NMR-Based Studies on Odorant-Melanoidin Interactions in Coffee Beverages

A quantitative H-1 NMR-based approach was established, which allowed the direct and noninvasive analysis of molecular interactions between key coffee odorants and high-molecular-weight (HMW) melanoidin polymers. A clear distinction between covalent and noncovalent interactions was achieved by monitoring the time dependency of odorant-polymer interactions, resulting in four scenarios: covalent, pi-pi, covalent and pi-pi-, as well as no interactions. Evaluation of temperature influence on e.g. 2-furfurylthiol (FFT), revealed an altered behavior with increased pi-pi stacking at lower temperatures and accelerated covalent interactions at higher temperatures. Human sensory experiments with HMW material and a coffee aroma reconstitution model showed a drastic reduction of roasty/sulfury aroma notes, as well as an increased sweetish/caramel-like flavor. The lack of interactions between the sweetish/caramel smelling 4-hydroxy-2,5-dimethyl-3(2H)-furanone with the HMW melanoidins in combination with the high binding affinity of coffee thiols explains the sensory evaluation and is obviously the reason for the fast disappearance of the typical roasty/sulfury aroma impressions of a freshly prepared coffee brew.

Automated summary

A quantitative H-1 NMR-based approach was established for direct and noninvasive analysis of molecular interactions between key coffee odorants and high-molecular-weight melanoidin polymers, distinguishing between different types of interactions and evaluating the temperature influence on these interactions. Human sensory experiments showed a reduction in roasty/sulfury aroma notes and an increase in sweetish/caramel-like flavor in HMW material and a coffee aroma reconstitution model.