Combined spectroscopic and chromatographic techniques augmented with chemometrics for the authentication of black cumin (Nigella sativa L.) seed oil

Abstract

Edible oils adulteration has a great concern because of its health and economical effects. Black cumin seed oils (BCSOs) are one of the most adulterated edible oils. In this case, the purpose of this research was to investigate authenticity of commercial BCSOs by spectroscopic and chromatographic techniques combined with orthogonal partial least square-discriminant analysis (OPLS-DA) and hierarchical cluster analysis (HCA). Sixteen commercial BCSO samples (100 % pure-certified and other BCSOs), potential blending oils (sunflower, corn, and soybean oils), and twenty-one synthetically adulterated BCSO samples blended with sunflower (SFO), corn (CO), and soybean (SBO) oils at levels of 5 %, 10 %, 15 %, 20 %, 30 %, 40 %, and 50 % (v/v) were analysed. Screening of potential fingerprinting markers such as thymohydroquinone (THQ), thymoquinone (TQ), carvacrol (CRV), tocopherol isomers (α-, γ-, and δ-), as well as total antioxidant capacity and phenolic content analysis were carried out utilizing spectrophotometric CUPRAC, ABTS, and Folin Ciocalteu’s assays. Commercial pure and fraudulent BCSOs and synthetically adulterated samples were successfully classified in OPLS-DA graphs with 95 % confidence level. Even to five percent detection limit for SFO, CO and SBO adulteration were prominently monitored. In consequence, the proposed spectroscopic and chromatographic methods seem to be a practically applicable, sensitive and versatile protocol that can be used as an alternative fingerprinting procedure to determine adulteration of commercial BCSOs.