The oily substance with an aromatic smell obtained by extracting and separating from plants is called volatile oil, also known as plant essential oil. In recent years, more and more research has focused on the antibacterial effects of volatile oil. By using ultrasonic extraction to obtain volatile oil from mugwort leaves and turmeric, it was found that this volatile oil can inhibit pathogenic bacteria such as Staphylococcus aureus, Escherichia coli, and Staphylococcus epidermidis. In addition, the volatile oil of Forsythia suspensa has a more extensive antibacterial effect, and the volatile oil from Forsythia suspensa from different origins can also inhibit bacteria. Research has discovered that the main compound components in the essential oil are the key to exerting antibacterial activity, such as thymol and carvacrol in thyme essential oil, eugenol in cinnamon essential oil, eugenol in perilla essential oil, cinnamaldehyde in patchouli, cinnamon essential oil, and various anthraquinone substances in safflower essential oil. The above experimental results reflect the antibacterial effect of volatile oil in a single plant extract. Another way is to mix plant essential oil with sodium butyrate to study its synergistic antibacterial effect. The results show that compared with only adding volatile oil, the mixture enhances the inhibitory effect on Escherichia coli, but has no effect on lactobacilli.
The volatile oil extraction methods of safflower can also be processed using steam distillation and supercritical CO2 fluid extraction. The results of in vitro antibacterial tests show that the safflower essential oils obtained by both methods have broad-spectrum antibacterial properties. Compared with Gram-negative bacteria, the safflower plant essential oil has better damage and antibacterial effects on Gram-positive bacteria, thereby inferring the antibacterial mechanism of the essential oil: as the volatile oil acts on the bacterial cell membrane for a longer time, it gradually enhances the permeability of the cell membrane, resulting in the leakage of intracellular sodium, potassium, and calcium ions, an increase in cell conductivity, and bacterial death. Through scanning electron microscopy, it can be observed that the safflower essential oil also acts on the cell membrane of Escherichia coli, causing varying degrees of rupture of the smooth surface of the Escherichia coli cell membrane, changing the permeability of the cell membrane, and causing the leakage of intracellular proteins and the release of potassium ions, thereby causing the death of Escherichia coli. The reason for the rupture of the cell membrane may be that the safflower essential oil affects the formation of pores on the cell membrane surface, causing damage to the cell membrane, and the cell membrane damage becomes more obvious as the concentration of safflower essential oil increases.
The antibacterial mechanism of the camellia flower essential oil includes three aspects: On the one hand, it can damage the cell structure, not only having the similar damage effect on the cell membrane of harmful bacteria as safflower and cinnamon essential oils, but also having the damage effect on the structure and function of the cell wall of harmful bacteria, causing the leakage of nucleic acids; On the other hand, it can prevent the formation of new biofilms by reducing the biomass and cell activity of the biofilm, thereby destroying the pre-formed biofilm; In addition, the bacterial surface hydrophobicity test indicates that the safflower essential oil can reduce the adhesion ability of the bacterial strain. The specific pathways of these antibacterial mechanisms are still unclear and need further exploration.
