Role of Polyphenols in Copper Complexation in Red Wines

Abstract

Four monovarietal red wines, Tinta Roriz, Tinta Barroca, Touriga Nacional, and Touriga Francesa, were studied for their complexometric properties toward copper. For the purpose, ion selective electrode potentiometric titrations were carried out, and the data were treated by two methods suitable for heterogeneous ligands: the Scatchard plot, which provided the complexation capacity (CC(total) = maximum number of moles of sites per liter), and the differential equilibrium function (DEF), which provided the conditional stability constants of the sites effectively involved in the metal complexation (K(DEF)) at a given titration point. The different wines displayed similar properties: CC(total) ranged from 4.5x10(-3) (Tinta Barroca) to 4.9x10(-3) M (Touriga Francesa), and log K(DEF) values were between 4.2 and 6.5. The range of log(|Cu|(bound)/CC(total)) = log theta embraced in the titration was between -0.2 and -1.9. With regard to the natural levels of copper, from 4.4x10(-7) (Tinta Roriz) to 1.3x10(-6) M (Touriga Nacional), and ligands (CC(total)) in the wines, it can be expected that copper will be strongly complexed in the studied wines (log K(DEF) > 6). Studies carried out, in parallel, for solutions of isolated seed tannins and skin polyphenols (mainly anthocyans) showed that their contribution to the CC(total) of the wines was <40% for tannins and <2% for skin polyphenols. However, skin polyphenols were shown to be much stronger copper ligands (log K(DEF) = 6.7, log theta = -1.5) than tannins (log K(DEF) = 4.5, log theta = -1.5).

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

“…With respect to conditional stability constants (Table 2), Vasconcelos et al have reported similar values for Cu with natural ligands in wine [18], although their experimental calculations for total ligand concentrations notably differ from our results. In our opinion this is a very remarkable fact, for it shows that affinity of the metal for natural wine ligands is similar in different varieties but concentration of complexing ligand may vary from one to another.…”

“…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 Effect of Copper Ions on Colour in Extracts of Cabernet Sauvignon and Sangiovese Skins Under Wine-like Conditions

“…However, the ability to form such complexes is related to an ortho-dihydroxyl arrangement on the B ring, so that, while cyanidin, delphinidin and petunidin can form them, those of malvidin, pelargonidin and peonidin cannot. The role of polyphenols has been demonstrated in copper complexation in red wines (Vasconcelos et al, 1999) and, since malvidin-3-O-glucoside is the major anthocyanin in most vinifera grapes, its role in the colour of wines is not considered significant (Boulton, 2001).…”

Physiological responses of Matricaria chamomilla to cadmium and copper excess

“…with peroxidases, is well established (Sgherri et al, 2003). Moreover, phenolics can chelate metals (Vasconcelos et al, 1999). Phenylalanine ammonia-lyase (PAL, EC.…”