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(2)-one, 1-indole, and 3-methyl-1-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-1-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.

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- H )octahydronaphthalen-4a(2H)-ol). The starting material was readily accessible from inexpensive 2-methylcyclohexan-1-one using previously published procedures.