A grape is a non-climacteric fruit, specifically a berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or they can be used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, molasses and grape seed oil. Grapes are also used in some kinds of confectionery. Grapes are typically an ellipsoid shape resembling a prolate spheroid.
Grapes are a type of berry that grow in clusters of 15 to 300, and can be crimson, black, dark blue, yellow, green, orange, and pink. “White” grapes are actually green in color, and are evolutionarily derived from the purple grape. Mutations in two regulatory genes of white grapes turn off production of anthocyanins which are responsible for the color of purple grapes.Anthocyanins and other pigment chemicals of the larger family of polyphenols in purple grapes are responsible for the varying shades of purple in red wines.
Most grapes come from cultivars of Vitis vinifera, the European grapevine native to the Mediterranean and Central Asia. Minor amounts of fruit and wine come from American and Asian species such as:
- Vitis labrusca, the North American table and grape juice grapevines (including the concord cultivar), sometimes used for wine, are native to the Eastern United States and Canada.
- Vitis riparia, a wild vine of North America, is sometimes used for winemaking and for jam. It is native to the entire Eastern U.S. and north to Quebec.
- Vitis rotundifolia, the muscadines, used for jams and wine, are native to the Southeastern United States from Delaware to the Gulf of Mexico.
- Vitis amurensis is the most important Asian species.
Health claims
Comparing diets among Western countries, researchers have discovered that although the French tend to eat higher levels of animal fat, surprisingly the incidence of heart disease remains low in France. This phenomenon has been termed the French Paradox, and is thought to occur from protective benefits of regularly consuming red wine. Apart from potential benefits of alcohol itself, including reduced platelet aggregation and vasodilation,polyphenols (e.g., resveratrol) mainly in the grape skin provide other suspected health benefits, such as:
- Alteration of molecular mechanisms in blood vessels, reducing susceptibility to vascular damage
- Decreased activity of angiotensin, a systemic hormone causing blood vessel constriction that would elevate blood pressure
- Increased production of the vasodilator hormone, nitric oxide (endothelium-derived relaxing factor)
Although adoption of wine consumption is not recommended by some health authorities,a significant volume of research indicates moderate consumption, such as one glass of red wine a day for women and two for men, may confer health benefits. Emerging evidence is that wine polyphenols like resveratrolprovide physiological benefit whereas alcohol itself may have protective effects on the cardiovascular system.
Anthocyanins and other phenolics
Anthocyanins tend to be the main polyphenolics in purple grapes whereas flavan-3-ols (i.e. catechins) are the more abundant phenolic in white varieties. Total phenolic content, a laboratory index of antioxidant strength, is higher in purple varieties due almost entirely to anthocyanin density in purple grape skin compared to absence of anthocyanins in white grape skin. It is these anthocyanins that are attracting the efforts of scientists to define their properties for human health. Phenolic content of grape skin varies with cultivar, soil composition, climate, geographic origin, and cultivation practices or exposure to diseases, such as fungal infections.
Red wine may offer health benefits more so than white because potentially beneficial compounds are present in grape skin, and only red wine is fermented with skins. The amount of fermentation time a wine spends in contact with grape skins is an important determinant of its resveratrol content. Ordinary non-muscadine red wine contains between 0.2 and 5.8 mg/L, depending on the grape variety, because it is fermented with the skins, allowing the wine to absorb the resveratrol. By contrast, a white wine contains lower phenolic contents because it is fermented after removal of skins.
Wines produced from muscadine grapes may contain more than 40 mg/L, an exceptional phenolic content. In muscadine skins, ellagic acid, myricetin, quercetin, kaempferol, and trans-resveratrol are major phenolics. Contrary to previous results, ellagic acid and not resveratrol is the major phenolic in muscadine grapes. The flavonols syringetin, syringetin 3-O-galactoside, laricitrin and laricitrin 3-O -galactoside are also found in purple grape but absent in white grape.