A NEW STRATEGY AND METHODOLOGY FOR THE CHARACTERIZATION OF POLYPHENOLS IN FINING PRECIPITATE

Abstract

Polyphenols are secondary metabolite widely distributed in plant kingdom such as in fruits, in grapes and in wine. During the winemaking process, polyphenols are extract from the skin and seed of the berries. Fining is an important winemaking step just before bottling which has an impact on wine stabi-lization and clarification. Most the time, fining agent are animal or vegetal protein while some of them can be synthetic polymer like PVPP or natural origin like bentonite. The aim of this study was better understand colloidals phenomenons involved in fining process and determine how polyphenols content and composition are impact by finning.

Different type and composition of fining agent were used during the investigation on each wine. Some of them were based on animal proteins, vegetal proteins, PVPP or bentonite alone while some mix with PVPP and vegetal proteins, PVPP and animal protein, and a mix with PVPP, vegetal proteins and bentonite were also used. On the wine before and after fining monomeric and total anthocyanins, monomeric, dimeric and total tannins, mDP (mean degree of polymerization), flavonol and phenolic acids content were measured. However in order to determine more precisely the content and composition of polyphenol lost during fining, a new strategy have been develop based on the re-solubilisation of the fining precipitate using some organic solvent.

For these experiments, this new method highlight some drastic differences between fining agents. Indeed, depending of the fining agent the amount and the composition of the polyphenols present in the fining precipitate change. For example, some fining agent don’t remove anthocyanins while some other precipitate mainly the p-coumarolylated anthocyanins. Moreover, important differences are also observed for condensed tannins according to the nature of the fining agent. Indeed, fining agent without PVPP were able to precipitate monomeric or dimeric condensed tannins. Moreover, some fining agent are more selective of oligomeric tannins while some has tendency to precipitate tannins with higher mDP.

This new methodology allow a more precise and clear identification of the polyphenol precipitated by fining agent and will help to better understand impact of the fining the organoleptic properties of the wine. Similarly, a better characterization of the fining precipitate will also help better understanding the colloidal structure of the wine.