Antibacterial activity of stable 1‐monoacylglycerol (1‐MAG) microemulsions (MEs) of capric (C10:0), undecanoic (C11:0), lauric (C12:0), and myristic (C14:0) acids against the growth of gram‐positive and gram‐negative bacteria was tested and their inhibition effect was compared to that of neat 1‐MAG. To reveal their behavior with respect to eukaryotic cells, the cytotoxicity on mouse fibroblasts was also determined. The MEs were studied via pseudo‐ternary phase diagrams in order to find out the miscibility areas of all components used. The results indicated that at 1‐MAG concentrations of 1000–1900 mg/L, an inhibition of gram‐negative strains was improved compared to neat 1‐MAG and depended on the fatty acid type; however, at lower 1‐MAG concentrations, both systems showed comparable effect. The opposite trend was detected on gram‐positive bacteria, where 1‐MAGs showed better performance compared to corresponding MEs. The best antibacterial activity against both bacterial types was observed in 1‐MAG C12:0 MEs. MTT assay revealed significant cytotoxicity of all MEs. The threshold of 10 mg/L was determined as the limit for moderate toxicity, which represents 40–60% cell survival. All prepared MEs were transparent, stable during the storage period of 6 months and their particle sizes were between 15 and 20 nm. Practical applications: 1‐MAGs belong to safe and efficient antimicrobial agents and their application may be a convenient alternative to usage of synthetic antimicrobials; however, one of their limitations for certain applications is their insolubility in aqueous systems. This drawback can be reduced by encapsulation of 1‐MAGs in suitable ME system. The presented study has confirmed that 1‐MAG MEs possess suitable inhibitory activity against both gram‐negative and gram‐positive bacteria. Efficacy of MEs against gram‐negative strains was enhanced compared to 1‐MAG alone. Although the growth of gram‐positive bacteria was less affected by MEs when compared to neat 1‐MAG, the results can be closely related to potential industrial applications of the MEs as effective agents for cosmetics, dermatology, food industry, paint or coatings where water‐based systems are frequently used and desired. The application of studied systems might be to some extent limited due to the potential health risk caused by the observed cytotoxicity.
Formation and stability of n-undecane in water nanoemulsions prepared by EIP method (Emulsion Inversion Point) in the presence of two nonionic surfactants were studied. In the study, the influences of surfactant concentration, HLB value and oil-to-water ratio on the particle size and distribution were investigated. The stability of emulsions was evaluated from changes in particle size distribution determined by photon correlation spectroscopy, and by visual and microscopy description of their appearance. The results obtained indicate that all the above mentioned variables significantly influence particle size and distribution. It is obvious that for given oil phase, the optimum HLB value of 10.5 exists, at which the emulsion particle size is the smallest at all studied oil-to-water ratios (5/95, 10/90, 15/85, 20/80, 25/75, 30/70). The HLB values above and below optimum then induce the increase of particle size of the studied emulsions. The best emulsion stability was observed for samples stored at the temperature of 4 °C.
