polyphenols Flashcards
(38 cards)
Polyphenols
Polyphenols widespread compounds found in plants (fruits, vegetables, cereals, grains)
In the past:
- attention drawn to the antinutritional effects (ability to bind and precipitate nutrients and digestive enzymes)
Now:
- focus on beneficial health effects based mainly on their antioxidant activities
Ellagic acid -
grapes, berries
antioxidant
- anticarcinogen
Tannins
fruits, teas
- bind metals
- precipitate proteins
- antioxidants
condensed not as welly absorded
First observation on biological activities of flavonoids was made by
Szent-Györgyi and co-workers in 1936.
Mixture of citrus flavonoids (“citrin”) could exert a vitamin activity
Polyphenols - Structure
Common structural features of polyphenols:
About 8000 different plant polyphenols have been identified (from simple compounds to highly polimerized structures)
Common structural features of polyphenols:
conjugated aromatic ring
with at least two hydroxy (OH) substituents
Polyphenolic compounds can be divided into several different classes
2 major classes
Flavonoids: major polyphenols in the human diet (~1/2 of the total phenols)
Phenolic acids: account for ~1/3 of the total phenols from the diet
Lignans
Others
flavanoid
3 rings- 2 benzenes and one center ring has an oxygen in the ring
phenolic acid
1 benzene ring and carbocylic acid- smaller, for examples caffeic acids
The antioxidant activity of polyphenols is influenced by:
the number and position of the hydroxyl groups
the extent of conjugated double bonds
lipid/aqueous solubility
ability to bind metals
Epidemiological studies:
diets rich in fruits and vegetables associated with reduced risk of chronic disease
Protective effects due to synergistic effects of the mixture of polyphenols
Examples:
Mediterranean diet
French paradox (LOTS OF FAT IN DIET, but incident of heart disease was very low- determined that red wine contributed to this)
- both associated with protection from CVD
Different factors influence the dietary intake of polyphenols such as:
Plant genetics and environmental conditions (amount of sunlight)
Ripeness (go from green to purple
Processing & storage
Polyphenols - Intake
Total Polyphenols
Phenolic Acids
Flavonoids
Total Polyphenols
863 mg/day in Finland (Ovaskainen et al. 2008)
75% phenolic acids, 14% proanthocyanidins, 10% other flavonoids
Phenolic Acids
222 mg/d in Germany (Radtke et al 1998)
500-800 mg/d in UK for moderate coffee drinkers who also eat citrus fruits and bran (Clifford 1999)
190 mg/day in US (Chun et al 2007)
83.5% flavan-3-ols (catechins), 7.6% flavanones, 6.8% flavonols, 1.6% anthocyanidins, 0.8% flavones, and 0.6% isoflavones
454 mg/day in Australia (Johannot & Sommerset 2006)
93% flavan-3-ols from black tea
Polyphenol Absorption:
_influenced by degree of
glycosylation
In general aglycone more readily absorbed
-small intestine glycosidase activity
-intestinal bacteria some glycosidase act.
glucose moiety enhances quercetin absorption, other sugars (eg. rutinose, rhamnose, galactose) inhibit
Highly polymerized polyphenols not well absorbed
Effects on Digestibility:
inhibit enzymes –> post-prandial glycemic response
( decrease glucose uptake too fast - good) some polyphenols & condensed tannins hypocholesterolemic effects in rats
Metabolism – Intestine and Liver
polyphenols get metholated and can also get glucuronic acids attached to it
flavanol
onions, gingerm brocoli, asparagus , leafy greens
Mechanisms of Flavonoid Health Effects
Antioxidant activity: ability to donate a hydrogen atom from an aromatic hydroxyl group to a free radical
May work at interface of membranes
Anti-inflammatory activity: inhibition of NfkB activation, inhibition of enzymes (cyclooxygenase, NADPH oxidase)
Health Effects of Flavonoids on cancer
mechanism
Effects on cancer: Antiproliferative Pro-apoptotic Anti-inflammatory Anti-angiogenic
Mechanisms involved:
- antioxidant/pro-oxidant activities
- modulation of cytochrome P450 enzymes involved in activating carcinogens
- inhibition of COX2 and iNOS involved with inflammation
- anti-estrogenic activity (isoflavones)
Anti-estrogen: isoflavones are weak estrogens so binbd to receptors, so in premenopause they compete and are weak. Post menopause- thought that the weak estrogenic effect can help things such as bone so high soy might help. In cancers- it might makes things worse but no research to support. So huge protection seen
Phenolic acids
Salicylic acid – peppermint, licorice, peanut, wheat.
Vanillin – vanilla beans, cloves.
Gallic acid – tea, mango, strawberries, rhubarb, soy.
Tannic acid – nettles, tea, berries.
Protocatechuic acid
A major metabolite of catechins and anthocyanins
Antioxidant and anti-inflammatory activities
Effects of phenolic acids:
More water soluble than flavonoid aglycones
Most effects related to antioxidant activities
Action towards enzymes involved in metabolism of dopamine and catecholamines
Teas
CVD:
Cancer prevention:
Main flavonoids in green and black tea - catechins, theaflavins and thearubigens CVD: d LDL oxidation, d cholesterol levels d blood pressure
Cancer prevention:
Free radical scavenging
Anti-inflammatory
increase carcinogen detoxification
Wine
what
effects
Polyphenols
Moderate alcohol consumption: protective against CVD by increase HDL levels and inhibiting platelet aggregation
proanthocyanin, resveratrol, anthocyanin
d lipid peroxidation
increase plasma antioxidant capacity in humans
Vasodilation - promotion of NO synthesis by the vascular endothelium
Anti-thrombotic - inhibition of platelet thomboxane A2 synthesis (COX1) -> decrease platelet aggregation
Beer
Contains soluble fibre (ß-glucans)! - 12 oz lager 1-2 g, stout 2-3.5 g Hops (Humulus lupulus) Humulone & Lupulone Bitter principles Antibacterial Stimulate appetite Sedative and soporific effects Anti-inflammatory – inhibit COX2 Anti-angiogenic activity - suppress proliferation of endothelial cells
