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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 gramnegative 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.

Milk and dairy products represent an important part of functional food in the market. Based on their positive health and nutritional benefits, they have gained popularity and their consumption as well as production is on the rise in the last few decades. As a result of this trend, milk-based products are being used for the delivery of bioactive food ingredients. This study is devoted to the formulation of stable emulsions containing grape seed oil dispersed with several emulsifiers (Tween 80, monocaprylin, and lecithin) in milk. Photon correlation spectroscopy was used to evaluate the characteristics of the emulsions in terms of mean droplet size, droplet size distribution and polydispersity index. Emulsions were prepared using 2% and 5% w/w grape seed oil, and 3%, 5%, or 8% w/w emulsifier, and these were homogenized at two different rates of 1050 and 13400 rpm. Parameters influencing emulsion particle size and particle size distribution were identified, which included emulsifier type, its HLB value, oil type (virgin, refined), homogenization rate and the fat content in the milk. Homogenization at 13400 rpm for 10 min. produced fine emulsions with small mean particle sizes and monomodal distribution of droplets. Regarding emulsifier type, the smallest droplet sizes were obtained with formulations containing Tween 80 (250-315 nm), whereas lecithin primarily accounted for the monomodal particle size distributions.