Extraction and Analysis of Volatile Compounds

Volatile compounds from kernel and oil were extracted by solid-phase microextraction (SPME) [13 (link)]. Briefly, 3.0 g of grounded kernel flour or extracted oil was mixed with 2.5 mg/kg of 4-methyl-2-pentanol (internal standard), stirred for 10 min at 40 °C until equilibration in a 20 mL glass vial with a PTFE/silicone septum (Agilent Technologies, Palo alto, CA, USA). Next, a solid phase microextraction (SPME) fiber (DVB/CAR/PDMS, Sigma-Aldrich, St. Louis, MO, USA) was exposed to the sample headspace for 40 min. Next, the volatile compounds were analyzed with a GC system (Agilent Technologies) comprising an autosampler (Agilent PAL RSI 85), gas chromatograph (GC Agilent 7820A) and mass spectrometer (Agilent 5977B) designed with an electron impact source and quadrupole analyzer. Volatile compounds were separated with a Supelcowax 10 column (30 m × 0.25 mm × 0.25 µm, Sigma-Aldrich, USA) using helium as a carrier gas at a flow rate of 1 mL/min. GC oven temperature was started at 40 °C and increased by 3 °C/min after 10 min, until it reached a final temperature of 200 °C. Volatiles were identified by two methods, including the use of NIST 08 Mass Spectral Library and comparison of their retention time and mass spectrum to their respective standards. Results were expressed as µg of internal standard per kg of kernel or oil sample.