Flavonoids are a group of plant pigments with many functions. They act as cell wall support materials and as colorful attractants for birds and insects helping seed dispersal and pollination.

Flavonoids exert antioxidant acitivity that is generally more potent and effective than traditional antioxidant nutrients vitamin C and E, beta-carotene, selenium, and zinc. Flavonoids are sometimes called "nature's biological response modifiers" because of their anti-inflammatory, antiallergenic, antiviral, and anticancer properties.

Flavonoids, particularly flavan-3-ols and proanthocyanidins, have been associated with reduction in the risk of cardiovascular disease by increasing the release of endothelial nitric oxide (NO) and preventing narrowing of the blood vessels. Anthocyanidins may also decrease cholesterol oxidation through their high antioxidant activity. Proanthocyanidins (PAs), the polymers of flavan-3-ols, also referred to as condensed tannins, are known for contributing astringent flavor to foods. Recently it has been suggested that the free radical scavenging properties of PAs may reduce the risk of cancer, blood clotting and certain types of trimeric PAs may protect against urinary tract infections. Flavonoids are also able to chelate (bind) metals, stimulate the immune system and also reduce an allergic response, and protect against bacteria and viruses.

Major Flavonoid Classes

Flavonoids fit into several subclasses:

Seven classes of flavonoids common in foods are usually considered for their medicinal properties:

  1. Anthocyanidins
  2. Proanthocyanidins
  3. Flavones
  4. Flavonols
  5. Flavan-3-ols
  6. Flavanones
  7. Isoflavones


Pelargonidin, cyanidin, delphinidin, peonidin, petunidin, malvidin, apigeninidin, luteolinidin, tricetinidin, aurantinidin, 6-hydroxy-cyanidin, 6-hydroxy-delphinidin, rosinidin, hirsutidin, 5-methyl-cyanidin, pulchellidin, europinidin, capensinidin. Anthocyanidins increase vitamin C levels within cells, decrease the breakage of small blood vessels, protect against free-radical damage, and help prevent destruction of collagen thus promoting healthy skin and connective tissue. The anthocyanidins are most abundant in fruits and red wine and less frequent in vegetables. Best food sources: blueberries, blackberries, plums, cranberries, raspberries, red onions, red potatoes, red radishes, and strawberries.

Dark grapes are rich in flavonoids


Monomers, dimers, trimers, 4-6 mers (tetramers, pentamers and hexamers), 7-10 mers (heptamers, octamers, nonamers and decamers), polymers (DP>10). This group of polymers, if broken apart with acid treatment, yield anthocyanidins such as cyanidin. Proanthocyanidins are sometimes referred to as condensed tannins and are responsible for astringency in many foods and medicinal herbs. Proanthocyanidins have strong antioxidant properties and may reduce the risk of cardiovascular disease and cancer. Some proanthocyanidins may protect against urinary tract infections. The growth of certain pathogenic bacteria such as Clostridium perfringens, C. difficile and Bacteroides species was significantly inhibited by tea phenolics. Best sources: tea, cocoa, many berries, grape juice, cranberries, and red wine.


Apigenin, luteolin, tangeretin, nobiletin. Apigenin has chemopreventive properties. Luteolin has been shown in animal studies to have anti-cancer, anti-inflammatory, anti-allergic effects, and anti-asthma effects. Tangeretin and nobiletin, citrus polymethoxylated flavones found in the peel of citrus fruits exhibit anti-proliferative, anti-invasive, anti-metastatic, and antioxidant activities. They also have the potential to reduce blood pressure and plasma glucose levels. Apigenin: celery, lettuce, parsley. Luteolin: beets, bell peppers, Brussels sprouts, cabbage, cauliflower, celery, hot peppers, lettuces, spinach, thyme. Tangeretin & nobiletin: peel of citrus fruits; shekwasha (citrus fruit).

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myricetin, quercetin, isorhamnetin, kaempferol, isorhamnetin. Myricetin has anti-inflammatory and anti-cancer effects. Quercetin, the main flavonoid in the diet, may lower risk for asthma, heart disease, and lung cancer. Best sources for myricetin: berries, grapes, parsley, spinach. Best sources for quercetin: onions, apples, broccoli, cranberries, grapes.


Catechins and gallic acid esters of catechins, epicatechins and gallic acid esters of epicatechins, theaflavins and gallic acid esters of theaflavins, thearubigins. Catechins and epicatechins may lower the risk of coronary heart disease, some types of cancers and promote healthy lungs. Best sources for catechins: tea, red wine, cocoa powder, dark chocolate, grapes, plums. Best sources for epicatechins: teas, fruits and legumes (beans).


Hesperetin, naringenin, eriodictyol. Hesperetin found in grapefruits and oranges is one candidate that may benefit the cardiovascular system (atherothrombotic diseases, and lower the levels of LDL cholesterol. Naringenin has antioxidant, anti-estrogen, and cholesterol-lowering properties. Best sources for hesperetin: citrus fruits and juices. Best sources for naringenin: citrus fruits and juices. Naringenin and quercetin are the most active with the lowest minimum inhibitory concentrations for all of the four bacteria tested (Lactobacillus rhamnosus, E. coli, Staphylococcus aureus and S. typhimurium, and H. pylori ).


Daidzein, genistein. Isoflavonoids (also called isoflavones) have been suggested to have strong antioxidative properties. Best sources: soya, soya products, red clover.

Anticancer Properties of Anthocyanins

Anthocyanins are a group of naturally occurring phenolic compounds present in many berries, dark grapes, cabbages and other pigmented foods. Epidemiological studies show that a moderate consumption of complex mixtures of anthocyanins, such as red wine or bilberry extract, is related to the low risk of cardiovascular disease. Mixtures of anthocyanins (such as in plant extract) have also been shown to have anticancer activity. Studies show that cyanidin 3-rutinoside and cyanidin 3-glucoside inhibit growth and spreading of highly metastatic A549 human lung carcinoma cells in absence of toxicity and may be of great value in developing a potential cancer therapy.

Cyanidin-3-O-beta-glucopyranoside (C3G) is an anthocyanin contained in oranges, blackberries, strawberries and cranberries. Hull Thornless blackberry cultivar has significantly higher anthocyanin, total phenolic content, antioxidant and antiproliferation activity than other cultivars. Cyanidin-3-glucoside inhibits cancerous transformation, metastasis, cell migration and invasion, and activation of tumor markers NF-[kappa]B, COX-2, TNF-[alpha], AP-I and MAPK, and induces death in cancer cells. Cyanidin-3-glucoside also possesses strong antioxidant activity and can inhibit generation of reactive oxygen species and induce an antioxidant protective response.

Cancers that can be treated using cyanidin-3-glucoside include skin cancer and lung cancer as it was discovered that cyanidin-3-glucoside not only treats or inhibits cancer, but also reduces or avoids metastasis of malignant cells. Because cyanidin-3-glucoside is known to be present in edible foodstuffs, this compound is expected to be a well-tolerated and safe therapy for treatment of neoplasia (such as skin or lung cancer) and metastasis. This benefit of cyanidin-3-glucoside is in stark contrast to traditional chemotherapy methods, many of which have toxic side effects. Skin cancer is the most common type of cancer in the United States and, in many cases, is associated with and promoted by exposure of the skin to ultraviolet radiation. Some traditional treatments for skin cancer involve topical chemotherapy with anticancer drugs in a lotion or cream applied to the skin. One such skin cancer treatment involves fluorouracil applied to the skin daily for several weeks. Intense inflammation is common as a result of fluorouracil treatment. Advantageously, cyanidin-3-glucoside occurs naturally in fruit and berries and is well tolerated when contacted to the skin (or other exposed body surface) of a patient.

Blackberry juice containing cyanidin-3-O-glucoside is a scavenger of peroxynitrite and that exert a protective effect against endothelial dysfunction and vascular failure induced by peroxynitrite. The peroxynitrite anion can react with DNA, proteins, and lipids at physiological conditions, leading to cellular damage.

Fruits and berries that contain cyanidin-3-glucoside include blueberries, strawberries, bilberries, cranberries, grapes, raspberries, elderberries, cherries, apples, purple corn, pomegranates, currants, gooseberries, chokeberries, rowanberries, blackberries, beans (such as black beans), grapefruit, eggplant, dogwood fruits (aka, Comellian cherries), oranges (for instance, Moro, Sanguinello or Tarocco oranges).

Western diets provide from several milligrams to a gram of flavonoids each day. Mixed diets contain flavonoids from all five subclasses. Most of the food flavonoids have glucose or some other sugar attached. These sugar-coated flavonoids are called falvonoid glycosides. Fruit and berry juices prepared using common commercial methods offer little anti-cancer and other health benefits from flavonoids.

Apples contain a variety of phytochemicals, including quercetin, catechin, phloridzin and chlorogenic acid, all of which are strong antioxidants. The phytochemical composition of apples varies greatly between different varieties of apples, and there are also small changes in phytochemicals during the maturation and ripening of the fruit. Storage has little to no effect on apple phytochemicals, but processing can greatly affect apple phytochemicals.

The apple peel powder has strong antioxidant activity and also greatly inhibits cancer cell proliferation. Another good news is that storage at 0°C for 9 months of apple peel has little effect on phenolic content. Processing of apples has been found to affect phytochemical content. Apple juice obtained from Jonagold apples by pulping and straight pressing had 10% of the antioxidant activity of fresh apples, while juice obtained after pulp enzyming had only 3% of antioxidant activity. Fourty-two percent of total phenolics were extracted in the juice, leaving over half the total phenolics in the apple pomace. Hydroxycinnamic acids acids and dihydrochalcones showed the greatest extraction yields in the juice, 65% and 80 % respectively. Procyanidins had the lowest yield in the juice (32%). Apple phenolics, especially procyanidins, have been found to bind with cell wall material, which could lead to the decreased levels of polyphenols found in apple juices. It has been proved that apple procyanidins suppress lipid accumulation in vascular wall, a process that plays multiple roles in the development of cardiovascular diseases.


  1. Pei-Ni Chena, Shu-Chen Chub, Hui-Ling Chiouc, Wu-Hsien Kuoa, Chui-Liang Chiangb and Yih-Shou Hsieha. Mulberry anthocyanins, cyanidin 3-rutinoside and cyanidin 3-glucoside, exhibited an inhibitory effect on the migration and invasion of a human lung cancer cell line.
  2. Ivana Serrainoa, Laura Dugoa, Paola Dugob, Luigi Mondelloc, Emanuela Mazzond, Giovanni Dugoc, Achille Patrizio Caputia and Salvatore Cuzzocreaa. Protective effects of cyanidin-3-O-glucoside from blackberry extract against peroxynitrite-induced endothelial dysfunction and vascular failure.
  3. Interaction of dietary compounds, especially polyphenols, with the intestinal microbiota: a review
  4. Apple phytochemicals and their health benefits. Jeanelle Boyer1 and Rui Hai Liucorresponding author1 Nutr J. 2004; 3: 5. doi: 10.1186/1475-2891-3-5
  5. Procyanidins are potent inhibitors of LOX-1: a new player in the French Paradox. Taichi NISHIZUKA, Yoshiko FUJITA, Yuko SATO1 Atushi NAKANO, Akemi KAKINO, Shunji OHSHIMA, Tomomasa KANDA, Ryo YOSHIMOTO, and Tatsuya SAWAMURA Proc Jpn Acad Ser B Phys Biol Sciv.87(3); 2011 Mar 11

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