Abstract
We aimed to investigate the effect of roasting time on the chemical structure of coffee melanoidins and how the incorporation of chlorogenic acids (CGA) occurs using one-dimensional and two-dimensional Nuclear Magnetic Resonance spectroscopy (1D and 2D NMR). 1H NMR spectra showed large signals suggestive of proteins and polysaccharides due to their reduced intrinsic mobility. The spectra also revealed that melanoidins molecular weight increased during intermediate times of roasting and slightly decrease thereafter. In roasted samples, HSQC 2D NMR spectra showed 1H,13C cross-peaks from aromatic and olefinic groups of CGA. COSY 2D NMR experiments without and with enrichment of 5-caffeoylquinic acid standard allowed the detection of all 1H,1H cross-peaks from CGA, suggesting their intact incorporation, which was confirmed by a 1H NMR experiment using a T2-filter to remove large signals from macromolecules. Together, our results show that CGA are linked to coffee melanoidins by strong chemical bonds.
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