Key aroma compounds in fermented Forastero cocoa beans and changes induced by roasting

The influence of the roasting procedure on the composition of key aroma compounds in fermented Forastero cocoa beans was investigated. For this purpose, the volatile fractions from the unroasted, fermented and the roasted cocoa were isolated by extraction/SAFE distillation, and the odour-active constituents were characterised by gas chromatography-olfactometry in combination with an aroma extract dilution analysis. A total of 41 aroma compounds in the flavour dilution (FD) factor range of 2-8192 were identified in the unroasted and 42 compounds with FD factors of 2-8192 in the roasted cocoa beans. Qualitatively, the set of aroma compounds was nearly identical in both samples; however, differences in the flavour dilution factors were observed. 2- and 3-Methyl butanoic acid (sweaty) and acetic acid (vinegar-like, sour) showed the highest FD factors in the unroasted beans, while 3-methylbutanal (malty), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like) and 2- and 3-methyl butanoic acid (sweaty) were detectable by GC/O in the highest dilutions in the roasted seeds. Quantitation of the most odour-active compounds by means of stable isotope dilution assays, followed by calculation of odour activity values (OAV, ratio of concentration to odour threshold), revealed concentrations above the threshold level for 20 compounds in the unroasted and 24 compounds in the roasted beans. The roasting procedure led to a strong increase, in particular, in the concentrations of the two Strecker aldehydes 3-methylbutanal (malty) and phenylacetaldehyde (honey-like) as well as 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like).