Oxidation Management of White Wines Using Cyclic Voltammetry and Multivariate Process Monitoring RUI C. MARTINS, † RAQUEL OLIVEIRA, ‡ FATIMA BENTO, ‡ DULCE GERALDO, ‡ VITOR V. LOPES, § PAULA GUEDES DE PINHO, | CARLA M. OLIVEIRA, ⊥ AND ANTONIO C. SILVA FERREIRA* ,⊥ BioInformatics - Molecular and Environmental Research Center, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal, Departamento de Quı ´mica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal, Laseeb Research Group, Institute for Systems and Robotics, IST, Lisboa, Portugal, REQUIMTE/Departamento de Toxicologia, Faculdade de Farma ´cia da Universidade do Porto, R. Anı ´bal Cunha 164, 4050-047 Porto, Portugal, and Escola Superior de Biotecnologia, Universidade Cato ´lica Portuguesa, Rua Dr. Anto ´nio Bernardino de Almeida, 4200-072 Porto, Portugal The development of a fingerprinting strategy capable to evaluate the “oxidation status” of white wines based on cyclic voltammetry is proposed here. It is known that the levels of specific antioxidants and redox mechanisms may be evaluated by cyclic voltammetry. This electrochemical technique was applied on two sets of samples. One group was composed of normal aged white wines and a second group obtained from a white wine forced aging protocol with different oxygen, SO 2 , pH, and temperature regimens. A study of antioxidant additions, namely ascorbic acid, was also made in order to establish a statistical link between voltammogram fingerprints and chemical antioxidant substances. It was observed that the oxidation curve presented typical features, which enables sample discrimination according to age, oxygen consumption, and antioxidant additions. In fact, it was possible to place the results into four significant orthogonal directions, compressing 99.8% of nonrandom features. Attempts were made to make voltammogram fingerprinting a tool for monitoring oxidation management. For this purpose, a supervised multivariate control chart was developed using a control sample as reference. When white wines are plotted onto the chart, it is possible to monitor the oxidation status and to diagnose the effects of oxygen regimes and antioxidant activity. Finally, quantification of substances implicated in the oxidation process as reagents (antioxidants) and products (off-flavors) was tried using a supervised algorithmic the partial least square regression analysis. Good correlations (r > 0.93) were observed for ascorbic acid, Folin-Ciocalteu index, total SO 2 , methional, and phenylacetaldehyde. These results show that cyclic voltammetry fingerprinting can be used to monitor and diagnose the effects of wine oxidation. KEYWORDS: White wine; antioxidants; cyclic voltammetry; multivariate process INTRODUCTION Oxygen management is one of the most challenging tasks in winemaking. Starting from the grape juice to the maturation process, several critical steps, relating to oxygen exposure, can be found, where the quantities of oxygen supplied will have a major impact on the organoleptic characteristics of the finished wine. In previous work it has been demonstrated that phenylac- etaldehyde, 3-(methylthio)propionaldehyde (methional), and 3-hydroxy-4,5-dimethyl-2(H)furanone (sotolon) play a critical role in the perceived oxidized character of wine (1, 2). Several mechanisms may explain their formation, but it has been demonstrated that temperature and mainly oxygen at lower pH are synergistic (3). Nevertheless, the chemistry of highly electrophilic species presents some particularities. Molecular oxygen (triplet state) needs to be activated to the singlet state to become reactive and then be reduced to water, taking electrons in a stepwise manner (4). In wines, this process requires reducing species with a cathecol-like structure and most important, the presence of transition metal ions, iron or copper, which will act as electron “pumps” during the entire mechanism (4). The reactivity of oxygen species (ROS) increases dramati- cally, constituting an escalating risk toward wine instability, from molecular oxygen (singlet state), perhydroxyl radicals, and hydrogen peroxide to the most destructive hydroxyl radical (4). * Corresponding author: acferreira@esb.ucp.pt. † BioInformatics - Molecular and Environmental Research Center, Universidade do Minho. ‡ Departamento de Quı ´mica, Universidade do Minho. § IST. | Universidade do Porto. ⊥ Universidade Cato ´lica Portuguesa. 12092 J. Agric. Food Chem. 2008, 56, 12092–12098 10.1021/jf8021628 CCC: $40.75  2008 American Chemical Society Published on Web 11/19/2008