Chemical properties of solvent extracted and cold-pressed oil from pretreated pomegranate seed: a comparison study

Considering the rapid growth of the pomegranate fruit juice industry, if unmanaged, waste generated from processing the fruit, including seeds and peels, may cause environmental problems. Besides, these by-products have been reported to possess more bioactive phytochemicals with health benefits than juice, the edible part of the fruit. Therefore, the value addition of pomegranate seed into oil provides a more valuable way of utilising the postharvest waste. Both oil extraction and seed pretreatment are critical factors in determining the quality of pomegranate seed oil. This work presents a comparative study on the chemical properties of ultrasound-assisted solvent (hexane) extracted and cold-pressed oil from blanched (95±2°C for 3 min) and microwaved (261 W for 102 s) seed. The oil samples were evaluated with respect to oil yield, refractive index, yellowness index, oxidation indices (peroxide value, anisidine value, total oxidation value), total carotenoids content (TCC), total phenolic content (TPC), antiradical scavenging capacity (DPPH, and ABTS), and fatty acid composition. The results showed that solvent extraction, irrespective of pretreatment (blanching and microwaving), yielded higher oil varying from 19 to 20% (dry weight). Cold-pressed oil contained higher oxidation indices than solvent-extracted oil; nonetheless, the oil conformed to the Codex Alimentarius standard for unrefined oil (peroxide value <15 meqO2 kg^-1 oil). Irrespective of pretreatment, cold-pressed oil exhibited a higher concentration of TCC (1.2- to 1.3-fold), TPC (1.2- to 2.0-fold) and greater antiradical activity (1.6- to 2.0-fold) than solvent extracted oil. At the same time, solvent-extracted oil showed higher levels of punicic acid (75-78%), whilst cold-pressed oil exhibited higher levels of palmitic acid (9-10%), oleic acid (10-11%), and linoleic acid (17-20%). The principal component revealed that cold-pressed oil was associated with TCC, TPC, and antiradical activity, whereas solvent-extracted oil was correlated with oil yield and punicic acid. The findings suggest that cold-pressed oil may be a valuable raw material in formulating pharmaceutical, nutraceutical and functional foods, whilst the solvent extracted oil might be useful in developing cosmetic products.