Quality of oil extracted by cold press from Nigella sativa seeds conditioned and pre-treated by microwave

Abstract

Black cumin (Nigella sativa) seed (BS) oil has received much interest in the food and pharmaceutical industries due to its valuable nutritional properties, but this oil has low oxidative stability. The effect of microwave pre-treatment at 0 to 2.5 min and conditioning with different buffers at pH 3 to 9 of BS, before oil extraction by cold press, were investigated. The oil extraction yield was higher; acid value (AV) and peroxide value (PV) were lower in the oil extracted from seeds, which were first microwaved and then moisturized and vice versa. BS with pH 3, microwave time of 1.25 min, and moisturizing level of 5%, which gave oil extraction yield of 27.2%, AV of (2.9 mg NaOH/g oil), and PV of (8.3 meq O2/kg oil), was selected as an optimum sample and its quality changes were investigated during storage compared with the oil extracted from the control sample (without any pre-treatment). In conclusion, the oil extracted from the pre-treated BS had higher bioactive components and lower AV and PV during the storage; therefore, microwave radiation and pH adjustment before oil extraction from BS by cold press are recommended.