# Polypphenols: Natural Antioxidants to Be Used as a Quality Tool in Wine Authenticity
## 2 Structural Information
### Flavonoid Compounds
#### Anthocyanins  
Anthocyanins present an essential role in red wines as they impact on wine color as well as on reactions affecting the stability and longevity of red wines [70]. More than 540 anthocyanin pigments have been found in nature [70]. They exhibit a wide range of biological activities including antioxidant, anti-inflammatory, antimicrobial, antimutagenic, and anticarcinogenic properties [71]. In _V. vinifera_ grape varieties, they are mainly localized on red berry skins where they are synthesized from veraison until full ripening. Their content is significantly affected by vintage and overall vineyard management practices [9]. They have been also found present on the skins of some pink-skinned varieties such as Gewurtztraminer and Muscat Rouge de Madere [59] and in the pulp of the so called \"teinturer\" _V. vinifera_ (i.e., Alicante Bouchet) and non _V. vinifera_ grape varieties [72; 73; 74]. Malvidin, delphinidin, peonidin, cyanidin, petunidin, and lately pelargonidin [75; 76] are regarded as the most important anthocyanidins in wine (Figure 7). Their differentiation lies in the substituent groups present in the B-ring. In _Vitis vinifera_ grape varieties, the aglycon (anthocyanidin) is bonded through a glycosidic bond in position 3 of the ring C to a sugar moiety, commonly glucose. Malvidin-3-O-glucose has been proposed as the dominant anthocyanin in red grape varieties [17; 44; 59; 62]. Moreover, acylation can occur on the glucose moiety with aromatic (such as caffe, ferulic, sinapic, and \(p\)-coumaric acids) or aliphatic acids (such as acetic, malic, malonic, oxalic, and succinic acids) probably due to the presence of the enzyme anthocyanin acyl-transferase [9]. In winemaking, their extraction during maceration reaches a plateau before the end of the fermentation [49] with their concentration in young red wines typically ranging from 200 to 400 mg/L [49]. During wine maturation and aging, free form anthocyanin concentration declines constantly as they are involved in reactions between them and/or components such as proanthocyanidins and simple  
Figure 7: Main anthocyanin chemical structures. flavan-3-ols, forming more complex and stable products while affecting wine color and organoleptic characteristics [75]. These reactions mainly include:  
* Self-association and co-pigmentation (short-term mechanisms),
* Polymeric anthocyanins with proanthocyanidins and 3-flavanols (long-term mechanisms) and
* New formed compounds, such as pyranoanthocyanins and their polymerized compounds. Anthocyanins comparing to other flavonoid compounds do not intrinsically affect bitterness or astringency [77]. Although they have no odor or flavor, they can act in synergy with some aroma substances and influence wine flavor [78]. Regarding red vinication practices, it has been recently proposed that oxygen improves cycloaddition and enhances the formation of pyranoanthocyanins, while high microoxygenation rates and lower pH values enhance flavanol-pyranoanthocyanin contents. Moreover, micro-oxygenated red wines have been found richer in Vitisin A in comparison to the control [79]. In recent studies on non-Saccharomyces strains such as _Lachancea thermotolerans_, an intense effect of some strains was observed on anthocyanin color and stability by strongly reducing wine pH during the alcoholic fermentation [80]. In addition, selected Saccharomyces yeast strains have been shown to release metabolites such as acetaldehyde or pyruvate acid that promote the formation of Vitisin A and B pyranoanthocyanins during must fermentation [81]. Among phenolics, anthocyanins are regarded as the most successful compounds for red wine varietal authentication [82]. For instance, diglucoside anthocyanins displaying a second glycosidic bond at position 5\({}^{\prime}\) with glucose characterize non-_V. vinifera_ grapes and this has been successfully employed in chemotaxonomical studies [9].