Analytical strategies for the measurement of different forms of Cu and Fe in wine: Comparison between approaches in relation to wine composition.

The speciation of Cu and Fe in wine was assessed by a number of methodologies and those with superior performance were utilised on 49 wines and compared to compositional data. The adopted analytical strategies were stripping potentiometry, HPLC and an extraction (solid-phase or liquid-liquid) followed by atomic absorption or optical emission spectroscopic measurement. Stripping potentiometry was specific for sulfide-bound Cu in wines, and showed that this was the predominant form of Cu.

Exploiting Compositionally Similar Grape Marc Samples to Achieve Gradients of Condensed Tannin and Fatty Acids for Modulating In Vitro Methanogenesis.

Ruminants produce large amounts of the greenhouse gas, methane, which can be reduced by supplementing feed with products that contain anti-methanogenic compounds, such as the solid winemaking by-product, grape marc. The aim of this study was to exploit compositional differences in grape marc to better understand the roles of condensed tannin and fatty acids in altering methanogenesis in a ruminant system. Grape marc samples varying in tannin extractability, tannin size and subunit composition, and fatty acid or tannin concentrations were selected and incubated in rumen fluid using an in vitro batch fermentation approach with a concentrate-based control.

Evaluation of putative precursors of key 'reductive' compounds in wines post-bottling.

Precursors to hydrogen sulfide (HS), methanethiol (MeSH), ethanethiol (EtSH), and dimethyl sulfide (DMS) were assessed in wines post-bottling, and the percent yield of VSCs from each precursor determined. Cysteine (Cys) and glutathione (GSH) were associated with small increases in HS concentrations, with a maximum yield of 0.18% and 1.

The impact of wine components on fractionation of Cu and Fe in model wine systems: Macromolecules, phenolic and sulfur compounds.

A variety of techniques have been developed with the ability to measure different forms of metals in wine with the ultimate aim of providing a more accurate indicator of metal induced spoilage of wine. This study was conducted in order to identify which wine components influence the measurement of Cu and Fe in their fractionated and/or electrochemically active forms. The measurement techniques involved detection of labile Cu by stripping potentiometry and fractionation of Cu and Fe by sequential solid phase extraction, with detection by inductively coupled plasma-optical emission spectroscopy.

Formation of Hydrogen Sulfide in Wine: Interactions between Copper and Sulfur Dioxide.

The combined synergistic effects of copper (Cu(2+)) and sulfur dioxide (SO₂) on the formation of hydrogen sulfide (H₂S) in Verdelho and Shiraz wine samples post-bottling was studied over a 12-month period. The combined treatment of Cu(2+) and SO₂ significantly increased H₂S formation in Verdelho wines samples that were not previously treated with either Cu(2+) or SO₂. The formation of H₂S produced through Cu(2+) mediated reactions was likely either: (a) directly through the interaction of SO₂ with either Cu(2+) or H₂S; or (b) indirectly through the interaction of SO₂ with other wine matrix compounds.

Survey of the Variation in Grape Marc Condensed Tannin Composition and Concentration and Analysis of Key Compositional Factors.

Grape marc contains a number of compounds with potential antimethanogenic activity in ruminants, including condensed tannins (CTs). Using direct phloroglucinolysis, a survey of CT chemistry across 66 grape marc samples showed diversity in concentration (6.9 to 138.

The effects of pH and copper on the formation of volatile sulfur compounds in Chardonnay and Shiraz wines post-bottling.

The effects of pH and Cu(2+) treatment on the formation of volatile sulfur compounds (VSCs) were investigated in Chardonnay and Shiraz wine samples. Four VSCs were significantly affected by pH, with lower wine pH associated with decreased hydrogen sulfide (H2S), methanethiol, dimethyl sulfide, and carbon disulfide concentrations. The effects of pH and Cu(2+) on H2S formation from known precursor compounds were subsequently studied in a model wine system.