Pyranoanthocyanins resulting from the addition of pyruvic acid or acetaldehyde to anthocyanins, contributing to wine color and color stability. Thi Nguyen, 2016
Among the pigments formed by reactions between anthocyanins and other wine constituents during aging is a class of compounds called pyranoanthocyanins, characterized by an added pyran ring between the C4 and the hydroxyl attached to the C5 of the original anthocyanin (Fulcrand et al. 1998, Alcade-Eon et al. 2006). While the cycloaddition required for the formation of pyranoanthocyanins may occur with a number of wine components, the addition of either pyruvic acid or acetaldehyde specifically to anthocyanins yields vitisins of types A and B respectively (Rentzsch et al. 2007a). First observed to augment wine color in 1976 by Timberlake and Bridle, vitisins have gained attention due to their contributions to wine color and color stability. Vitisins contribute 11-14 times more color than unmodified anthocyanins and exhibit a hypsochromic shift towards an orange-red hue, possibly due to the extended conjugation afforded by pyran ring (Bakker et al. 1997, Romero and Bakker 1999, Schwarz et al. 2003). Furthermore, in contrast to that of anthocyanins, the color expression of vitisins remains stable against discolouration by changes in pH or bleaching by sulfur dioxide. The pyran ring is thought to prevent hydration to form the carbinol form at high pH, as well as inhibit addition of bisulfite to form the flavene sulfonate, both of which are colorless due to loss of conjugation (Bakker and Timberlake, Schwarz et al. 2003).
Vitisin formation depends on the presence of anthocyanins and either pyruvic acid or acetaldehyde, therefore control of vitisin concentrations in wine begins with the management of these precursors throughout the winemaking process. Practices that increase extraction of anthocyanins from the skins of grape berries likely promote the formation of vitisins (Rentzsch et al. 2007b). Given that pyruvic acid and acetaldehyde are key intermediates in microbial metabolism, wine microbes may also influence vitisin formation. The selection of yeast strains that enhance anthocyanin extraction or excrete more pyruvic acid and acetaldehyde excretion may improve vitisin formation (Sacchi et al. 2005, Monagas et al. 2007). Delaying or forgoing malolactic fermentation can preclude consumption of pyruvic acid and acetaldehyde by lactic acid bacteria and subsequently increase the potential for vitisin synthesis (Asenstorfer et al. 2003, Burns and Osborne 2015). Oxidative processes that give rise to pyruvic acid and acetaldehyde, such as barrel aging and micro-oxygenation, have also been shown to increase vitisin levels, color intensity, and color stability (Alcade-Eon et al. 2006, Cano-Lopez et al. 2010, Anli and Cavuldak 2013).
References
- Alcade-Eon, C., M.T. Escribano-Bailon, C. Santos-Buelga, and J.C. Rivas-Gonzalo. 2006. Changes in the detailed pigment composition of red wine during maturity and aging: A comprehensive study. Analytica Chimica Acta. 530:238-254.
- Anli, R.E., and O.A. Cavuldak. 2013. A review of microoxygenation application in wine. J. Inst. Brew. 118:368-385.
- Asenstorfer, R.E., A.J. Markides, P.G. Iland, and G.P. Jones. 2003. Formation of vitisin A during red wine fermentation and maturation. Australian Journal of Grape and Wine Research. 9:40-46.