Polyphenols are a large family of naturally occurring phenols.
Polyphenols are a large and diverse class of naturally occurring organic compounds characterized by the presence of multiple phenolic structural units (aromatic rings with hydroxyl groups).
They are abundant in plants and structurally diverse.
Polyphenols include phenolic acids, flavonoids, tannic acid, and ellagitannin, some of which have been used historically as dyes and for tanning garments.
Curcumin, a bright yellow component of turmeric is a polyphenol.
Polyphenols are natural products with hydroxyl groups on aromatic rings, including four principal classes: phenolic acids, flavonoids, stilbenes, and lignans.
Flavonoids can be grouped as flavones, flavonols, flavanols, flavanones, isoflavones, proanthocyanidins, and anthocyanins, phenolic acids, stilbenes, lignans, tannins, and anthocyanidins.
Particularly abundant flavanoids in foods are catechin (tea, fruits), hesperetin (citrus fruits), cyanidin (red fruits and berries), daidzein (soybean), proanthocyanidins (apple, grape, cocoa), quercetin (onion, tea, apples), wine, vegetables, cereals, tea, coffee, wine, and chocolate.
They are secondary metabolites produced by plants, serving protective roles against environmental stressors such as ultraviolet radiation, pathogens, and herbivores.
Their biological activities are primarily attributed to their antioxidant properties, that involve scavenging reactive oxygen species (ROS), modulating cellular signaling pathways, and influencing gene expression.
In addition to antioxidative effects, polyphenols exhibit anti-inflammatory, cardioprotective, anticancer, and metabolic regulatory activities, with evidence supporting their role in the prevention and management of chronic diseases including cardiovascular disease, diabetes, obesity, neurodegenerative disorders, and cancer.
Polyphenols undergo extensive metabolism, resulting in a variety of bioactive metabolites that contribute to their health effects.
Polyphenols also include phenolic acids, such as caffeic acid, and lignans, which are derived from phenylalanine present in flax seed and other cereals.
Polyphenols: generally are moderately water-soluble compounds with molecular weight of 500–4000 Da.
Mainly found in the fruit skins and seeds.
Black tea contains high amounts of polyphenol and makes up for 20% of its weight.
Some polyphenols are traditionally used as dyes in leather tanning, silver-based photography, green chemicals, plastics or resins by polymerization with formaldehyde, as well as adhesives for particleboards.
The most abundant polyphenols are the condensed tannins, found in virtually all families of plants.
Larger polyphenols are often concentrated in leaf tissue, the epidermis, bark layers, flowers and fruits.
Larger polyphenols play important roles in the decomposition of forest litter, and nutrient cycles in forest ecology.
Polyphenols are thought to play diverse roles in the ecology of plants: Release and suppression of growth hormones such as auxin. UV screens to protect against ionizing radiation and to provide coloration Deterrence of herbivores Prevention of microbial infections Signaling molecules in ripening and other growth processes. In some woods natural preservation against rot.
Polyphenols comprise up to 0.2–0.3% fresh weight for many fruits.
Consuming common servings of wine, chocolate, legumes or tea may also contribute to about one gram of intake per day.
The most important food sources are widely consumed in large quantities such as fruit and vegetables, green tea, black tea, red wine, coffee, chocolate, olives, and extra virgin olive oil.
Herbs and spices, nuts and algae are also potentially significant for supplying certain polyphenols.
Some polyphenols are specific to particular food (flavanones in citrus fruit, isoflavones in soya, phloridzin in apples); whereas others, such as quercetin, are found in all plant products such as fruit, vegetables, cereals, leguminous plants, tea, and wine.
Some polyphenols are compounds that interfere with the absorption of essential nutrients – especially iron and other metal ions, which may bind to digestive enzymes and other proteins, particularly in ruminants.
Phenolic and carotenoid levels in vegetables are retained better by steaming compared to frying.
Astringency increases and bitterness decrease with the mean degree of polymerization.
Polyphenols are not considered nutrients, as they do not contribute to growth, survival, or reproduction, nor do they provide dietary energy.
Therefore, they do not have recommended daily intake levels, such as those for vitamins, minerals, and fiber.
Polyphenols cannot be mentioned on food labels as antioxidant nutrients unless physiological evidence exists to verify such a qualification and a Dietary Reference Intake value has been established – characteristics which have not been determined for polyphenols.
Flavanols in cocoa solids at doses exceeding 200 mg per day may contribute to maintenance of vascular elasticity and normal blood flow; olive oil polyphenols may contribute to the protection of blood lipids from oxidative damage, if consumed daily.
Most polyphenols are metabolized by catechol-O-methyltransferase, and therefore do not have the chemical structure allowing antioxidant activity in vivo; they may exert biological activity as signaling molecules.
Some polyphenols are considered to be bioactive compounds.
For most polyphenols, there is no evidence for an effect on cardiovascular regulation.
Higher intakes of soy isoflavones may be associated with reduced risks of breast cancer in postmenopausal women and prostate cancer in men.
Intake of soy and soy isoflavones is associated with a lower risk of mortality from gastric, colorectal, breast and lung cancers.
Isoflavones, which are structurally related to 17β-estradiol, are classified as phytoestrogens.
Polyphenols are extensively metabolized by the gut microbiota and are investigated as a potential metabolic factor in function of the gut microbiota.
Adverse effects of polyphenol intake range from mild gastrointestinal tract symptoms to severe hemolytic anemia or hepatotoxicity).
Polyphenols, particularly in beverages that contain them in high concentrations (tea, coffee, etc), inhibit the absorption of non-haem iron when consumed together in a single meal.
Metabolism of polyphenols can result in flavonoid-drug interactions, such as in grapefruit–drug interactions, which involves inhibition of the liver enzyme, CYP3A4, likely by grapefruit furanocoumarins, a class of polyphenol.
For most polyphenols found in the diet, an adverse effect beyond nutrient-drug interactions is unlikely.