Effect of refining on the quality of oils extracted by cold press from black cumin (Nigella sativa L.) seed and by solvent from its cake

Black cumin seed oil, known for its bioactive compounds and health benefits, faces challenges due to its high peroxide value and free fatty acid content, limiting its applications. The study investigates oil extraction from black cumin seeds using cold pressing and solvent extraction. The oil extraction yields were found to be 32% from the seeds and 13% from the cake. Subsequently, the study investigated the impact of different refining steps on the quality of these oils. The oil extracted from the cake exhibited higher free fatty acid, chlorophyll, and carotenoid contents compared to the oil extracted from the seeds, with increases of 84%, 73%, and 66%, respectively. Conversely, the peroxide value, total phenol, and thymoquinone content of the cake-derived oil were lower than those of the seed-derived oil, with reductions of 74%, 69%, and 95%, respectively. The refining process resulted in general reductions in peroxide value, free fatty acid, and p-anisidine levels. However, no significant effect on the fatty acid composition was observed. The refining led to a decrease in the bioactive content, including total phenolic compounds (6%-68%), carotenoids (86%-85%), and thymoquinone (50%-90%). These results contribute to a better understanding of the potential applications and refining requirements for black cumin seed oil.