- 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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