Identification of Compounds that Negatively Impact Coffee Flavor Quality Using Untargeted Liquid Chromatography/Mass Spectrometry Analysis.

Untargeted liquid chromatography/mass spectrometry (LC/MS) flavoromics analysis was carried out on 18 coffee brews ranging in Specialty Coffee Association (SCA) cup scores. Six compounds highly predictive of low cup score were isolated from coffee using multidimensional preparative LC/MS and further evaluated by sensory recombination analysis with certified SCA quality graders. A significant decrease in cup score was demonstrated with four of the six compounds when added to a specialty coffee brew. High-resolution mass spectrometry and mono- and bidimensional nuclear magnetic resonance experiments were used to successfully elucidate four of the structures as 16α,17-dihydroxy-ent-kauran-19-oic acid (compound 1), its diglycosidic compound 16α,17-dihydroxy-ent-kauran-19-diglycoside (compound 2), 16α,17,18-trihydroxy-ent-kauran-19-oic acid (compound 5), and 16α-hydroxy-17-ent-kauren-19-oic acid (compound 6). All four ent-kaurane diterpene compounds were endogenous to green coffee beans, providing direct chemical indicators of low-quality coffee.

Identification of flavor modulating compounds that positively impact coffee quality.

Untargeted LC/MS flavoromic profiling was utilized to identify compounds that positively impact coffee quality. The chemical profiles of eighteen coffee samples and the corresponding Specialty Coffee Association (SCA) cup scores were modeled by orthogonal partial least squares (OPLS) analysis with good fit and predictive ability (R2Y > 0.9, Q2 > 0.9). Four highly predictive chemical compounds positively correlated to cup score were subsequently isolated and purified (>90%) by multi-dimensional preparative LC/MS fractionation. Sensory recombination analysis by certified SCA Q-graders (n = 5) confirmed three out of four compounds significantly increased cup score when added to a control coffee (p < 0.001). Based on accurate mass spectrometry and NMR experiments, the compound structures were identified as novel compounds 3-O-caffeoyl-4-O-3-methylbutanoylquinic acid, and the corresponding lactone 3-O-caffeoyl-4-O-3-methylbutanoyl-1,5-quinide, as well as an unknown phenolic derivative containing a 3-methylbutanoyl moiety ([M-H]-1, m/z 671). No direct flavor activity was observed for each compound, indicating these compounds act as flavor-modifiers.