Enhanced Thymoquinone Recovery from Cold-Pressed Black Seeds (Nigella sativa L.) through Freeze-Thaw and Microwave Pretreatment Techniques

The quality of black seed oil depends greatly on the extraction method used. Traditional methods like cold pressing are valued for producing high-quality oil that retains its natural nutrients and flavor. However, these methods often come with a trade-off, as they tend to yield less oil and lower levels of bioactive compounds, making them less efficient for large-scale production. To overcome these limitations, seed pretreatment techniques were investigated. In this study, black seeds were subjected to freeze-thaw and microwave pre-treatment before cold pressing to increase the content of thymoquinone, which is a key bioactive compound in black seeds. For the freeze-thaw treatment, black seeds were frozen at -17 °C for 24 and 48 h, followed by thawing at 50 °C for 1 h. This process was repeated for 1, 2, and 3 cycles. Microwave treatment involved subjecting seed samples to microwave at a frequency of 2450 MHz and power levels of 400 W and 640 W for durations of 1, 2, and 3 min. Subsequent oil extraction was performed by using cold pressing. HPLC analysis showed a significant increase in thymoquinone content with freeze-thawed seeds (for 48 h and 3 cycles) showing a remarkable increase like 79.93% according to untreated black seeds. Microwave-pretreated seeds at 640 W for 3 min exhibited more than double thymoquinone content compared to untreated seeds. Other quality parameters, including moisture, specific gravity, acidity, peroxide value, and iodine value, shows comparable characteristics, while significant enhancing the sensory analysis of the pretreated oil (p < 0.05). These findings suggest that freeze-thaw and microwave pretreatments can serve as innovative methods for enhancing thymoquinone levels in Indian black seed oil, providing a promising avenue for improving the overall quality of this valuable natural product.