Identification and origin of the character-impact compounds of raw oyster Crassostrea gigas

The French consume large amounts of raw oysters. The study of the aroma of oyster Crassostrea gigas is of economic interest because it is a good method of checking the sensory quality. Aromas were extracted by vacuum steam distillation at 20degreesC using whole oyster flesh. This extract presented similar sensory characteristics to raw oyster. The odour-active compounds were characterised by gas chromatography coupled with olfactometry using a panel of 10 judges trained in seafood aroma recognition. Fifty-nine volatile compounds were identified in oyster aroma extract. Among these, 25 were responsible for the overall odour of raw oyster. Four compounds identified in oysters were characterised by fresh and marine odour: 3-(E)-hexen-1-ol, decanal, 2-undecanone and 3,6-(E,Z)-nonadien-1-ol. Some compounds were identified for the first time in oysters: 4-(Z)-heptenal (white boiled fish odour), which comes from n-3 polyunsaturated fatty acid oxidation, and 3-octanol (moss and sulphury odour), 2-nonanol (cucumber odour) and octanoic acid, which arise from n-6 polyunsaturated fatty acid oxidation. (C) 2002 Society of Chemical Industry.