Volatile components of cocoa with particular reference to glucosinolate products

Abstract

The aroma volatiles of raw, fermented and roasted cocoa beans were extracted and concentrated to valid essences using well-established techniques. Analysis by GC and GC/MS showed at least 84 components of which 13 were identified for the first time as cocoa volatiles. In total, ca 5,66 and 65 μg of aroma components were obtained per g of raw, fermented and roasted cocoa beans, respectively. The most abundant groups of volatiles from fermented beans were alcohols ( ca40%w/w of the total volatiles) and esters ( ca 32%), whilst those from roasted beans were pyrazines ( ca 40%) and aldehydes ( ca 23%). Trimethyl- and tetramethylpyrazine were also detected in fermented beans, and it is suggested that they contribute to the noticeable cocoa/chocolate aroma of fermented unroasted beans. Phenylacetonitrile, benzyl isothiocyanate and benzyl thiocyanate were all identified amongst cocoa volatiles, together showing the presence of precursor benzylglucosinolate in cocoa. Glucosinolate products were detected in roasted beans, and it seems likely that the enzyme thioglucoside glucohydrolase survived the conditions of roasting. Benzyl thiocyanate was detected only in raw beans, showing that the glucosinolate ‘thiocyanate–forming factor’ did not withstand conditions of fermentation