Copigmentation of Malvidin-3-O-Monoglucoside by Oenological Tannins: Incidence on Wine Model Color in Function of Botanical Origin, pH and Ethanol Content.

Adeline Vignault,Olga Pascual,Jordi Gombau,Joan Miquel Canals,Pierre-Louis Teissedre,Virginie Moine,Michael Jourdes,Fernando Zamora

doi:10.3390/molecules24081448

Abstract

The effect of the botanical origin, pH level and ethanol content of different oenological tannins on the color of malvidin-3-O-monoglucoside solution, including their effectiveness as copigments, was studied. Briefly, a model wine solution (4 g/L of tartaric acid, pH 3.5 and 12% ethanol) containing 50 mg/L of malvidin-3-O-monoglucoside was prepared and supplemented with 0.1, 0.2 and 0.4 g/L of commercial tannins using (−)-epicatechin as reference control copigment. Six additional model wine solutions (12% ethanol at pH 3.1, 3.5 or 3.9, and 10%, 12% or 14% ethanol at pH 3.5) were prepared as previously described. Samples were stored under airtight conditions. After a week the full absorbance spectrum in the visible range (400–800 nm) was measured and CIELAB color space was determined. These measurements, including an increase in a* (redness), a decrease in b* (yellowness) and a decrease in L* (lightness), indicated that all oenological tannins had a clear positive effect on color copigmentation. Moreover, hydrolysable tannins appeared to be better copigments than condensed tannins as the copigmentation effectiveness (Cp) was found to be between two to four times higher. The effects of these tannins were dose-dependent because a higher addition resulted in a greater impact on copigmentation. In general, an increase in pH and ethanol content resulted in a decrease of the effect of tannins on color. Independent of intrinsic wine conditions, hydrolysable tannins, more specifically gallotannin, remain the most effective in increasing red wine color. These results prove that supplementation with oenological tannins, especially hydrolysable tannins, could be an interesting tool for the improvement of the red wine color.

Highlights

Anthocyanins, are the main compounds responsible for the color of red wines
Anthocyanins can form association structures with other colorless compounds, with other anthocyanins, or in the case of coumaroylated and caffeoylated anthocyanins, the acylated esterified group can associate with the pyrylium ring of the anthocyanidin [7,8]
Some differences can be noted between tannins from the same botanical origin, but in the majority of the cases, no significant differences were noted between tannins of the same family

Summary

Introduction

Anthocyanins, are the main compounds responsible for the color of red wines. They are the major natural pigments in red wines, reaching typically 500 mg/L in young red wines [1], but their concentration depends on the grape variety and the growing conditions [2]. Molecules 2019, 24, 1448 cyanidin-3-O-glucoside, delphinidin-3-O-glucoside, pelargodinin-3-O-glucoside, peonidin-3-O-glucoside and petunidin-3-O-glucoside [3,4] These anthocyanins are present in acylated forms with acetic, coumaric and caffeic acids [5]. The extraction and formation of new pigments or copigment complexes permit the color stabilization of red wine during the aging process since the monomeric anthocyanin content decreases constantly. The copigmentation phenomenon is characterized by the formation of a “sandwich complex,” meaning a hydrophobic interaction (π–π stacking) between the B ring of the anthocyanin and the copigment (phenolic compounds, for example) [7]

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