Application of Untargeted Flavoromic Analysis to CharacterizeChemical Drivers of Coffee Quality

Increasing global demand for premium coffee beverages has challenged coffee producers to provide higher quality products. The overall aim of this project was to characterize the chemical composition of coffee brews that contribute to different flavor quality and ultimately to provide a chemical basis for the optimization of coffee production. During the initial phase of this study, current industrial methods for green bean selection were evaluated in regard to their ability to predict coffee brew sensory properties. Physico-chemical changes observed in the green coffee beans stored under different conditions were not indicative of coffee brew flavor changes in this study. Overall, these results supported the need to develop new methods for coffee quality prediction. In the second phase of this project, an untargeted Liquid Chromatography/Mass Spectrometry (LC/MS) Flavoromics approach was used to define chemical markers predictive of coffee brew quality. Eighteen coffees ranging in qualities from below specialty to excellent specialty quality, were chemically profiled and modeled against the official Specialty Coffee Association cup score (obtained by Q-graders) using Orthogonal Partial Least Square (OPLS). A successful model was generated and showed high prediction ability (R2Y=0.99, Q2=0.97). A total of 10 highly predictive compounds were selected, of which six were positively and four were negatively correlated to cup score. Their sensory impact was evaluated using a recombination study performed by five Q-graders. Addition of the compounds individually and in combination to a coffee brew base caused significant changes in cup scores. Three compounds predictive of high cup score: 3-O-caffeoyl-1-O-3-methylbutanoylquinic acid (m/z 437), 3-O-caffeoyl-1-O-3-methylbutanoyl-1, 5-quinide (m/z 419) and a chlorogenic acid derivative (m/z 671) significantly increased the quality of a below specialty grade coffee brew to excellent specialty grade. Four compounds predictive of low cup score; ent-16α,17-kauran-19-diglucoside (m/z 659), its aglycone form ent-16α,17-dihydroxy-kauran-19-oic acid (m/z 335), unknown compounds m/z 351 and m/z 9.48_333 significantly decreased the coffee quality score of a high cup score coffee. All the identified compounds had no or slight flavor activity when evaluated in water at the levels present in coffee. Yet they were able to significantly modulate the flavor of coffee, likely through the existence of perceptive interactions. The presence of these seven markers of coffee brew quality in the green bean was further investigated. Markers 3-O-caffeoyl-1-O-3-methylbutanoylquinic acid and ent-16α,17-dihydroxy-kauran-19-diglucoside were both detected in green coffee beans at levels correlated to the coffee brew cup scores. Overall, this research showed a successful application of a newer flavor analysis method, Flavoromics, that allowed for the discovery of seven flavor compounds predictive of the coffee cup quality. These compounds can be used as markers of quality for raw material selection and process optimization to achieve desirable coffee brew flavor.