H. Chen, Q. Zhong
University of Tennessee,
Keywords: microemulsions, formulation, food bioactives, antimicrobials, bioactivity, stability
Summary:Microemulsions as delivery systems of bioactive compounds have advantages of the long shelf-life stability, the ability to dissolve both hydrophilic and lipophilic compounds, and relative ease of preparation and application. When compared with nanoemulsions and conventional emulsions, microemulsions are thermodynamically stable at defined conditions and are optically isotropic liquid mixtures of oil, water, and amphiphiles. The structures in microemulsions typically have a dimension smaller than 50 nm. The preparation of microemulsions usually requires low mechanical energy but a large amount of surfactants to dissolve the discontinuous phase. Short-chain alcohols are commonly used as co-surfactants to reduce the interfacial tension to facilitate microemulsion formation but are limited in food applications. Because microemulsions are formed only at a certain set of compositional and environmental conditions, several recent systems remaining as microemulsions after infinite dilutions are reviewed because of their practical significance for food, pharmaceutical, and cosmetic products. An appropriate blend of surfactants can be used to tailor the hydrophile-lipophile balance of surfactants to enhance the oil phase loading. Such examples include blending lecithin with sucrose octanoate ester or Tween 20 to increase the loading of essential oils in microemulsions. Blending soybean oil containing long-chain triacylglycerols with essential oils is another strategy to change the polarity of the lipid phase and the affinity with surfactants so as to enlarge the one-phase regime of microemulsions. As delivery systems, microemulsions of essential oils can be used as wash solutions or loaded in biopolymer films. Microemulsion components have significant impacts on antimicrobial activities of essential oils, and the extent of impacts is dependent on the composition of essential oils. The oil phase of microemulsions can also be studied as delivery vehicles of lipophilic bioactive compounds of food origins, including curcumin, co-enzyme Q10, and beta-carotene. For food applications, impacts of microemulsion composition on stabilizing bioactive compounds are critical during shelf storage, and surfactants and oil phases with antioxidant properties can be adopted to stabilize bioactive compounds against UV and thermal degradation. Also will be discussed include the enhanced anticancer activity of lipophilic bioactive compounds dissolved in microemulsions. These recent studies demonstrate promising applications of microemulsions to improve the safety and healthfulness of food supplies.