Optimization of yield and thymoquinone content of screw press-extracted black cumin seed oil using response surface methodology

Because there have been no previous reports on the use of screw presses for black cumin (Nigella sativa L.) seed oil extraction, the present study examined the effects of feed rate, temperature, and moisture content on the yield and thymoquinone content of mechanically extracted cold-pressed black cumin seed oil. The extraction parameters were optimized using a Box–Behnken design. Optimal conditions were identified by superimposing the response surfaces of oil yield and thymoquinone content. The thymoquinone content was stable under extraction conditions of 60 °C. Moisture played an important role in both oil yield and thymoquinone content. A maximum oil yield of 31.67 wt% ± 0.85 wt% was obtained at a feed rate of 45 g/min, temperature of 70 °C, and moisture content of 6 wt%. However, a low thymoquinone content of 5.14 ± 0.74 mg/mL was observed under these conditions. Furthermore, high thymoquinone content (∼12.00 mg/mL) reduced the oil yield to 10–13 wt%. The optimal conditions were found to be a feed rate of 50–54 g/min, moisture content of 15–18 wt%, and temperature of 55–60 °C, which gave a yield of 22 wt% oil and 10 mg/mL thymoquinone content.