Application of novel technologies such as microwave and pulsed electric fields (PEF) might increase the speed and efficiency of oil extraction. In the present research, PEF (3.25 kV/cm electric field intensity and 30 pulse number) and microwave (540 W for 180 s) pretreatments were used to study the process of oil extraction from black cumin (Nigella sativa) seeds. After applying the selected pretreatments, the oil of seeds was extracted with the use of a screw press and the extraction efficiency, refractive index, oil density, color index, oxidative stability, and chemical components of oil and protein of meal were evaluated. The achieved results expressed that PEF and microwave pretreatments increased the oil extraction efficiency and its oxidative stability. Different pretreatments didn't have any significant influence on the refractive index of black cumin seed oil (p>.05). When microwave and PEF were used, the oil density showed an enhancement as the following: 1.51% and 0.96%, respectively in comparison with the samples with no pretreatments. Evaluation of the extracted oils, using GC/MS analysis indicated that thymoquinone was the dominant phenolic component in the black cumin oil. Finally, the SEM analysis revealed that microwave and PEF can be useful in the extraction of oil from black cumin seeds since these treatments damaged cell walls and facilitated the oil extraction process.
Background: In the present study, the effects of ultrasound pretreatment parameters including irradiation time and power on the quantity of the extracted phenolic compounds quantity as well as on some selected physicochemical properties of the extracted oils including oil extraction efficiency, acidity and peroxide values, color, and refractive index of the extracted oil of black cumin seeds with the use of cold press have been studied. Methods: For each parameter, three different levels (30, 60, and 90 W) for the ultrasound power and (30, 45, and 60 min) and for the ultrasound irradiation time were studied. Each experiment was performed in three replications. Results: The achieved results revealed that, with enhancements in the applied ultrasound power, the oil extraction efficiency, acidity value, total phenolic content, peroxide value, and color parameters increased significantly (P < 0. 01). Enhancements in ultrasound irradiation time have not significantly increased the oil extraction efficiency, acidity value, total phenolic content, and peroxide value as well as the oil refractive index (P < 0.05). As the highest oil extraction efficiency (39.93%) was obtained from the seeds when the applied ultrasound power and time were 90 W and 60 min respectively, and the lowest acidity value of oil was achieved once the applied power and time of ultrasound were 30 W and 30 min respectively. The application of ultrasound as pretreatment has not shown any significant effects on the refractive index of the extracted oils (P > 0.05). Conclusions: In summary, it could be mentioned that the application of ultrasound pretreatment in the oil extraction might improve the oil extraction efficiency, the extracted oil's quality, and the extracted phenolic compounds content.
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