Molecular Background of a Moldy-Musty Off-Flavor in Cocoa.

The parallel application of aroma extract dilution analysis to the volatiles isolated from a sample of fermented cocoa seeds with a pronounced moldy-musty off-flavor and to the volatiles isolated from a flawless reference sample revealed (-)-geosmin, 4-methoxy-2,5-dimethylfuran-3(2H)-one, 1H-indole, and 3-methyl-1H-indole as potential off-flavor compounds on the basis of their odor quality and higher flavor dilution factors in off-flavor cocoa than in the reference sample. Quantitation of the four compounds in nine off-flavor cocoa samples and calculation of odor activity values (ratio of the concentrations to the odor threshold values) suggested the crucial roles of (-)-geosmin and 3-methyl-1H-indole for the off-flavor. In the chocolate industry, their quantitation can be used to objectively assess the off-flavor at the level of incoming goods inspection. Because both compounds are inhomogeneously distributed between the testa and the embryo, separate quantitation in the two parts of the seeds is required.

Enantioselective synthesis of tri-deuterated (-)-geosmin to be used as internal standard in quantitation assays.

For the accurate and sensitive quantitation of the off-flavor compound geosmin, particularly in complex matrices, a stable isotopologue as internal standard is highly advantageous. In this work, we present a versatile synthetic strategy leading from (4aR)-1,4a-dimethyl-4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one to tri-deuterated (-)-geosmin ((4S,4aS,8aR)-4,8a-dimethyl(3,3,4-2 H3 )octahydronaphthalen-4a(2H)-ol). The starting material was readily accessible from inexpensive 2-methylcyclohexan-1-one using previously published procedures.