Spectroscopy analysis of phenolic and sugar patterns in a food grade chestnut tannin.

Tannin of chestnut (Castanea sativa Mill.) wood, commonly used in winemaking was characterised with a spectroscopy qualitative approach that revealed its phenolic composition: several vibrational diagnostic bands assigned using the Attenuated Total Reflectance-Infrared Spectroscopy, and fragmentation patterns obtained using the Laser-Desorption-Ionization Time-of-Flight technique evidenced polygalloylglucose, e.g. castalagin/vescalagin-like structures as the most representative molecules, together with sugar moieties. The implication of these findings on winemaking application and the potential influence of the chemical structure on the sensory properties of wine are discussed.

A cyclic voltammetry method suitable for characterizing antioxidant properties of wine and wine phenolics.

Phenolic antioxidants are ranked by reducing strength and characterized for reversibility using cyclic voltammetry at a glassy carbon electrode. Phenolics with an ortho-diphenol group show a first oxidation peak close to 400 mV (vs. Ag/AgCl) in a model wine solution (12% ethanol, 0.033 M tartaric acid, adjusted to pH 3.6), with a linear concentration dependence below 0.01 mM. Dilution of white wines 10x, and red wines 400x, gave first oxidation peak currents in the 1.5 to 2.2 microA range and 1.9 to 3.4 microC of charge passed by 500 mV, producing values for the concentrations of phenolic antioxidants with low oxidation potentials in the wines. Further peaks in the cyclic voltammograms of the diluted wines correspond to classes of phenolics with higher oxidation potentials, providing a qualitative assessment of wine phenolics based on reducing strength.

Electrochemical detection of natural antioxidants: principles and protocols.

An overview is provided of the use of cyclic voltammetry and electrochemical detectors for HPLC to characterize antioxidants that are active as reducing agents at inert electrodes. Results are presented for cyclic voltammetry at a glassy carbon electrode in 50% methanol, 50% 0.1 M HClO4, a solution typically used in HPLC separations of natural antioxidants. The relative reducing strength of each antioxidant is estimated by the formal potential, and information is also obtained regarding the reversibility of the oxidation of the antioxidants, and the extent to which the carbon electrode is contaminated by the products of oxidation. Cyclic voltammetry of complex mixtures such as blood serum and wine produces a measure of the total antioxidant status due to antioxidants with a low oxidation potential. The results of cyclic voltammetry studies are relevant to interpreting the performance of carbon electrodes in electrochemical detectors for HPLC.