Effect of ultrasonic and microwave assisted extraction on the oxidative stability, phytochemical and antioxidative properties of Himalayan walnut oil

Himalayan walnuts form an important sink of walnut oil. In order to utilize the cull grade walnuts for walnut oil production, the present research was devised to extract oil by maceration extraction (ME), ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE) to obtain oils with better process yield and intact techno-functional properties. Among the extraction methods, UAE showed the highest (p <= 0.05) oil yield (63.68%) followed by MAE (58.83%) and ME (39.83%). The lowest peroxide value (PV) was observed in ME (1.11 meq O2 kg-1 oil) while as, MAE showed the highest PV (2.0 meq O2 kg-1 oil). The highest polyunsaturated fatty acid (PUFA) content (p <= 0.05) was observed in MAE (83.01%). However, the highest monounsaturated fatty acid (MUFA) content (p <= 0.05) was observed in UAE (13.74%). ME showed the highest amount (p <= 0.05) of tocopherols and bioactive phytosterols. Methanolic extracts of MAE depicted highest activity against DPPH (1,1-(diphenyl-2-picrylhydrazyl*) radical scavenging capacity (345 mg AA/kg oil), ABTS 2,2 '-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid*) (57.93%) and metal chelation (55.38%) Correlation analysis depicted a negative correlation between peroxide value with TPC and TTC (r = - 6759 r = - 6502, - 0.509), however a strong positive correlation was seen between antioxidant properties and minor components (r = 0.8481-0.998). In conclusion, amongst all extraction methods, UAE could be employed for the production of high-quality oil with promising phytochemical profile and nutraceutical potential.