Optimization of ultrasound-assisted extraction of Nigella sativa seed oil for enhancement of yield and antioxidant activity

The seeds of Nigella sativa have been shown to contain a number of constituents that have nutritional and therapeutic characteristics. The oil extracted from the seeds of Nigella sativa has been traditionally used in food systems with reference to its medicinal properties. The different bioactive compounds present in the Nigella sativa seed oil consist of polyphenols which offer a fair amount of antioxidant activity to the oil. Most of these bioactive compounds are generally heat sensitive and prone to oxidation. During the processing and storage, there is loss of antioxidant activity of the oil and the associated bioactivity. This occurs primarily due to the effects of temperature and other environmental factors during processing and storage. Under this background, this study was undertaken with the aim of extracting the Nigella sativa seed oil in order to ensure the improved retention of antioxidant and bioactive characteristics in the essential oil. The extraction of Nigella sativa seed oil was carried out using ultrasound-assisted extraction technique using hexane as solvent. The process was optimized using response surface methodology in order to enhance the yield and antioxidant activity of the extracted Nigella sativa seed oil. The effect of different processing parameters was evaluated on the yield and antioxidant activity. The process variables included the extraction temperature, extraction time and solvent concentration. It was observed that all the factors had significant effect on the yield and antioxidant activity of the extracted Nigella sativa oil. The optimized conditions for maximizing the yield and antioxidant activity obtained were a solvent concentration of 42.82 mL/5 g of sample, the extraction temperature of 69.09 °C and extraction time of 86.60 min, which were validated and found close to the experiment values. Under this set of conditions, the yield was maximized to 34.53% with enhanced antioxidant activity, having IC 50 value of 203.56 µg/mL. Article Highlights Cavitation induced by ultrasound enhanced mass transfer and facilitates release of phytocompounds. Ultrasound assited extraction of Nigella sativa oil at lower temperatures preserved heat sensitive compounds. Nigella sativa oil mainly contains thymoquinone, thymohydroquinone, and thymol.