Wednesday, January 1, 2014


Many of the most common plant pigments are known as FLAVONOID. These flavonoids are consumed as part of the human diet and responsible for much of the flavor and color of fruits and vegetables. In addition the flavonoids are just one of the many classes of nutraceuticles present in our diet. They can be divided into several groups based on their structure.
  • The flavones and flavonols give yellow or orange colors
  • The anthocyanins give red, violet or blue colors.
  • The aurones are golden yellow pigments.
  • The flavanones and flavanonols are either colorless or only slightly yellow.


Dietary flavonoids are preventives or prophylactics rather than therapeutics. Dietary flavonoids give both nutrition as well as medicinal benefits. Natural food-derived flavonoids may help reduce the incidence of non-communicable diseases mainly atherosclerosis, cancer, cardiovascular diseases, diabetes, thrombosis, inflammation in arthritis, asthma, encephalomyelitis, and neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases, obesity, hyperlipidemia, nerve injury, and hypertension.

Flavonoids are rich in fresh fruits, vegetables and nuts. Differences in cultivars and growing conditions may lead to differences in the relative amounts of dietary flavonoids. Common flavan-3-ols present in these sources are catechin, catechin gallate, epicatechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate, gallocatechin, and gallocatechin gallate.

Dietary flavonoids also include the anthocyanins cyanidin, delphinidin, malvidin, pelargonidin, peonidin and petunidin together with the flavanones hesperetin and naringenin, the flavones apigenin and luteolin, and the flavonols myricetin, kaempferol, and quercetin.

The most abundant dietary flavonol is Quercetin. It is present in black and green teas, onions, apples, grapes, beans, broccoli, lettuce, berries, oregano, mangoes, and tomatoes, among others. Coffee contains myricetin. Flavored black teas, with higher levels of catechins, quercetin, and rutin, showed stronger anti-oxidant activity than fruit teas, which contained higher levels of naringin and hesperidin.

Quercetin inhibited the growth of several human cancer cell lines at different phases of the cell cycle by direct pro-apoptosis with almost total absence of damage for normal, non-transformed cells. Quercetin also inhibited the activation of peroxisome proliferator-activated receptor isoforms (PPARs) alpha, beta and gamma. PPARs are drug targets in metabolic syndrome, wherein obesity, hyperglycemia, hypertension, and hyper/dyslipidemia are all present. Quercetin and myricetin blocked the genotoxic effects of some cooked-food mutagens.

Berries are also rich in anthocyanins while black and green teas are also sources of flavan-3-ols. Red wine, which is rich in anthocyanins and flavonoids, inhibited the growth of human breast cancer cells (MCF-7) with relatively low cytotoxicity towards normal human mammary epithelial cells and a non-tumorigenic MCF- 10A cell line. Apples contain high levels of flavonols, catechins, and oligomeric procyanidins. Red apples are rich in anthocyanidins. Apple extracts prevented skin, mammary and colon cancers in animal models. Apple extracts also exhibited anti- inflammatory activity.

Fruits and vegetables rich in anthocyanins, such as strawberry, raspberry and red plum, were potent antioxidants, followed by those rich in flavanones, such as orange and grapefruit, and flavonols, present in onion, leek, spinach and green cabbage, while the hydroxycinnamate-rich apple, tomato, pear and peach consistently elicited lower antioxidant activities. Bananas also showed antioxidant activity against rats fed normal as well as high fat diets. The antioxidant activity of strawberry against PC12 cells, a model system for neuronal differentiation, treated with hydrogen peroxide was higher than banana and orange. The reduction of oxidative stress-induced neurotoxicity and the higher neuroprotective activity of strawberry may be due to its higher anthocyanins content compared to banana and orange. Broccoli provided anti-oxidants, regulated enzymes and controlled apoptosis and cell cycle. Yellow and red onion bulbs contain flavonols  as well as anthocyanins and dihydroflavonols. Citrus fruits contain flavanones. The major flavone sources are parley, celery, and English spinach while the major anthocyanidin source is wine. Tea, legumes, and wines contributed to 48% of daily intake of proanthocyanidins. Durian, pomelo, guava, and ripe banana are good sources of flavonoids.

Reference

  • Irene M. Villasenor , Nutraceuticals: Dietary Flavonoids, Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101, irene.villasenor@up.edu.ph
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