Anthocyanins, synthesized via the flavonoid pathway, are a class of crucial phenolic compounds which are fundamentally responsible for the red color of grapes and wines. As the most important natural colorants in grapes and their products, anthocyanins are also widely studied for their numerous beneficial effects on human health. In recent years, the biosynthetic pathway of anthocyanins in grapes has been thoroughly investigated. Their intracellular transportation and accumulation have also been further clarified. Additionally, the genetic mechanism regulating their biosynthesis and the phytohormone influences on them are better understood. Furthermore, due to their importance in the quality of wine grapes, the effects of the environmental factors and viticulture practices on anthocyanin accumulation are being investigated increasingly. The present paper summarizes both the basic information and the most recent advances in the study of the anthocyanin biosynthesis in red grapes, emphasizing their gene structure, the transcriptional factors and the diverse exterior regulation factors.

Originating in the grapes, monomeric anthocyanins in young red wines contribute the majority of color and the supposed beneficial health effects related to their consumption, and as such they are recognized as one of the most important groups of phenolic metabolites in red wines. In recent years, our increasing knowledge of the chemical complexity of the monomeric anthocyanins, their stability, together with the phenomena such as self-association and copigmentation that can stabilize and enhance their color has helped to explain their color representation in red wine making and aging. A series of new enological practices were developed to improve the anthocyanin extraction, as well as their color expression and maintenance. This paper summarizes the most recent advances in the studies of the monomeric anthocyanins in red wines, emphasizing their origin, occurrence, color enhancing effects, their degradation and the effect of various enological practices on them.

Originating in the grapes, anthocyanins and their derivatives are the crucial pigments responsible for the red wine color. During wine maturation and aging, the concentration of monomeric anthocyanins declines constantly, while numerous more complex and stable anthocyanin derived pigments are formed, mainly including pyranoanthocyanins, polymeric anthocyanins produced from condensation between anthocyanin and/or flavan-3-ols directly or mediated by aldehydes. Correspondingly, their structural modifications result in a characteristic variation of color, from purple-red color in young red wines to brick-red hue of the aged. Because of the extreme complexity of chemical compounds involved, many investigations have been made using model solutions of know composition rather than wine. Thus, there is a large amount of research still required to obtain an overall perspective of the anthocyanin composition and its change with time in red wines. Future findings may well greatly revise our current interpretation of the color in red wines. This paper summarizes the most recent advances in the studies of the anthocyanins derived pigments in red wines, as well as their color evolution.

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The accumulation of phenolics in the skins of two Vitis davidii cultivars ('Ziqiu' and 'Xiangzhenzhu') and one Vitis quinquangularis cultivar ('Xiangshan No. 4') native to China was followed during ripening. It was found that the anthocyanin composition of all three grapes was dominated by anthocyanidin 3,5-O-diglucosides. The cultivar 'Xiangshan No. 4' (V. quinquangularis) contained a high level of 3',4'-substituted anthocyanins and low levels of flavonols and 3',4'-substituted flavan-3-ols, indicating that the F3'H branch pathway was the principal carbon pathway synthesizing mainly 3',4'-substituted anthocyanins. No myricetin-type flavonols were found in this cultivar, but in both 'Ziqiu' and 'Xiangzhenzhu' (V. davidii) cultivars the F3'5'H branch pathway was dominant, resulting in malvidin-based diglucoside anthocyanins. Cyanidin-based and petunidin-based anthocyanins were not detected in the 'Ziqiu' cultivar. Principal component analysis revealed that V. davidii grapes had abundant flavonols by the early middle developmental stages and a high level of malvidin-type anthocyanins by the late developmental stage. In contrast, the V. quinquangularis cultivar contained other anthocyanins instead of malvidin-type anthocyanins.

Proanthocyanidins are a group of oligomeric or polymeric flavan-3-ols that are highly significant contributors to astringency in grapes and wines. An orthogonal L9(3) 4 test was adopted to determine the optimal extraction conditions and acid-catalysis cleavage of proanthocyanidins in the presence of excess phloroglucinol. The qualitative and quantitative analyses were done using HPLC-DAD-ESI-MS/MS. The results showed that the maximum extraction was obtained using 0.3 mol/L of HCl and 0.005 g of ascorbic acid with incubation at 70°C for 20 min. The precision and accuracy of this method were acceptable. The composition of free flavan-3-ols and proanthocyanidins in the skins of 'Marselan' grapes (Vitis vinifera L. cv.) was investigated. (-)-Epigallocatechin was found to be the most abundant free flavan-3-ol monomer and terminal subunits, whereas the extension subunits were mainly (-)-epicatechin-3-O-gallate in the early developmental stages, and primarily (-)-epigallocatechin and (-)-epicatechin in the middle and late stages.

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