Characterization of the Key Odorants in Commercial Cold-Pressed Oils from Unpeeled and Peeled Rapeseeds by the...

By application of aroma extract dilution analysis (AEDA) on the volatile fraction isolated from commercial cold-pressed rapeseed oil prepared from unpeeled seeds, 35 odor-active constituents in the flavor dilution (FD) factor range of 8-8192 were detected. The identification experiments showed that the earthy, pea-like-smelling 2-isopropyl-3-methoxypyrazine showed the highest FD factor of 8192, followed by 1-octene-3-one (FD 4096) and (E,Z)-2,6-nonadienal with an FD of 2048. After quantitation of the 16 key odorants showing FD factors ≥32 by stable isotope dilution assays and a determination of their odor thresholds in deodorized sunflower oil, odor activity values (OAV; ratio of concentration to odor threshold) could be calculated. The results indicated 2-isopropyl-3-methoxypyrazine, (E,E)-2,4-nonadienal (deep-fried, fatty), and (E,Z)-2,6-nonadienal (cucumber-like) with the highest OAVs. To confirm that the key aroma compounds were correctly identified and quantitated, a recombination experiment was performed by mixing the reference odorants in the same concentrations as they occurred in the rapeseed oil using odorless sunflower oil as the matrix. The recombinate showed a very good agreement with the overall aroma of the oil. In a commercial rapeseed oil prepared from peeled seeds, the same odorants were identified; however, in particular, the FD factor of dimethyl sulfide (DMS) was clearly higher. Quantitation of DMS in 10 commercial rapeseed oils from either peeled and unpeeled seeds revealed significant differences in DMS, but no influence of the peeling process on the amounts of DMS was found. The data can serve as a basis for the quality assessment of cold-pressed rapeseed oil.