Cu In Wine Research Articles

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.

Sulfide-bound copper removal from red and white wine using membrane and depth filters: Impacts of oxygen, H2S-to-Cu ratios, diatomaceous earth and wine volume

Sulfide-bound Cu in wine is a potential contributor to the reductive development of wine. This study examines the effectiveness of filtration for the adsorptive removal of this Cu fraction. The copper concentration in wine before and after filtration was determined by atomic spectroscopy (total) and by stripping potentiometry and/or adsorptive methodologies (Cu fractions). Membrane filters (4.7 cm2) removed significant amounts of sulfide-bound Cu from 10 mL of wine, including 60–80 % removal using nylon membranes, but they could not efficiently remove Cu from larger volumes. Dissolved oxygen concentration in the wine immediately prior to membrane filtration did not impact Cu removal, while a high sulfide-to-Cu(II) ratio did enhance removal. Depth filters incorporating diatomaceous earth with cellulose (45 mm-diameter, 3.5 mm-thickness) showed the most efficient removal of sulfide-bound Cu from wines even after treatment of 3.0 L. The relevance of these laboratory scale filtrations to winery scale filtration is discussed.

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).

Simplified measures of copper fractions in wine: colorimetric and filtration‐based approaches

Background and Aims Simple methods for determining Cu forms in wine do not currently exist. This study demonstrates the relevance of measuring a specific fraction of Cu in wine, and introduces simplified methods for its measurement utilising either colorimetry, or filtration in combination with routine measures of total Cu in wine. Methods and Results Electrochemically detectable Cu provided a threshold level of Cu that related directly to the accumulation of free hydrogen sulfide and free methanethiol in bottled wines. A simple colorimetric method using bicinchoninic acid was optimised to allow a rapid approximation of this fraction of Cu in white wine. By modification of the measurement conditions, an extra fraction of Cu associated with the partial release of Cu from thiols could also be quantified. The use of diatomaceous earth depth filters to isolate these fractions of Cu was also assessed. After passing red wine through the filters, the concentration of Cu in the filtrate correlated well with the electrochemically detectable Cu. Alternatively, for white wine the concentration of filtrate Cu overestimated this fraction of Cu and this was attributed to its inability to distinguish sulfhydryl-free Cu from Cu loosely bound to thiols. Conclusions Multiple and simplified approaches have been devised to allow measurement of Cu fractions in wine. Significance of the Study These methodologies will allow an important fraction of Cu in wine to be measured with a spectrophotometer.

The colorimetric determination of copper in wine: total copper

Background and Aims The total concentration of copper (Cu) in wine cannot be routinely measured without relatively expensive equipment, reagents and/or without labour‐intensive sample pretreatment. The following research describes an approach for the colorimetric measurement of total Cu in wine utilising a spectrophotometer and relatively cheap reagents. Method and Results The proposed method is based on using bicinchoninic acid as the complexing chromophore for Cu. Copper was measured directly and rapidly in white wine, while a digestion of red wine was required. A key step for the analysis in the non‐digested white wine matrix was the addition of silver(I) to aid the dissociation of Cu in the wine from sulfide. For red and white wines, the limit of detection was 0.02 mg/L Cu, and the repeatability was 3 ± 1%. The accuracy of the method was assessed in terms of recovery experiments (102 ± 3%, n = 4), and also by comparing total Cu concentration in 84 wines determined by the colorimetric method with that obtained by inductively coupled plasma with optical emission spectroscopy (R2 = 0.95). Conclusions The colorimetric determination of total Cu was successfully optimised and validated in white and red wines. Significance of the Study The methodology will allow wineries and researchers to routinely measure total Cu concentration in wine with a spectrophotometer.

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.

Direct Determination of Zn, Cd, Pb and Cu in Wine by Differential Pulse Anodic Stripping Voltammetry

Metals in wine can originate from natural and anthropogenic sources and their concentrations have significant effects on wine proprieties as well in its conservation. In this work, direct and simultaneous determinations of Zn, Cd, Pb and Cu in wine samples were carried out by differential pulse anodic stripping voltammetry without any steps of previous pretreatment. The samples analyzed presented concentration levels from 4.64 to 69.3 µg L−1 of Zn, from 1.74 to 5.25 µg L−1 of Cd, from 4.57 to 17.9 µg L−1 of Pb and from 1.0 to 10.3 µg L−1 of Cu. Accuracy was evaluated with the standard addition method and recoveries ranged from 82.5 and 130.8% for Zn, from 85.7 to 107.0% for Cd, from 89.7 to 101.0% for Pb and from 81.4 to 105.9% for Cu. With the application of this method, it was possible to quantify the metals in a simple and easy way not requiring sample preparation or other approaches for the destruction of organic substances.

Chemistry of Manganese and Interaction with Iron and Copper in Wine

Iron (Fe) plays a key role in wine oxidation. The reduction potential of the Fe(III)/Fe(II) redox couple in wine conditions allows Fe(II) to react with O2 and Fe(III) to react with polyphenols with the assistance of sulfite. Copper (Cu) accelerates Fe(II) oxidation and thus can greatly accelerate wine oxidation. Some studies suggest that manganese (Mn), which is present at concentrations similar to those of Fe in wine, may also participate in the catalytic process. This study was therefore undertaken to examine the possible interaction of Mn with Fe and Cu in wine. The reduction potential of the Mn(III)/Mn(II) redox couple is considerably higher than that of the Fe couple. As a result, Fe(III), H2O2, and O2 cannot oxidize Mn(II). Furthermore, Mn(III) is a stronger oxidant than Fe(III) and rapidly oxidizes tartaric acid. Thus, Mn cannot redox-cycle in the same way as the Fe couple. Despite this, Mn(II) accelerates Fe(II) oxidation in an air-saturated wine model, and it is proposed that Mn(II) reacts with an intermediate Fe(III)-superoxo complex to generate Mn(III). This accelerates the oxidation of 4-methylcatechol (4-MeC; a model polyphenol) in the presence of Fe and Cu in the model wine. Mn is a powerful catalyst of sulfite autoxidation, involving a radical chain reaction initiated by traces of Fe. As a radical scavenger, 4-MeC prevents chain propagation and, as with Fe, polyphenols prevent Mn-catalyzed sulfite autoxidation in wine. Results show that Mn accelerates the air oxidation of white wine, which is most evident at high Fe and Cu concentrations.

Square-wave anodic-stripping voltammetric determination of Cd, Pb and Cu in wine: Set-up and optimization of sample pre-treatment and instrumental parameters

For the first time, square-wave anodic-stripping voltammetry (SWASV) was set up and optimized for the determination of Cd, Pb and Cu in white wine after UV photo-oxidative digestion of the sample. The best procedure for the sample pre-treatment consisted in a 6-h UV irradiation of diluted, acidified wine, with the addition of ultrapure H2O2 (three sequential additions during the irradiation). Due to metal concentration differences, separate measurements were carried out for Cd (deposition potential −950mV vs. Ag/AgCl/3M KCl deposition time 15min) and simultaneously for Pb and Cu (Ed −750mV, td 30s). The optimum set-up of the main instrumental parameters, evaluated also in terms of the signal-to-noise ratio, were as follows: ESW 20mV, f 100Hz, ΔEstep 8mV, tstep 100ms, twait 60ms, tdelay 2ms, tmeas 3ms. The electrochemical behaviour was reversible bielectronic for Cd and Pb, and kinetically controlled monoelectronic for Cu. Good accuracy was found both when the recovery procedure was used and when the results were compared with data obtained by differential pulse anodic stripping voltammetry. The linearity of the response was verified up to ∼4μgL−1 for Cd and Pb and ∼15μgL−1 for Cu. The detection limits for td=5min in the 10 times diluted, UV digested sample were (ngL−1): Cd 7.0, Pb 1.2 and Cu 6.6, which are well below currently applied methods. Application to a Verdicchio dei Castelli di Jesi white wine revealed concentration levels of Cd ∼0.2, Pb ∼10, Cu ∼30μgL−1 with repeatabilities of (±RSD%) Cd ±6%, Pb ±5%, Cu ±10%.

Active Versus Laddered Municipal Bond Portfolio Management

Iron plays a key role in wine oxidation. The reduction potential of the Fe(III)/Fe(II) redox couple in wine conditions allows Fe(II) to react with O₂, and Fe(III) to react with polyphenols with the assistance of sulfite. Cu accelerates Fe(II) oxidation and so can greatly accelerate wine oxidation. Some studies suggest that Mn, which is present at similar concentrations to Fe in wine, may also participate in the catalytic process. This study was therefore undertaken to examine the possible interaction of Mn with Fe and Cu in wine. The reduction potential of the Mn(III)/Mn(II) redox couple is considerably higher than that of the Fe couple. As a result it is shown that Fe(III), H₂O₂ and also O₂ cannot oxidize Mn(II). Furthermore Mn(III) is a much stronger oxidant than Fe(III) and rapidly oxidizes tartaric acid. It is immediately apparent, therefore, that Mn cannot redox-cycle in the same way as the Fe couple. Despite this unpromising profile, Mn(II) is shown to accelerate Fe(II) oxidation in air saturated model wine and it is proposed that it reacts with an intermediate Fe(III)-superoxo complex to generate Mn(III). As a result it accelerates the oxidation of 4-methylcatechol (4-MeC, a model polyphenol) in the presence of Fe and Cu in model wine. Mn is a powerful catalyst of sulfite autoxidation, involving a radical chain reaction initiated by traces of Fe. As a radical scavenger, 4-MeC prevents chain propagation and so, as with Fe, polyphenols prevent Mn catalysed sulfite autoxidation in wine. Mn is shown to accelerate the air oxidation of a white wine, which is most evident with high Fe and Cu levels.