Nanoemulsions containing essential oils: characterization and antimicrobial activity against food contaminating bacteria

Abstract

The food industry, driven by growing consumer demand for healthier foods and free of synthetic additives, is looking for new preservative options. In this sense, essential oils (EOs) have great potential because they have been studied for some time due to their antioxidant and antimicrobial activity. Although essential oils have biological activity against different microorganisms, their use in food is still a challenge. EOs have low water solubility and incorporation into food is difficult. Moreover, their use may lead to change in taste and flavor in food products. In this way, nanoemulsions of essential oils have been extensively studied. The objective of this work was to prepare and characterize nanoemulsions containing essential oils and to verify their effectiveness against food contaminating bacteria. First, nanoemulsions of oregano, thyme, clove and lemongrass were elaborated with Tween 80. They were evaluated for the influence of pH, temperature and ionic strength on physical stability through particle size and zeta potential. Nanoemulsions were also evaluated for antimicrobial activity against endospores and vegetative cells of C. sporogenes. The results showed that the physical stability of nanoemulsions is dependent on the type of essential oil and initial particle size, as well as temperature and pH. The use of salt influenced only the electrostatic repulsion of the droplets. Moreover, it was possible to observe improved sporicidal action of nanoemulsions when compared to free essential oils, synergism and reduced growth of C. sporogenes vegetative cells. In a second experiment, nanoemulsions containing oregano and lemongrass essential oils were made with protein, pectin, and protein-pectin complex as surfactants. They had their

antimicrobial potential evaluated against Escherichia coli. Nanoemulsions made using protein- pectin complex were more stable with storage time. In this study it was observed that the

difference in interfacial tension between the surfactants used affected the activity of nanoemulsions against E. coli. In both studies it is evident that the composition of the essential oil affects the antimicrobial activity of nanomeulsions. In addition, it is concluded that the use of different surfactants impacts on droplet size and nanoemulsion stability as well as activity against microorganisms.