Increasing the Efficiency and Accuracy of Labile Cu Measurement in Wine with Screen-Printed Electrodes

Suppression of reductive characters in white wine by Cu fractions: Efficiency and duration of protection during bottle aging

Cu in wine can suppress sulfidic-odours, but the active forms and duration of protection are uncertain. Additions of 0, 0.3 or 0.6 mg/L Cu(II) were made to Chardonnay and Pinot Grigio at bottling. Throughout a 12- or 14-month storage period, Cu fractions were determined by colorimetry, and sulfhydryl compounds by gas chromatography with sulfur chemiluminescence detection. After Cu(II) addition, the dominant Cu fractions were associated with Cu(II)-organic acids (fraction I) and Cu(I)-thiol complexes (fraction II), and over 8-months their concentrations gradually fell below 0.015 mg/L. During this time, a fraction of Cu, predominantly attributed to sulfide-bound Cu, increased in concentration. Suppression of free hydrogen sulfide was assured when the combined Cu fractions I and II concentrations were above 0.015 mg/L, while free methanethiol suppression required Cu fraction I concentration above 0.035 mg/L. Decay rates for Cu fractions demonstrated that the duration that Cu can actively suppress sulfidic odours is wine-dependent.

The removal of Cu from wine by copolymer PVI/PVP: Impact on Cu fractions and binding agents

Specific forms of Cu in wine can influence wine flavour and development. The co-polymer polyvinylimidazole/polyvinylpyrrolidone (PVI/PVP) is known to remove Cu from wine, but its impact on different Cu forms is uncertain. In this study, three Cu fractions in white wine were determined by colorimetry and two Cu fractions in red wine were determined by diatomaceous earth depth filtration and atomic spectroscopy. PVI/PVP, with either silica or chitosan formulations, reduced all three fractions of Cu measured in white wines, and sulfide-bound Cu in red wines. The inefficient removal of organic acid-bound Cu in red wines was linked to the higher pH of red wines. After PVI/PVP treatment, wines showed lower concentrations of hydrogen sulfide, but minimal changes in weaker Cu binding agents. These results demonstrate that PVI/PVP efficiently removes the least desirable form of Cu present in wine, along with its detrimental binding agent (i.e., hydrogen sulfide).

Sulfide-binding to Cu(II) in wine: Impact on oxygen consumption rates

This study investigates the relationship between the two main forms of Cu in wine and their impact on the rate of oxygen consumption. The Cu forms were differentiated by medium exchange constant current stripping potentiometry, which classified the Cu as either bound to sulfide or not. Oxygen consumption rates were determined in red, white and model wines after saturation with oxygen. The results for white wines showed that the oxygen consumption was sensitive to the non-sulfide-bound Cu concentration when ascorbic acid was present, and the first order rates ranged from 0.02 to 0.11 h^-1. However, the same was not true for wines without added ascorbic acid that showed little influence of Cu form on oxygen decay rates. Cu forms were also found to significantly change in some wines during the oxygen decay experiment. Ascorbic acid is critical in enabling the form of Cu to significantly influence the oxygen reaction rate in wine.