become interested in flavonoids for their possible medicinal properties, especially their putative role in prevention of cancers and cardiovascular diseases. Although physiological evidence is not yet established, the beneficial effects of fruit, vegetables, and tea or even red wine have been attributed to flavonoid compounds rather than to known nutrients and vitamins.

UCLA cancer researchers have found that study participants who ate foods containing certain flavonoids seemed to be protected from developing lung cancer. Dr. Zuo-Feng Zhang, of the UCLA's Jonsson Cancer Center and a professor of public health and epidemiology at the UCLA School of Public Health said the flavonoids that appeared to be the most protective included catechin, found in strawberries and green and black teas; kaempferol, found in brussel sprouts and apples; and quercetin, found in beans, onions and apples.

References:

• Isoflavonoids and neoflavonoids; IUPAC Compendium of Chemical Terminology.
• Flavonoids: modulators of brain function?; The British journal of nutrition.
• Antimicrobial activity of flavonoids; International Journal of Antimicrobial Agents.
• Fruits, vegetables, teas may protect smokers from lung cancer; UCLA news May 2008.
• Phytochemical Information Center; PBH. USDA Database of Flavonoid content of food.
• Fruit Value & Nutritional Facts; Jay-Amms Fruit Stores.