Improving the Phloroglucinolysis Protocol and Characterization of Sagrantino Wines Proanthocyanidins.

Panagiotis Arapitsas,Fulvio Mattivi,Daniele Perenzoni,Graziano Guella

doi:10.3390/molecules26041087

Abstract

Proanthocyanidins are key metabolites that explain wine sensorial character (bitterness and astringency) and red wine color changes during aging. Therefore, a fast and accurate method to evaluate the degree of polymerization and the structural composition of the polymeric proanthocyanidins is a crucial analytical tool. Phloroglucinolysis is the most used method for this analysis but, unfortunately, the phloroglucinol adducts of the monomeric flavan-3-ols are not commercially available, making the results less accurate. The aim of this work was the isolation by semi-preparative high performance liquid chromatography (HPLC) of these non-commercial compounds and their use for the development of an accurate UHPLC-MS/MS protocol. The purity of each adduct was established via quantitative 1H-nuclear magnetic resonance (NMR) measurements with 3-trimethylsilyl-propionic-d4 acid sodium salt as the calibration standard. The developed method was applied to evaluate the proanthocyanidins profile of Sagrantino di Montefalco wines in comparison to other well-known tannic wines. Commercial, 6–8 years old Sagrantino wines were demonstrated to be very rich in epicatechin type B procyanidins, to have low galloylation %, and to have a high mean degree of polymerization of the proanthocyanidins with respect to the other analyzed wines.

Highlights

Proanthocyanidins or condensed tannins is a group of secondary metabolites of paramount importance since they have a great impact on human health and food quality [1,2,3]
While the trapping reagent 2-mercaptoethanol has been widely used in the past, the protocols based on the acidic cleavage in the presence of phloroglucinol, followed by an LC-MS analysis are the most commonly used in the last years [7,18,19,20,21,22,23,24,25,26,27], especially when the desired target is the maximal conversion of proanthocyanidins into their constitutive subunit adducts [28]
The use of a semipreparative chromatography system allowed the isolation of epicatechin 4-phloroglucinol (EP-Phl) (Figure 3)

Summary

Introduction

Proanthocyanidins or condensed tannins is a group of secondary metabolites of paramount importance since they have a great impact on human health and food quality [1,2,3]. They can be found in large amounts in the majority of fruits, vegetables and plants, like wine, tea, berries, medicinal and aromatic plants and apples. Due to their quasi-ubiquitary presence in our plant food, the human average intake per day is very high in comparison with that of other classes of polyphenols [4,5]. The availability of pure standards of the flavan-3-ol phloroglucinol adducts are required for the quantification of acid-catalyzed phloroglucinol degradation products of procyanidins [29]

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Conclusion