Physicochemical properties and stability of black cumin (Nigella sativa) seed oil as affected by different extraction methods

Black cumin (Nigella sativa) oil (BCO) was recovered using different extraction techniques including solvent free system (cold-pressing) and solvent extracted systems (Soxhlet and microwave assisted). Oils were analyzed for the composition of fatty acids and bioactive compounds (sterols, tocopherols, chlorophyll, carotenoid and phenolics profile) and for some physicochemical properties [free fatty acid, peroxide value (PV), refractive index, and ultraviolet (UV) absorption at K-232 and K-270]. Antiradical power (AP) of oils was also evaluated, wherein cold-pressed oil had stronger AP than solvent extracted oils. Phenolic profiles analyzed by HPLC revealed that thymoquinone was the main phenolic compound wherein high levels of benzoic and p-hydroxy benzoic acids were found in cold pressed-BCO. Oxidative stability (OS) of oils was evaluated during accelerated oxidation conditions (oven test at 60 degrees C and Rancimat test at 110 degrees C). The greatest induction period was 19.6h for Soxhlet-extracted BCO, and the lowest induction period was 3.48 h for cold-pressed BCO. PV of cold-pressed BCO reached 85.3 meq O-2/kg oil, while PV of the other extracted oils were under 27.0 meq O-2/kg oil at the end of storage period. (C) 2014 Elsevier B.V. All rights reserved.