title: Extraction of phenolics in liquid model matrices containing oak chips: Kinetics, liquid chromatography-mass spectroscopy characterisation and association with in vitro antiradical activity.
abstract: Four different liquid model matrices were utilised to study the leaching of polyphenols from oak chips. The matrices included distilled water, 12% (v/v) ethanol, 12% (v/v) ethanol adjusted to pH 3.4, and 55% (v/v) ethanol. Extraction of phenolics into the liquid systems was monitored by the estimation of the total polyphenol concentration, using the Folin-Ciocalteu method. The in vitro antiradical activity was also recorded using the stable DPPH radical, to ascertain enrichment of the solutions with potentially antioxidant compounds. As a final step, the polyphenolic composition of each matrix was characterised by means of liquid chromatography-electrospray ionisation mass spectrometry. The kinetics of polyphenol leaching into the liquid phase was found to obey a 2nd parameter power equation of the type y=ax(b), which produced a good fit of the data (p<0.0001). Kinetics was faster in distilled water up to a point, where after polyphenol extraction occurred at higher rate in the 55% ethanolic solution. The antiradical activity in all cases was highly correlated with total polyphenol concentration (p<0.001), providing that the amount of polyphenols extracted into the liquid media exerted a proportional antioxidant effect. The analytical examination by liquid chromatography-mass spectrometry revealed that the compounds implicated are hydrolysable tannins and hydrolysis products thereof.
authors.affiliation: Ecole National Supérieur Agronomique de Montpellier (E.N.S.A.M.), 2 Place Vialla, 34060 Montpellier Cedex, France.
authors.forename: Evangelia
authors.initials: E
authors.lastname: Karvela
authors.affiliation: Department of Food Quality and Chemistry of Natural Products, Mediterranean Agronomic Institute of Chania (M.A.I.Ch.), P.O. Box 85, 73100 Chania, Greece. Electronic address: dimitris@maich.gr.
authors.forename: Dimitris P
authors.initials: DP
authors.lastname: Makris
authors.affiliation: Department of Food Quality and Chemistry of Natural Products, Mediterranean Agronomic Institute of Chania (M.A.I.Ch.), P.O. Box 85, 73100 Chania, Greece.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Kefalas
authors.affiliation: Ecole National Supérieur Agronomique de Montpellier (E.N.S.A.M.), 2 Place Vialla, 34060 Montpellier Cedex, France; Viticulture-Œnologie, Agro de Montpellier/Insitut National de Résearch Agronomique (I.N.R.A.), 2 Place Vialla, 34060 Montpellier Cedex, France.
authors.forename: Michael
authors.initials: M
authors.lastname: Moutounet
keywords: Antioxidants; Antiradical activity; Hydrolysable tannins; Model systems; Oak chips