Key odorant melanoidin interactions in aroma staling of coffee beverages.

ABSTRACT

Fractionation of high molecular weight (HMW) coffee melanoidins of varying roasting intensity and evaluation of aroma binding activity via nuclear magnetic resonance spectroscopy revealed two fractions 5-10 kDa and > 50 kDa with high and selective binding affinity toward key coffee odorants. Quantification of monosaccharides, amino acids and phenolic acids, as well as aliphatic organic acids in hydrolysates of HMW material indicated the importance of aromatic residues in the form of hydroxycinnamic acids for the formation of non-covalent interactions with odorants. Caffeic acid concentrations were up to four times higher in fractions 5-10 kDa and > 50 kDa compared to 30-50 kDa and 10-30 kDa fractions. A minimization strategy was developed involving alkaline treatment of the most affine HMW fractions followed by reconstitution at typical coffee concentrations. These reconstituted HMW fractions exhibited up to 25% less aroma binding compared to native fractions of coffee.