Automated ABTS Method for the determination of Trolox-Equivalent Antioxidant Capacity (TEAC) of red wine.

The antioxidant capacity of red wines was determined to characterise the wines according to grape variety and geographic origin. The reagent ABTS (2, 2'-azino-di-[3-ethylbenzthiazoline-6-sulphonate]) was incubated with potassium persulphate to produce the radical cation ABTS + . This has a relatively stable blue-green colour and peak absorbance at 750 nm. Antioxidants in wine reduce ABTS + , which lowers the absorbance at 750 nm in proportion to the total antioxidant concentration. The method was validated and automated for an automatic analyser. Each ABTS + determination took approximately six minutes, and a batch of measurements could be run overnight. The relative standard uncertainty of the method was 5.1%. 104 single-variety red wines Cabernet Sauvignon, Gamay, Malbec, Merlot, Pinotage, Pinot Noir, Sangiovese, Syrah, Tannat or Tempranillo) and 15 other red wines were analysed. Total phenols, free and total sulphur dioxide, ethanol, pH, volatile acids, total acids, glucose and fructose, as well as colorimetric parameters such as absorbance at 420 nm, were measured on the samples. Antioxidant capacity showed strong correlation with total phenols and UV280 and moderate correlation with UV420, ethanol and dry extract. General linear models were fitted both to the training and validation data. A model, that was selected based on those analysis, contained Folin C and grape variety as explanatory variables. The R-square of the model, while fitted to the training data, was 0.9090.