Liposomal and free essential oil of rosemary as antifungal and antibacterial agent in salad dressing

Natural preservatives are a suitable alternative to chemical preservatives in the food industry. To overcome its hydrophobic nature, insolubility in water, and degradation of free essential oils, liposomal encapsulation can be applied. In this study, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of free as well as liposomal rosemary essential oils (REO) were measured using disk diffusion and serial dilution method for Escherichia (E.) coli, Staphylococcus (S.) aureus, Salmonella (S.) enterica, Lactiplantibacillus (L.) plantarum, Aspergillus (A.) niger, and Saccharomyces (S.) cerevisiae. The antimicrobial properties of free and encapsulated essential oils were compared with sodium benzoate during thirty days of storage. Also, the release pattern of REO from liposomes was studied using dialysis membranes during the 30 days of storage. The results showed that the MIC of free and encapsulated REO is in the range of 3.5–5% and 5–6.5%, respectively. Gramþ Staphylococcus aureus was identified as the most sensitive, while Escherichia coli was the most resistant among the tested microorganisms to the essential oils. During refrigerated storage, free REO and sodium benzoate did not show any significant difference in antimicrobial properties (P > 0.05), while encapsulated REO significantly reduced the number of microorganisms in stored salad dressing (P ≤ 0.05).