Effects of black seed oil combined with olive oil or honey on antioxidant activities, phenolic content, and identification and quantification of thymoquinone, a key bioactive compound

The plant Nigella sativa (NS) has a rich history in folk medicine, being utilized for various illnesses and as tonic drugs. Furthermore, thymoquinone (TQ), a major compound found in the seeds of NS, may exhibit antioxidant activity. In addition to black candles, traditional medicine employs olive oil and honey to nourish the body. Some folk medicine systems combine NS, honey, and olive oil for improved efficacy; however, knowledge regarding the antioxidant properties of black seed oil (BSO), BSO with olive oil (BSOO), and BSO with honey (BSOH) remains limited. Therefore, in this study, we investigated the antioxidant properties of BSO, BSOO, and BSOH. Gas chromatography-mass spectrometry analysis showed that BSO contained 73.48 ± 1.23 mg/kg TQ. BSO, BSOO, and BSOH exhibited remarkable antioxidant activity, with NO scavenging activities of 94.32, 76.53, and 50.37, respectively. The 2,2-diphenyl-1-picrylhydrazyl and metal chelating activity assays (with half-maximal inhibitory concentration values), oxygen radical antioxidant capacity, and total flavonoid compound content of BSO were 0.135 ± 0.003 mg/mL, 0.005 ± 0.003 mg/mL, 32 ± 0.4 μM Trolox/g extract, and 997 ± 20 mg catechin equivalent/g of extract, respectively. These results are potentially linked to the increased antioxidant activity, as suggested by Pearson's correlation coefficients. In the ferric-reducing antioxidant power assay, the highest antioxidant activity was demonstrated by BSOO and BSOH, with total phenolic content of 7288 ± 300 mM FeSO4/mg and 346 ± 17 mg of gallic acid equivalent/g E, respectively. This study affirms the potent antioxidant properties of BSO, BSOO, and BSOH, emphasizing the importance of further research on NS infusion as a promising antioxidant agent and its application as an anti-aging and tonic drug.