Air frying as a heat pre-treatment method for improving the extraction and yield of canolol from canola seeds

Roasting of canola seeds prior to oil extraction is essential for producing unique flavors and heat-induced formation of novel phenolic compounds. This study investigated the efficacy of air frying as a seed roasting pre-treatment technique to improve the recovery of canolol and other oil-soluble sinapic acidic derivatives (SADs) from canola seeds. Air frying of canola seeds was carried out at temperature-time regimens of 160, 170, 180 or 190 ◦ C for 5, 10, 15, or 20 min, respectively. Oil was extracted by the Soxtec method and the soluble SADs were extracted from the oil by addition of an equal volume of hexane/70% methanol mixture followed by quantification using high performance liquid chromatography-diode array detection (HPLC-DAD). The total phenolic content (TPC) and antioxidative activity of the oils were also evaluated. The results indicated a time-temperature association for the recovery of canolol. The optimum air frying condition at 190 o C for 15 min produced the maximum yield of canolol (1439 ± 45.6 μg/100 g roasted seed) in addition to other unidentified SADs. The oil extracts obtained from canola seed roasted at 180, 15 min, 190 o C, 15 and 20 min showed the highest TPC (0.387 ± 0.015, 0.413 ± 0.002 and 0.419 ± 0.002 mg GAE/g oil), respectively, and the strongest antioxidant activities (DPPH radical scavenging and iron reducing), but exhibited weak metal ion chelating activity. There was a strong positive correlation of canolol content to the antioxidant activities (DPPH, FRAP) and TPC value for the canola oil extracts (r=0.85, r=0.93 and 0.88), respectively.