The Measurement of Monocarbonyl Classes in Cocoa Beans and Chocolate Liquor With Special Reference to Flavor

SUMMARY Monocarbonyl compounds in unroasted cocoa beans and chocolate liquor were converted to 2,4‐dinitrophenylhydrazones and then separated into methyl ketone, saturated aldehyde, 2.enal, and 2,4‐dienal fractions. In most comparisons the aldehydes were more concentrated in liquor than in unroasted beans, which contained more ketone. Over 30 derivatives, several within each class, were detected on thin‐layer plates. Spot densities were most intense in the region between the C 4 and C 7 standards. Differences among Accra, Arriba, and Bahia varieties involved relative concentrations of individual compounds rather than the presence or absence of specific carbonyls. Regeneration of carbonyls revealed each class to be a potent reservoir of aroma‐emitting compounds. Methyl ketones were cheese‐like; saturated aldehydes, waxy and fruity; 2.enals, oxidized, painty, and like old meat; 2,4‐dienals, nutmeg and spicy. From the quantitative data it was concluded that each carbonyl class is an important contributor to chocolate aroma.