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aa NUTR 420 > polyphenols > Flashcards

polyphenols Flashcards

1
Q

Polyphenols

A

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

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2
Q

Ellagic acid -

A

grapes, berries
antioxidant
- anticarcinogen

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3
Q

Tannins

A

fruits, teas

    - bind metals
    - precipitate proteins
    - antioxidants

condensed not as welly absorded

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4
Q

First observation on biological activities of flavonoids was made by

A

Szent-Györgyi and co-workers in 1936.

Mixture of citrus flavonoids (“citrin”) could exert a vitamin activity

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5
Q

Polyphenols - Structure

Common structural features of polyphenols:

A

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

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6
Q

Polyphenolic compounds can be divided into several different classes

2 major classes

A

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

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7
Q

flavanoid

A

3 rings- 2 benzenes and one center ring has an oxygen in the ring

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8
Q

phenolic acid

A

1 benzene ring and carbocylic acid- smaller, for examples caffeic acids

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9
Q

The antioxidant activity of polyphenols is influenced by:

A

the number and position of the hydroxyl groups

the extent of conjugated double bonds

lipid/aqueous solubility

ability to bind metals

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10
Q

Epidemiological studies:

A

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

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11
Q

Different factors influence the dietary intake of polyphenols such as:

A

Plant genetics and environmental conditions (amount of sunlight)
Ripeness (go from green to purple
Processing & storage

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12
Q

Polyphenols - Intake

Total Polyphenols
Phenolic Acids

Flavonoids

A

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

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13
Q

Polyphenol Absorption:

_influenced by degree of

A

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

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14
Q

Effects on Digestibility:

A

inhibit enzymes –> post-prandial glycemic response
( decrease glucose uptake too fast - good) some polyphenols & condensed tannins  hypocholesterolemic effects in rats

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15
Q

Metabolism – Intestine and Liver

A

polyphenols get metholated and can also get glucuronic acids attached to it

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16
Q

flavanol

A

onions, gingerm brocoli, asparagus , leafy greens

17
Q

Mechanisms of Flavonoid Health Effects

A

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)

18
Q

Health Effects of Flavonoids on cancer

mechanism

A 
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

19
Q

Phenolic acids

A

Salicylic acid – peppermint, licorice, peanut, wheat.
Vanillin – vanilla beans, cloves.
Gallic acid – tea, mango, strawberries, rhubarb, soy.
Tannic acid – nettles, tea, berries.

20
Q

Protocatechuic acid

A

A major metabolite of catechins and anthocyanins

Antioxidant and anti-inflammatory activities

21
Q

Effects of phenolic acids:

A

More water soluble than flavonoid aglycones
Most effects related to antioxidant activities
Action towards enzymes involved in metabolism of dopamine and catecholamines

22
Q

Teas

CVD:

Cancer prevention:

A 
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

23
Q

Wine

what

effects

A

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

24
Q

Beer

A 
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
25
Q

Cocoa & Chocolate

A

high amounts of catechin and epicatechin polymers (proanthocyanidins)

Dark, but not milk chocolate associated with increase in the total antioxidant capacity of plasma
Main cocoa flavonoids beneficial effects are related to cardiovascular health:
- antioxidant activities (decrease lipid oxidation)
- decrease platelet aggregation (increase prostacyclin levels & decrease leukotrienes)

26
Q

Olive Oil & Sesame Oil

A

Beneficial health effects on cardiovascular disease and cancer
Main polyphenols in olive and sesame oil:
tyrosol, Sesaminal

27
Q

Olive Oil effects

A

Hydroxytyrosol and oleuropein - ortho-diphenolic (2 adjacent hydroxyl groups) structure -> antioxidant activity

28
Q

Sesame Oil effects

A

lignans sesaminol and sesamolin  antioxidant effects

  • inhibition of lipid peroxidation of human LDL in vitro
  • in rats, lowered amounts of 8-OHdG, a marker of oxidative DNA damage
29
Q

Soy and Flaxseed

A

Plant isoflavones and lignans –> phytoestrogens

30
Q

Soybeans contain

A

high amounts of the glycosides of isoflavones: genistein & daidzein

Soy isoflavones may reduce breast cancer by altering endogenous sex-hormones and menstrual cycle
The mechanism proposed:
Isoflavones would stimulate sex-hormone binding proteins (SHBG) lowering free sex hormones concentration –> longer menstrual cycle –> protection against cancer development

31
Q

Soy

Genistein:

A

induces tumour-cell differentiation and inhibits angiogenesis
inhibition of platelet aggregation - may act as a Thromboxane A2 receptor antagonist
Previously held belief that decreases blood cholesterol levels not substantiated

32
Q

Flaxseed

A

Most abundant food source of lignans
- secoisolariciresinol and matairesinol

Lignans undergo metabolic transformation by the gut microflora, resulting in the formation of hormone-like compounds (enterolactone and equol)
Lignans in flaxseed, rye and bran protect against colon cancer not only through the formation of enterolactone, but also by fermentation and formation of butyrate
Possible hypocholesterolemic effects

33
Q

Mangosteen

A

Delicacy in tropical Asia
Not commonly imported due to fear of Asian fruit fly infestation (but some irrad imports and cultivated in Hawaii)
Pericarp has red-purple juice containing xanthones
-eg. α-mangostin
Normally eat white fleshy centre but juice made from whole fruit (eg. Xango)

Several biological effects reported
Anticancer – induces apoptosis
-mitochondrial swelling
Anti-inflammatory - decrease histamine and prostaglandin E release
Anti-bacterial
Antioxidant
34
Q

Conclusions

A

Polyphenols - wide range of compounds that influence human health
Potential to be applied in the prevention and treatment of human chronic diseases such as inflammation, metabolic syndrome, CVD and cancer
Trends for future investigations:
Bioavailability, metabolism, distribution,
Differences in effects and potencies
Long-term effects of chronic exposure

35
Q

Apple browning: enzymatic browning- oxidation of polyphenols makes it brown.- lemons denature the enzymes responsible for the browning, vitamin c can reduce the oxidized form to the reduced form
Blanching: would also denature the enzyme, coat with sugar- prevents oxygen from getting to it, dip in sulfites- reduces everythi
Enzymatic browning:
Catalysed by polyphenol

A

s

36
Q

Antioxidant Phytochemicals Block NFB Activation

A

If NFkB goes to nucleus- inflammation

Antioxydants scavenge the ROS , they protect phosphatases, so they can limit the
Antioxydants prevent NFKB from forming inflammation

37
Q

Health Effects of Flavonoids

Effects on cardiovascular disease:

A

Diminished susceptibility of LDL to lipid peroxidation  anti-atherogenic effect
Inhibition of platelet aggregation, nitric oxide production and TNF- production  anti-thrombogenic effect
Vasodilatory effects (some flavonoids)

38
Q

Resveratrol

A

Resveratrol – weak antioxidant  possible protection of LDL oxidation
Resveratrol - most potent polyphenol activator of sirtuin deacetylases (promote cell survival and extend lifespan)
Resveratrol - chemopreventive activity by inhibiting COX1 and COX2 involved in the production of prostaglandins (same inhibition of aspirin and ibuprofen)

aa NUTR 420 (10 decks)

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