Edible Nanoemulsions as Carriers of Active Ingredients: A Review

Abstract

There has been growing interest in the use of edible nanoemulsions as delivery systems for lipophilic active substances, such as oil-soluble vitamins, antimicrobials, flavors, and nutraceuticals, because of their unique physicochemical properties. Oil-in-water nanoemulsions consist of oil droplets with diameters typically between approximately 30 and 200 nm that are dispersed within an aqueous medium. The small droplet size usually leads to an improvement in stability, gravitational separation, and aggregation. Moreover, the high droplet surface area associated with the small droplet size often leads to a high reactivity with biological cells and macromolecules. As a result, lipid digestibility and bioactive bioavailability are usually higher in nanoemulsions than conventional emulsions, which is an advantage for the development of bioactive delivery systems. In this review, the most important factors affecting nanoemulsion formation and stability are highlighted, and a critical analysis of the potential benefits of using nanoemulsions in food systems is presented.

Nanoemulsions: Synthesis, Characterization, and Application in Bio‐Based Active Food Packaging

“…High‐speed mixing emulsification apparatuses work under similar principles, but they are mostly not appropriate as a sole mechanism for nanoemulsion elaboration; with some exceptions (Burapapadh, Kumpugdee‐Vollrath, Chantasart, & Sriamornsak, ) by using high‐speed mixers, for example, Ultra‐Turrax, droplets usually do not reach homogeneous nanodimensions. According to Salvia‐Trujillo, Soliva‐Fortuny, Rojas‐Graü, McClements, and Martín‐Belloso (), high‐energy methods are more suitable for the elaboration of nanoemulsions intended for food‐related applications, because they allow the use of natural/nontoxic emulsifiers at lower concentrations, they ease industrial‐scale production, and the required equipment is commercially available.…”

“…Additional potential benefits, at optimized conditions, are good dispersion stability, requirement of relatively low emulsifier contents, and low risk of microbial contamination upon processing (Abbas et al., ). Apart from scaling‐up limitations, there are other drawbacks of sonication for nanoemulsion fabrication, including the occurrence of hotspots and cavitation‐induced degradation processes that may be detrimental for labile compounds (Chemat, Grondin, Shum Cheong Sing, & Smadja, ; Salvia‐Trujillo et al., ), as well as the risk of metal ion release into the emulsion due to cavitation‐induced abrasion of the sonication probe (Freitas, Hielscher, Merkle, & Gander, ).…”

“…As to treatment time, it has a great influence on droplet size and size distribution, the optimal period varying from a few seconds to several minutes. The typical behavior is that increasing the time will decrease droplet diameter to an equilibrium value, after which processing for longer periods either has no influence or has detrimental effects (Leong, Wooster, Kentish, & Ashokkumar, ; Salvia‐Trujillo et al., ; Tang, Shridharan, & Sivakumar, ). Droplets as small as 4 to 5 nm have been reported (Salvia‐Trujillo et al., ).…”

“…The typical behavior is that increasing the time will decrease droplet diameter to an equilibrium value, after which processing for longer periods either has no influence or has detrimental effects (Leong, Wooster, Kentish, & Ashokkumar, ; Salvia‐Trujillo et al., ; Tang, Shridharan, & Sivakumar, ). Droplets as small as 4 to 5 nm have been reported (Salvia‐Trujillo et al., ). Sonication power is probably the main control parameter, and it is usually set for a given system by optimization procedures; increasing sonication power reduces substantially the sonication time until no further effect is exerted (Cucheval & Chow, ; Delmas et al., ).…”

“…For instance, a higher temperature means a lower surface tension and, thus, less energy is required to achieve minimum dimensions, but it also entails reduced acoustic wave intensities. As mentioned above, increased microlocated temperature during sonication can damage susceptible nanoemulsion components, including heat‐sensitive bioactive compounds (Abbas et al., ; Salvia‐Trujillo et al., ). Therefore, controlling the temperature, by manipulating process parameters and/or by using cooling systems, is considered crucial.…”