Flavinoids are a large group of plant polyphenols. These compounds usually occur bound to sugar molecules. Phytochemicals are naturally occurring plant compounds such as cocoa, so flavinoids are also classed as phytochemicals. Some phytochemicals are thought to play a role in maintaining health, others may be toxic. Polyphenols are a broad class of antioxidant phytochemicals that are found throughout the plant kingdom. An example are procyanidins, a class of polyphenolic compounds found in several foods such as apples, almonds, barley, grapes, tea, maize, cinnamon, cocoa, peanuts, wine and strawberries. Procyanidins may act as antioxidants and modulate key biological pathways in mammals. A phytoestrogen found in red grape skin called Resveratrol is an antioxidant. It is also found in mulberries, peanuts, knotweed (polygonum cuspidatum) and red wine.
Resveratrol helps lower cholesterol, and is as much as 10 to 20 times more potent than vitamin E in protecting against LDL oxidation, a process that has been linked to the development of cardiovascular disease. It is also thought to discourage tumor growth by blocking the action of Cox-2, an enzyme that researchers believe contributes to the development of colon cancer. Additional studies suggest that resveratrol may be useful in both preventing and treating cancer.
Resveratrol is found in the stems, leaves, and skins of grapes. Although a glass or two of red wine each day may lower the risk of heart disease, one recent study shows that alcohol-free red wine works just as well. Resveratrol is also present in purple grape juice, red or purple grapes, and peanuts. However, because of the fermenting process, resveratrol levels are higher in red wine than other natural sources; red wine has about three times as much resveratrol as grape juice.
Epidemiological studies show that a high polyphenol diet can reduce the risk of coronary heart disease and stroke. Polyphenols inhibit the oxidation of low-density lipoproteins (LDLs). They reduce the risk of atherosclerosis developing by preventing LDL (bad cholesterol), from building plaque in the arteries, while raising the levels of HDL, the good cholesterol. Atherosclerosis may be initiated by oxidised LDL.
Flavonoids are a specific sub-class of compounds within the general flavonoid classification found in cocoa, chocolate, green tea, grapes, apples and red wine (Chocolate Information Centre).
Flavonoids are subdivided into 13 classes, based on the degree of hydroxylation and oxidation of the rings. Flavonoid types include anthocyanins (pigmented compounds), flavonols (such as quercetin), isoflavones (genistein and diadzein), flavanols (such as catechin), and proanthocyanidins or condensed tannins (Steinberg et al, 2003).
Phenolics, especially flavonoids, are suggested as being essential bioactive compounds providing health benefits. Fruits and vegetables contain antioxidant compounds broadly called polyphenols that are known to reduce oxidative stress and prevent chronic diseases (Ninfali et al, 2005). The antioxidant properties of these compounds are responsible for their anticancer, antiviral and anti-inflammatory properties (Cao et al. 1997). They can also prevent capillary fragility and platelet aggregation (Benavente- Garcia et al. 1997; Aviram, 1999). Each different vegetable or fruit cultivar ( i.e. of the same family) possesses significantly different phenolic, flavanol and ORAC values. This is clearly evident, for example, in lettuce, onion and pepper cultivars. Generally the red varieties like the lettuce Rossa di Trento have a higher phenolic content and antioxidant activity. Green cabbage shows one half of the phenolics, flavonoids and ORAC values of savory or black cabbage; moreover, savoy cabbage has a higher flavonoid content and higher ORAC values than black cabbage. A similar discrepancy between the cultivars is observed for the radish.
Ninfali et al., 2005
Only the raw and seasonally harvested (fresh) vegetables are able to exhibit in vitro their maximal antioxidant capacity owing to their intact phenolic and flavanol contents. The type of cooking also affects total phenolics.
Aviram M (1999) Antiatherogenicity of antioxidants against LDL oxidation. In Natural Antioxidants and Anticarcinogens in Nutrition, Health and Disease, pp. 9–19 [JT Kumpulainen and
JT Solonen, editors]. Cambridge: Royal Society of Chemistry.Benavente-Garcia O, Castillo J, Marin FR, Ortuno A & del RiovJA (1997) Use and properties of citrus flavonoids. J AgricvFood Chem 45, 4505–4515.
Cao G, Sofic E & Prior RL (1997) Antioxidant and prooxidant behavior of flavonoids: structure–activity relationship. Free Rad Biol Med 22, 749–760.
Ninfali P, Mea G, Giorgini S, Rocchi M, & Bacchiocca M. (2005). Antioxidant capacity of vegetables, spices and dressings relevant to nutrition. The British Journal of Nutrition. 93 (2), 257-66.
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