Thermal processing of pomegranate seed oils underscores their antioxidant stability and nutritional value: Comparison of pomegranate seed oil with sesame seed oil

In the present study, the oxidative stability and antioxidant activity of seed oils were investigated in three Iranian pomegranate cultivars, Shirin Khafr, Torsh Sabz, and Rabab, along with the sesame (Sesamum indicume L. cv Dezful) seed oil. Punicic acid was the primary fatty acid in the pomegranate seed oils, with contents ranging from 75.5 to 80.9% (w/w). The tocopherol levels in pomegranate seed oils ranged from 1439 to 2053 mg/kg, whereas the phenolics ranged from 130 to 199.3 mg/kg, respectively. Comparatively, in the seed oil of sesame “Dezful,” these substances' contents were 1053 and 79 mg/kg, respectively. Contrary to common perception, the seed oil of the three pomegranate cultivars cultivated in Iran had high oxidative stability and antioxidative activity during the 32 h of thermal processing at 170°C. The oxidation stability assayed by peroxide value, p-anisidine value, and TOTOX index revealed that the pomegranate seed oils had a much higher resistance to the oxidation process than the sesame oil. The content of tocopherols increased during thermal processing due to the regeneration phenomenon. Tocopherols are not always free and may form a matrix with themselves or other compounds. Changes in the antioxidant activity during the thermal processing assessed by DPPH free radical scavenging power and by the FRAP test were consistent with those for the antioxidants. Therefore, these oils can be added to other edible oils as a natural antioxidant to improve their oxidative stability.