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RESEARCH PRODUCT

Characterization of water mobility in dry and wetted roasted coffee using low-field proton nuclear magnetic resonance

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Abstract Roasted and ground coffee was studied by low-field 1 H nuclear magnetic resonance at various water contents and temperatures. The spin–spin relaxation times ( T 2 ) were measured with single pulse free induction decay (FID) and Carr–Purcell–Meiboom–Gill (CPMG) sequences. Four relaxing components were distinguished: the solid population was observed with FID sequence at T 2s ∼9 μs; the other three populations, measured with the CPMG sequence, corresponded to an apolar phase, the coffee oil, and two polar phases. The two polar populations, observed at T 2m ∼6 ms and ∼27 ms (for coffee with 50% water content at 90 °C) were attributed to water in cell wall polymers and in water filling cells lumen. The T 2 values appeared relatively insensitive to temperature, showing an Arrhenius type evolution with no break due to an important structure change. Furthermore, the intensity of the mobile phase increased as a function of time up to ∼10 min after wetting, providing information about water absorption dynamics in roasted coffee.