Flavoromics approach in monitoring changes in volatile compounds of virgin rapeseed oil caused by seed roasting

• Virgin oil from roasted and unroasted seeds of two varieties of rapeseed was compared.
• GC × GC-ToFMS and GC-O were used to monitor volatiles and odorants in roasting process.
• Canolol content increased dramatically during roasting.
• High oleic acid and high linolenic acid varieties behaved similarly during roasting.

Two varieties of rapeseed (one high oleic – containing 76% of oleic acid, and the other – containing 62% of oleic acid) were used to produce virgin (pressed) oil. The rapeseeds were roasted at different temperature/time combinations (at 140–180 °C, and for 5–15 min); subsequently, oil was pressed from the roasted seeds. The roasting improved the flavour and contributed to a substantial increase in the amount of a potent antioxidant–canolol. The changes in volatile compounds related to roasting conditions were monitored using comprehensive gas chromatography–mass spectrometry (GC × GC-ToFMS), and the key odorants for the non-roasted and roasted seeds oils were determined by gas chromatography–olfactometry (GC-O). The most important compounds determining the flavour of oils obtained from the roasted seeds were dimethyl sulphide, dimethyltrisulfide, 2,3-diethyl-5-methylpyrazine, 2,3-butenedione, octanal, 3-isopropyl-2-methoxypyrazine and phenylacetaldehyde. For the oils obtained from the non-roasted seeds, the dominant compounds were dimethylsulfide, hexanal and octanal. Based on GC × GC-ToFMS and principal component analysis (PCA) of the data, several compounds were identified that were associated with roasting at the highest temperatures regardless of the rapeseed variety: these were, among others, methyl ketones (2-hexanone, 2-heptanone and 2-octanone).