Document Type : Research Article
Author
Department of Horticultural Science, College of Agriculture, Jahrom University, PO BOX 74135-111, Jahrom, Iran
Abstract
Introduction
Plant materials contain many bioactive compounds such as alkaloids, flavonoids, terpenoids, phenolic compounds, etc., which can be used to prepare health products, cosmetics, medicines, food additives, etc., and have great importance for improving human health and quality of life (Ahmadian et al., 2023). In recent years, the extraction of bioactive compounds from plant materials has attracted much attention. Extracting these active compounds is a challenging task because they are usually present in small amounts in plants and special techniques and methods are required for their successful isolation (Qin et al., 2022). Bioactive substances are usually found inside or between plant cells. The main resistance factor to the diffusion of bioactive substances into the solvent during extraction is the plant cell wall (Zhao et al., 2014). In order to improve extraction efficiency, pretreatments are usually performed before the extraction operation to destroy cell wall structure, increase cell wall permeability, and promote release of active substances (Ijod et al., 2022). Cold plasma has shown a wide application prospect in food processing, pharmaceutical and health care, environmental protection, biomedicine, and many other fields due to its many advantages such as low temperature, high efficiency, low energy consumption, and environmental compatibility (Melotti et al., 2021). When cold plasma is applied to plant materials, it can destroy the cell wall structure and increase the surface hydrophilicity of the materials, thereby improving the extraction efficiency (Keshavarzi et al., 2020). Therefore, it can be widely used as a pre-extraction treatment. Nevertheless, there is no comprehensive study on DBD cold plasma pretreatment technology to enhance the extraction of bioactive compounds from plant materials, which is suitable for researchers to continue their research. Therefore, the present study aimed to investigate the effect of cold plasma pretreatment on the extraction rate of active compounds from Origanum vulgare.
Materials and Methods
Oregano seeds were sown in the medicinal plant farm of Jahrom University in October 2023, and aerial parts of the plant was harvested in May 2024 at the flowering stage and dried in shade. After drying, the samples were subjected to DBD cold plasma pretreatment, with air as the carrier gas and different voltages and times. Then, essential oil extraction and extraction were performed on the pretreated samples, and some of the active substances such as essential oil content, total phenolic compounds, flavones and flavonols, total flavonoids, tannin contents, antioxidant activity, and total carbohydrates were measured. In this study, a factorial experiment was conducted in a completely randomized design with 3 replications. The first factor included time at three levels (0, 3, and 6 minutes) and the second factor included voltage at two levels (20 and 30 kV). For the pretreatment of the samples for essential oil extraction, 30 g of dried marjoram plant were hand-cut and crushed for each treatment, and then 30 ml of water was added to them, and then they were placed in a plasma device. After the treatments, the samples were extracted. Plasma pretreatment was applied to investigate its effect on the phytochemical compounds in the extract, as follows: the plant samples were powdered using an electric grinder, and then five g of the powdered sample was weighed for each treatment and 25 ml of 70% methanol solvent was added to them. After the powdered samples were completely mixed with the solvent, they were placed in a plasma device for plasma pretreatment. After the treatments, the samples were extracted.
Results and Discussion
The findings of this study showed that a voltage of 30 kV for 3 minutes was more effective in extracting the non-volatile active substances of oregano and led to an increase in all of their measured traits compared to the control treatment. Also, the lowest amount of active substances measured in this study was observed in the 30 kV treatment for 6 minutes. According to the results obtained from this study, it can be concluded that the duration of plasma pretreatment has a greater effect than the output voltage on the extraction of non-volatile active ingredients. So that in this study, using a voltage of 30 kV for 3 minutes led to an increase in the active substances of oregano, while using the same voltage for 6 minutes led to the opposite result. Although the effect of plasma pretreatment on the extraction of essential oil was not significant. However, the highest amount of essential oil was measured in the control treatment and the lowest amount was in the 30 kV voltage treatment for 3 minutes, indicating the destruction of essential oil glands and loss of essential oil at this voltage. At present, the mechanism of cold plasma treatment to improve the extraction efficiency of active substances is not fully understood, but it is generally believed that it can be attributed to two possible mechanisms: the decomposition of cell wall structure and increase of surface hydrophilicity. Disruption of plant cell wall structure can reduce diffusion resistance of active substances, thereby promoting their release. Meanwhile, increase of surface hydrophilicity of materials facilitates the dissolution and diffusion of hydrophilic active substances, thereby improving the extraction efficiency (Bao et al., 2020a; 2020b).
Conclusion
The findings of this study showed that a voltage of 30 kV for 3 minutes was more effective than other treatments in extracting non-volatile active ingredients of oregano and led to an increase in all measured traits compared to the control treatment. While the effect of plasma treatments on the extraction rate of essential oil was not significant.
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