Prediction of thymoquinone content in black seed oil using multivariate analysis: An efficient model for its quality assessment

Nigella sativa L. seeds are a rich source of diverse phytochemicals, well recognized for their medicinal properties. The seed oil (Black Seed Oil) is the more widely used therapeutic form and is readily adulterated. In this study, 30 commercial oil samples collected from different regions were assessed regarding their thymoquinone concentration using High Performance Liquid Chromatography. A discrepancy was shown in thymoquinone content ranging from 0.010 in one Saudi sample to 13.296 mg/g oil in one Egyptian sample. Ultra-violet spectroscopy was conducted on the methanolic extracts and multivariate analyses were applied to the collective data with Principal component Analysis (PCA) showing clear segregation of samples with high thymoquinone concentration positively clustered along PC1 (explaining 94% of the variance). This model allowed for the prediction of thymoquinone at correlation coefficients of 0.997 and 0.984 for the calibration and test set respectively verifying the robustness of the method. Lipid profiling of the oil samples was also conducted for quality verification. The model developed offers a simple, efficient and reliable method for the quality assessment of Black Seed Oil.