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.