Air frying-ultrasound-aided extraction: a combination approach for improving the extraction of polyphenols and antioxidant potential of canola co-product

Abstract: The current study examined the efficacy of roasting by air frying combined with ultrasound-aided extraction (UAE) to enhance the extraction and recovery of the predominant sinapic acid derivatives (SADs) from canola meal and the antioxidant potential of the extracts. Canola meal was obtained by air frying canola seed at 160, 170, 180, and 190 °C for 5, 10, 15, and 20 min, respectively. Oil removal was done by the Soxtec method. Defatted canola meal was extracted for phenolic compounds by ultrasound-assisted extraction with 70% (v/v) methanol. The major SADs were quantified by high-performance liquid chromatography-diode array detection (HPLC-DAD). The antioxidant potential of the meal extracts was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power assay (FRAP), and metal ion-chelating activity (MIC) as well as the total phenolic content (TPC). Sinapine, sinapic acid and RT- 26.6 min compound were the major sinapates identified with highest concentration (7572 ± 479 µg/g DW, 727 ± 44 µg/g DW and 1763 ± 74 µg/g DW) at 160 °C for 5 min for sinapine, sinapic acid and RT-26.6 min compound, respectively. Also, an appreciable amount of canolol (151 ± 7.7 µg/g DW) was obtained at an air frying temperature of 170 °C for 20 min. The highest TPC (3.15 mg GAE/g DW) was observed in meal extract obtained at 190 °C, 15 min air frying condition. The FRAP and MIC correlated positively (r=0.85) and generally decreased with increased air frying temperature- time condition with the highest FRAP and MIC values (0.53 mM and 79.9%) obtained at 160, 5 min, and 20 min, respectively. These findings will contribute new knowledge to the value-added processing and by-product utilization of canola seed.