The phenolic chemistry and spectrochemistry of red sweet wine-making and oak-aging M. Figueiredo-González a , B. Cancho-Grande a , J. Simal-Gándara a,⇑ , N. Teixeira b , N. Mateus b , V. De Freitas b a Nutrition and Bromatology Group, Analytical and Food Chemistry Department, Faculty of Food Science and Technology, University of Vigo, Ourense Campus, E-32004 Ourense, Spain b Centro de Investigação em Quı ´mica, Departamento de Quı ´mica e Bioquı ´mica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal article info Article history: Received 9 October 2013 Received in revised form 26 November 2013 Accepted 3 December 2013 Available online 9 December 2013 Keywords: Sweet wines Naturally grape dehydration process Fortification with spirits Aging Vitis vinifera L. cv Garnacha Tintorera Phenolic content Proanthocyanidins HPLC abstract A natural sweet wine (NSW) was made with dried grapes from Vitis vinifera L. cv Garnacha Tintorera. A fortified sweet wine (FSW) was also obtained: the maceration-alcoholic fermentation of Garnacha Tinto- rera must was stopped by addition of ethanol 96% (v/v). UV/Vis spectrophotometry and HPLC/DAD-ESI/ MS were applied to determine, respectively, the evolution of colour and phenolic compounds in Garnacha Tintorera based-sweet wines during aging. In sweet wines, aging decreased a / (red/green), colour satura- tion and lightness and increased b / (yellow/blue), and hue angle. Most of the phenolic compounds deter- mined, such as anthocyanins, esters of hydroxycinnamic acids, flavan-3-ols monomers, oligomers and polymers decreased in both sweet wines during aging. On the contrary, hydroxybenzoic and hydroxycin- namic acids and vitisins increased after one year of aging. Despite that both terminal and extension sub- unit compositions show very small changes, mean degree of polymerisation of proanthocyanidins decline slightly as aging progressed in both sweet wines. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Sweet wines are traditionally elaborated in Galicia (the N.W. corner of Spain). The Denomination of Origin (DO) Valdeorras, one of the five DOs in Galicia, wants to promote the production and marketing of new sweet wines. The following red wines were examined in this work. The first one, a naturally sweet wine (NSW) was made with dried grapes Vitis vinifera L. cv Garnacha Tintorera; this cultivar is a teinturier variety which has excellent potential to produce wines from raisined grapes. The second one, a fortified sweet wine (FSW); the maceration-alcoholic fermentation of Garnacha Tintorera must was stopped by addition of ethanol 96% (v/v). Additionally, both sweet wines were subjected to aging process in French oak barrels. The colour changes during wine maturation are usually attrib- uted to anthocyanin polymerisation reactions with other phenolic compounds, such as flavan-3-ol monomers. The formation of these polymeric pigments by direct and/or mediated by acetaldehyde reactions can usually lead to the loss of colouring matter if the polymerised pigments reach high molecular weight (Alañón et al., 2013). The cycloaddition process between anthocyanins and some yeast metabolites such as vinylphenol, pyruvic acid, acetaldehyde leading to more stable pigments, structurally allied to pyranoanthocyanins, is described as other type of reactions established in wines (Atanasova, Fulcrand, Cheynier, & Moutounet, 2002). The formation of these pigments remains in solution and therefore they hardly are lost in the precipitates of colouring mat- ter. Recently, it has been detected the formation of hydroxyphenyl- pyranoanthocyanins such as pinotin A in wines during the aging process (Rentzsch, Schwarz, Winterhalter, & Hermosín-Gutiérrez, 2007). Instead, Oliveira, De Freitas, Silva, and Mateus (2007) de- tected a new class of blue anthocyanin-derived pigments isolated from Port wines, namely portisins (formed from anthocyanins– pyruvic acid adducts and vinyl phenols) and a new family of tur- quoise blue anthocyanin-derived pigments (Oliveira et al., 2010). The physical and chemical characteristics of wood are also important quality factors in the wine aging process, since they af- fect the wood-wine interaction phenomena, such as oxygen-diffu- sion, compound extraction from wood, and oxidation processes in wines (Hernández, Estrella, Dueñas, De Simón, & Cadahía, 2007). Although the quality of sweet wine is determined essentially by aroma compounds, colour and phenolic compounds are also signif- icant sensory attribute of wines. The preservation of the optimal chromatic characteristics during the aging process is the main problem of this type of dessert wine, more than the maintenance of aromatic compounds. Therefore, evolution of colour and pheno- lic compounds during aging process was established in Pedro 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.12.018 ⇑ Corresponding author. E-mail address: jsimal@uvigo.es (J. Simal-Gándara). Food Chemistry 152 (2014) 522–530 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem