Changes in volatiles of palm kernel oil before and after kernel roasting

• Effect of roasting on volatiles of palm kernel oil (PKO) was studied.
• Volatiles changed dramatically in type and amount after roasting.
• Pyrazines, furans, pyrans and cyclic ketones were key volatiles in roasted PKO.
• Maillard and caramelisation reactions enhanced PKO aroma.

Palm kernel oil (PKO) is obtained from the seeds of oil palm (Elaeis guineensis Jackqu). In this study, volatiles and aroma-active compounds of PKO were studied by head-space solid-phase microextraction/gas chromatography/mass spectrometry/flame ionisation detector (HS-SPME/GC/MS/FID) and solvent-assisted flavour evaporation -gas chromatography/olfactometry/mass spectrometry (SAFE-GC/O/MS), respectively. An optimised HS-SPME sampling method was obtained for extraction at 60 °C for 40 min. With this method, the volatiles of PKO from palm kernels subjected to different roasting times (up to 30 min) at 180 °C were analysed. Totally 73 volatiles were found, including 19 O-heterocyclic compounds (16 furans and 3 pyrans), 15 N-heterocyclic compounds (10 pyrazines and 5 others), 15 carbonyl compounds (5 aldehydes and 10 ketones), 11 acids, 4 alcohols, 3 esters, 3 sulphur and 3 volatile phenols. With the extension of roasting times, peak areas of O-heterocyclic compounds, N-heterocyclic compounds, aldehydes and cyclic ketones increased significantly whereas those of acids, alcohols and esters generally decreased. Results of GC/O/MS showed that 2-nonanone, octanoic acid and methyl octanoate were the most aroma-active compounds in unroasted PKO, while in roasted PKO, the most active volatiles were ethyl pyrazine, 2-nonanone, 2-hydroxy-3-methyl-2-cyclopenten-1-one, maltol, 2,6-dimethylpyrazine, 2,5-dimethylpyrazine, 2,3-dimethylpyrazine, benzoic acid ethyl ester, octanoic acid, 5-methyl-2-furancarboxaldehyde and isomaltol.