Composition and evolution of oligomeric proanthocyanidin-malvidin glycoside adducts in commercial red wines

Quantitative and qualitative composition of proanthocyanidins and other polyphenols in commercial red wines and their contribution to sensorially evaluated tannicity

The analysis of proanthocyanidins (PA) in red wine has typically been conducted using few key methods, such as phloroglucinolysis or precipitation assays. Here, the content of PAs and other common polyphenol groups in commercial red wines were analyzed with a group-specific liquid chromatography-tandem mass spectrometry method. Besides concentrations, the method provides qualitative information about the detected compound groups in the form of two-dimensional (2D) chromatographic fingerprints. The 2D fingerprints of PAs have not been utilized in analysis of red wine before. For instance, 2D chromatographic fingerprints revealed that the complex PA compositions were qualitatively notably similar between many wine types, even when there were considerable differences in concentrations. Finally, 201 commercial red wines had been categorized as either tannic or medium tannic based on their sensorial evaluations. The content of PAs and three different groups of oligomeric adducts of malvidin glycosides and PAs were measured from these wines. The compositional features of the PAs and PA-malvidin glycoside adducts were more important than concentrations in explaining the perceived tannicity.

Liquid Chromatography-Mass Spectrometry-Based Metabolomics for Understanding the Compositional Changes Induced by Oxidative or Anoxic Storage of Red Wines

The aim of this work was to study the physicochemical changes of eight red wines stored under conditions differing in O₂ exposure and temperature and time under anoxia. The methods used to analyze the wines included the measurement of volatile sulfur compounds, color, tannin (T) polymerization, and liquid chromatography-mass spectrometry untargeted metabolomic fingerprint. After 3 months, the color of the oxidized samples evolved 4-5 times more intensively than in wines stored under anoxia. The major metabolomic differences between oxidative and anoxic conditions were linked to reactions of acetaldehyde (favored in oxidative) and SO₂ (favored in anoxia). In the presence of oxygen, the C-4 carbocation of flavanols delivered ethyl-linked tannin-anthocyanin (T-A) and tannin-tannin (T-T) adducts, pyranoanthocyanins, and sulfonated indoles, while under reduction, the C-4 carbocation delivered direct linked T-A adducts, rearranged T-T adducts, and sulfonated tannins. Some of these last reactions could be related to the accumulation of reduced species, eventually ending with reductive off-odors.