Abstract
Coffee brings many health benefits due to its chemical constituents. Based on this information, it is essential to know the main chemical compounds from coffee granules; the intermolecular interaction among the coffees compounds and the molecular components homogeneity. In this study six types of roasted commercial coffee were evaluated by solid state nuclear magnetic resonance (NMR), employing carbon-13 (13C) and hydrogen (1H) nucleus. Carbon-13 was analyzed applying high field NMR techniques, such as: magic angle spinning (MAS); magic angle spinning with cross-polariza- tion (CPMAS) and magic angle spinning with cross-polarization and dipolar dephasing (CPMASDD). The hydrogen was evaluated via relaxation times. Proton spin-lattice relaxation time in the rotating frame was deter-mined through the carbon-13 decay, during the variable contact-time experiment, using high field NMR. Proton spin-lattice relaxation time was determined through the inversion-recovery pulse sequence, using low field NMR. Considering all NMR results, it was concluded that the major coffee compounds are: a) triacilglycerides, which constitute the mobile region in the granule coffee and b) Carbohydrates such as: polysaccharides and fibers that belong to the rigid domain. These constituents belong to different molecular mobility domain, although they have strong intermolecular interactions due to the granule organization.
Highlights
Coffee is very much consumed in Brazil and all over theworld, for this reason it is very well studied [1,2,3,4,5]
Considering all NMR results, it was concluded that the major coffee compounds are: 1) triacilglycerides, which constitute the mobile region in the granule coffee and 2) Carbohydrates such as: polysaccharides and fibers that belong to the rigid domain
From the 13C NMR magic angle spinning (MAS) spectra (Figure 1) it was identified signals which refer to carbons which belong to the mobile region present in the coffee samples (Table 1), due to the use of short recycle delay between 90 degree pulses
Summary
Coffee is very much consumed in Brazil and all over theworld, for this reason it is very well studied [1,2,3,4,5]. Many techniques can be used to evaluate toasted coffees; among them solid state nuclear magnetic resonance (NMR) is one of the best techniques for that, because it permits analyzing coffee granules in their total form, and it informs on chemical structure; components interaction and molecular homogeneity at molecular level [15,16,17,18,19]. From variable contact time the values of proton spinlattice relaxation time in the rotating frame can be determined from the decay of all resolved carbons, which permits evaluating the molecular dynamic [21] in the scale of tens of kHz. The 13C CPMASDD experiment was carried out observing the molecular rigid components present in the coffees granules due to the detection of non protonated carbon [21]. Hydrogen nuclei will be evaluated through the proton relaxation time [22], which will be measured directly in a low filed NMR spectrometer, employing inversion-recovery pulse sequence [23]
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