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Oenological Tannins : characteristics, properties and functionalities. Impact on wine quality.

Abstract : The use of oenological tannins is a common practice worldwide in winemaking. However, up to date this use, is only authorized by the OIV to facilitate wines and must clarification. Nevertheless, oenological tannins are used for several reasons, explaining the existence of diverse tannins on the market. For all these reasons, OIV has begun few years ago to create a working group in order to conduct a large study on oenological tannins. Thus, the aim of this research was to carry out an exhaustive study to determine firstly the chemical composition and the richness in tannins of the oenological tannins. Secondly, their potential functionalities were studied, focusing on their antioxidant activity, their ability to stabilize and improve wine color and finally, their antioxidasic activity. Concerning chemical composition, the principal tannins monomers, dimers, trimers and tetramers were identified and quantified by HPLC-MS and LC-QTOF. The abundance in tannins was estimated by different methods: TPI, Bate-Smith, Methyl-cellulose, Folin-Ciocalteu, OIV official method and phloroglucinolisis. The antioxidant capacity was measured 5 methods (ABTS, CUPRAC, DPPH, FRAP and ORAC) meanwhile the oxygen consumption was measured using a non-invasive method based on luminescence. Antioxidasic property, was achieved by measuring first the laccase activity in winemaking, then by determined inhibition type and finally by laccase characterization precipitation by electrophoresis SDS-PAGE. The oenological tannins ability to stabilize the color was determined by their bathochromic and hyperchromic effect and by the calculation of the copigmentation index. Their color stabilization effect was evaluated during several days, different ethanol content and pH level. The results confirm that oenological tannins and specifically, ellagitannins, really protect wine against oxidation either because they exert antioxidant capacity and/or they consume directly oxygen. Moreover, oenological tannins can improve and stabilize red wines color acting as copigments, with gallotannins being the most efficient ones. In addition, oenological tannins, particularly grapes tannins, can be a new tool to inhibit the laccases produced by B. cinerea. As a fruit of these results, the OIV resolutions OENO-TECHNO 17-612 and OENO-TECHNO 17-613, just accepted, proposed to include two new functionalities of tannins uses in musts and wines:•Contribute to the antioxidant protection of must and wine components•Promote the expression, stabilization and preservation of color.
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Adeline Vignault. Oenological Tannins : characteristics, properties and functionalities. Impact on wine quality.. Agricultural sciences. Université de Bordeaux; Universitat Rovira i Virgili (Tarragone, Espagne), 2019. English. ⟨NNT : 2019BORD0263⟩. ⟨tel-02499650⟩

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