PINKING PHENOMENA ON WHITE WINES: RELATION BETWEEN PINKING SUSCEPTIBILITY INDEX (PSI) AND WINE ANTHOCYANINS CONTENT

Abstract

Pinking is the emergence of pink tones in white wines exclusively produced from white grape varieties, known as pinking phenomena for many years. Pinking is essentially appeared when white wines are produced under reducing conditions [1,2,3]. Pinking usually occurs after bottling and storage of white wines, but its appearance has also been described after alcoholic fermentation or even as soon as the grape must is extracted [4]. Therefore, the purpose of this work was to investigate the existence of an-thocyanins in white wines made from different white grape varieties and grown locations and critically evaluate the most common method used for predicting pinking appearance in white wines: the Pinking Susceptibility Index (PSI). Anthocyanins were concentrated by SPE [1]. Also, the products formed by hy-drogen peroxide oxidation of the same wines were isolated using this method. The correlation between the PSI and the whole visible spectra was studied by multivariate statistical methods, PCA and PLS ana-lysis, to evaluate the spectral regions in the visible spectra most important to the measured PSI. No cor-relation between anthocyanins concentration and the Pinking Susceptibility Index (PSI) was observed contrarily to the colour of wines exposed to oxygen (r = 0.871, p < 0.00005) [5]. The oxidation of wines with hydrogen peroxide resulted in the formation of various compounds. PSI was correlated with com-pounds absorbing in the 400–480 nm region, probably more related to the browning than the pinking phenomenon. The lack of correlation between the PSI and anthocyanins concentration in white wines can be due to the different chemical compositions of white wines that yield various compounds after oxidation that might not be related to the natural wine pinking phenomenon. Acknowledgments We appreciate the financial support provided to CQ-VR – Chemistry Research Centre – Vila Real (UIDB/00616/2020 and UIDP/00616/2020) by FCT – Portugal and COMPETE. The financial support of the project AgriFood XXI (NORTE-01-0145-FEDER-000041) co-financed by the European Regional Development Fund through NORTE 2020 (Programa Operacional Regional do Norte 2014/2020) is also acknowledged.