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

Area of Science:

• Food Chemistry
• Analytical Chemistry
• Sensory Science

Background:

• Coffee aroma is complex, influenced by interactions between volatile compounds and non-volatile polymers like melanoidins.
• Understanding these interactions is crucial for preserving coffee's desirable sensory attributes.

Purpose of the Study:

• To investigate the molecular interactions between key coffee odorants and high-molecular-weight (HMW) melanoidins.
• To elucidate the mechanisms (covalent vs. noncovalent) governing these interactions.
• To correlate molecular interactions with observed changes in coffee aroma and flavor.

Main Methods:

• Quantitative 1H Nuclear Magnetic Resonance (NMR) spectroscopy for direct, noninvasive analysis of molecular interactions.
• Monitoring time-dependent odorant-polymer interactions to distinguish between covalent and noncovalent binding.
• Evaluating the influence of temperature on interaction dynamics.
• Human sensory experiments using a coffee aroma reconstitution model.

Main Results:

• NMR successfully differentiated between covalent, noncovalent (π-π stacking), and combined interaction scenarios.
• Temperature significantly affected interactions: lower temperatures favored π-π stacking, while higher temperatures accelerated covalent binding.
• Sensory analysis revealed a reduction in "roasty/sulfury" notes and an increase in "sweetish/caramel-like" flavors.

Conclusions:

• The binding affinity of coffee thiols to HMW melanoidins, coupled with the lack of interaction with "sweetish/caramel" compounds, explains the rapid loss of typical coffee aroma.
• This study provides a molecular basis for understanding aroma loss in brewed coffee.
• The established NMR approach offers a powerful tool for analyzing complex food matrix interactions.