Evolution of metal and polyphenol content over a 1-year period of vinification: sample fractionation and correlation between metals and anthocyanins

Complexing capacity profiles of naturally occurring ligands in Tempranillo wines for Cu and Zn

“…As a matter of fact, a rapid increase in polyphenols and anthocyanins concentration was found in the early three or four days of fermentation as reported elsewhere for wine prepared from same variety grapes collected at the same spot in the previous vintage (2002), reaching a tableau for longer fermentation days [13]. Thus, DPASV appears to be an efficient and extremely sensitive tool to detect the diverse complexing-adsorption patterns onto the mercury electrode.…”

“…Commercial wines were microwaved as such, whereas samples under vinification were previously centrifuged in order to separate dregs from supernatants by using a Biofuge Stratus (Heraeus) centrifuge, at 4ºC ; 6 mL sub boiling (s.b.) HNO 3 was added to each 2 mL supernatant sample before proceeding to the microwave assisted digestion routine, that was identical to that published elsewhere [13]. Once digested, all samples were taken to 10 mL volume with ultra-pure water.…”

“…Preliminary studies showed that all of them adjusted fairly well to a 1:1 stoichiometry. Since cyanidin is one of the most abundant polyphenols in wine and -most of all-since it is the only one that was found to closely correlate with metals in the fractionation of a wine sample [13], further attention was paid to its complexing capacity with respect to Cu. Brouillard et al [34] have reported that at pH 4 at least four molecular forms may be found in equilibrium, namely, carbinol (49.4%), chalcone (30,1%), quinone (16.3%) and flavilio form (4.2%); the latter form was not considered given its low percentage at the working pH [35].…”

“…Zn and Cu have both been chromatographically found to specifically associate to cyanydin-3-glucoside which is one of the most abundant anthocyanins in red wines [13] and their complexing capability with individual polyphenols in different media has been electrochemically evaluated [14][15][16][17]. Presence of metals accompanying natural ligands in commercial wines comes as a result of their mutual interaction along winemaking where metals intervene in multiple processes such as complex formation [18], polymerization, flocculation and precipitation [6,10,19].…”

“…Presence of metals accompanying natural ligands in commercial wines comes as a result of their mutual interaction along winemaking where metals intervene in multiple processes such as complex formation [18], polymerization, flocculation and precipitation [6,10,19]. Besides, Zn concentration remains more or less constant along vinification, while Cu profile shows a decreasing tendency [13,20]. The above described distinct behaviour could be an expression of a different complexing pattern for both metals which we have tried to clarify through their well known electrochemical stripping response.…”