Chemical Characterization of Red Wine Polymers and Their Interaction Affinity with Odorants.

In order to characterize red wine polymers with regard to their binding properties to aroma compounds (odorants), a qualitative and quantitative analysis of chemical degradation products after different chemical treatments (thiolytic, acidic, and alkaline depolymerization) of high -molecular-weight (HMW) fractions of red wine was performed. Using 1H NMR, LC-ToF-MS, LC-MS/MS, and HPIC revealed key structural features such as carbohydrates, organic acids, phenolic compounds, anthocyanins, anthocyanidins, amino acids, and flavan-3-ols responsible for odorant-polymer interactions. Further, NMR-based interaction studies of the selected aroma compounds 3-methylbutanol, cis-whisky lactone, 3-methylbutanoic acid, and 3-isobutyl-2-methoxypyrazine with HMW polymers after chemical treatment demonstrated a reduced interaction affinity of the polymer compared to the native HMW fractions, and further, the importance of aromatic compounds such as flavan-3-ols for the formation of odorant polymer interactions. In addition, these observations could be verified by human sensory experiments. For the first time, the combination of a compositional analysis of red wine polymers and NMR-based interaction studies with chemically treated HMW fractions enabled the direct analysis of the correlation of the polymer's structure and its interaction affinity with key odorants in red wine.

Investigating the Role of Odorant-Polymer Interactions in the Aroma Perception of Red Wine: A Density Functional Theory-Based Approach.

The aroma of red wine results from the intricate interplay between aroma compounds (odorants) and complex polymers generated during fermentation. This study combines density functional theory (DFT), human sensory experiments, and nuclear magnetic resonance to investigate the impact of odorant-polymer interactions on wine aroma. Molecular aggregation patterns of odorants with polymer segments are identified, indicating the crucial role of intermolecular noncovalent interactions, such as hydrogen bonds and van der Waals interactions, in stabilizing odorant-polymer conformations. Certain odorants, including 3-isobutyl-2-methoxypyrazine and cis-whisky lactone, exhibit high binding affinity to specific polymer segments, such as (+)-catechin and p-coumaric acid, resulting in substantial changes in the perceived aroma. Their strong binding affinities correlate with changes in sensory experiments for binary mixtures. The results provide insights into the molecular mechanisms of odorant-polymer interactions in red wine with the potential of DFT calculations as a tool for predicting and tailoring red wine aroma.

NMR-Based Studies on Odorant Polymer Interactions and the Influence on the Aroma Perception of Red Wine.

The aroma of red wine is suggested to be influenced by interactions with nonvolatile polymers. To investigate this aroma binding effect in red wine, the key aroma compounds of a Primitivo red wine were quantified using GC-MS and an aroma recombinant with 27 odorants was prepared. In sensory experiments, an overall strong effect on the odor perception of the aroma recombinant was observed when high-molecular-weight (HMW) polymers of Primitivo red wine were added. An 1H NMR-based approach was developed to get an insight into the molecular mechanisms of this aroma binding effect in red wine. Evaluation of qualitative changes in the NMR spectra and quantitative time-dependent measurements revealed a clear distinction between different molecular interaction types: (i) no interactions for esters, alcohols, furanones, ketones, and C13-norisoprenoids, (ii, iii) noncovalent interactions for acids, aldehydes, and lactones, and (iv) π-π interactions for pyrazines and phenols. Additionally, the influence of the molecular weight of polymers was evaluated, where the HMW fraction 30-50 kDa showed the highest interaction activity, for example for π-π interactions. Based on these results, the new approach allowed the direct analysis of noncovalent interactions between odorants and HMW polymers and therefore allowed for the first time the description of the aroma binding effect on a molecular basis.

NMR-Based Tastant Polymer Interaction Studies and the Influence on the Taste Perception of Red Wine.

Using a quantitative 1H NMR-based approach, molecular interactions between key taste active compounds and high-molecular-weight (HMW) polymers were directly investigated in red wine. Analysis of qualitative and quantitative 1H NMR spectra over time allowed a distinction of three interaction scenarios: (i) no interactions for flavon-3-ol glycosides, ellagitannins, carbohydrates, and amino acids; (ii) changes in the chemical shift to lower frequencies for flavan-3-ols and phenolic acid ethyl esters; and (iii) changes in the chemical shift to higher frequencies for phenolic acids, organic acids, inorganic salts, and alditols. Additionally, using liquid chromatography-tandem mass spectrometry (LC-MS/MS), quantitative 1H nuclear magnetic resonance (qHNMR), and high-performance ion chromatography (HPIC), a taste reconstitution model of Primitivo red wine was established for the first time. Human sensory experiments with the new taste recombinant and different HMW fractions demonstrated the influence of the tastant polymer interactions on the sour and salty taste perception of red wine and the intrinsic bitter and astringent taste of the polymers. Further, the influence of the molecular weight cutoff (MWCO) of the polymers and the pH value on the tastant polymer interactions was analyzed. Especially, the HMW fractions 30-50 kDa and >50 kDa caused strong shifts to lower and higher frequencies, respectively. NMR-based interaction studies at different pH values revealed a maximum of interactions at pH 4.0. Based on these results, flavor changes in red wine caused by tastant polymer interactions can be predicted on a molecular level in the future.

Key odorant melanoidin interactions in aroma staling of coffee beverages.

Fractionation of high molecular weight (HMW) coffee melanoidins of varying roasting intensity and evaluation of aroma binding activity via nuclear magnetic resonance spectroscopy revealed two fractions 5-10 kDa and > 50 kDa with high and selective binding affinity toward key coffee odorants. Quantification of monosaccharides, amino acids and phenolic acids, as well as aliphatic organic acids in hydrolysates of HMW material indicated the importance of aromatic residues in the form of hydroxycinnamic acids for the formation of non-covalent interactions with odorants. Caffeic acid concentrations were up to four times higher in fractions 5-10 kDa and > 50 kDa compared to 30-50 kDa and 10-30 kDa fractions. A minimization strategy was developed involving alkaline treatment of the most affine HMW fractions followed by reconstitution at typical coffee concentrations. These reconstituted HMW fractions exhibited up to 25% less aroma binding compared to native fractions of coffee.

Identification and Quantitation of Reaction Products from Quinic Acid, Quinic Acid Lactone, and Chlorogenic Acid with Strecker Aldehydes in Roasted Coffee.

To gain comprehensive insight into the interactions of key coffee odorants, like the Strecker aldehydes, acetaldehyde, propanal, methylpropanal, 2- and 3-methylbutanal, and methional, and the nonvolatile fraction of coffee, an untargeted metabolomics approach was applied. Ultra performance liquid chromatography (UPLC)-time of flight (TOF)-mass spectrometry (ESI-) profiling followed by statistical data analysis revealed a marker substance for a coffee beverage spiked with acetaldehyde with an accurate mass of 217.0703 [M - H]-. This compound could be identified as a reaction product of quinic acid (QA) and acetaldehyde linked by acetalization at the cis-diol function of QA. Consequently, the acetalization of aldehydes, QA, 5-O-caffeoyl quinic acid (CQA), and quinic acid γ-lactone (QAL) was investigated by means of model reactions, followed by synthesis, isolation, and structure elucidation via UPLC-TOF-MS and 1D and 2D NMR techniques. UHPLC-MS/MSMRM screening and the quantification of aldehyde adducts in coffee beverages revealed the presence of QA/acetaldehyde, -/propanal, -/methylpropanal, and -/methional reaction products and CQA/acetaldehyde, -/propanal, -/methylpropanal, -/2- and 3-methylbutanal, and -/methional and QAL/acetaldehyde adducts for the first time, in concentrations of 12-270 µg/L for QA/aldehydes, 5-225 µg/L for CQA/aldehydes, and 62-173 µg/L for QAL/acetaldehyde. The sensory characterization of the identified compounds showed bitter taste recognition thresholds of 48-297 µmol/L for CQA adducts and 658 µmol/L for QAL/acetaldehyde, while the QA adducts showed no bitter taste (<2000 µmol/L).