Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/13/2005
Publication Date: 6/15/2005
Citation: Parris, N., Cooke, P.H., Hicks, K.B. 2005. Encapsulation of essential oils in zein nanospherical particles as a delivery system for antimicrobials. Journal of Agricultural and Food Chemistry. V.53,No.12,p.4788-4792 Interpretive Summary: The development of new antimicrobial compounds is of great importance because of the rapid evolution of bacteria that are resistant to multiple drugs due to overuse of antibiotics in humans and livestock. Essential oils have been shown to inhibit the growth of harmful bacteria, yeast, fungi and have been proposed as substitutes for antibiotics in animal feeds. In many instances, in order to obtain the desired inhibition, an excess of oil is required which results in poor economics and a number of undesirable effects. In this study we investigated the encapsulation of essential oils into extremely small zein-coated particles as a controlled delivery system to maximize their antimicrobial properties and minimize interactions with other components in the feed. We designed experimental procedures to simulate digestion of the zein particles in the stomach and slow release of the oils in the intestines. Results indicated that digestion of zein particles with pepsin (a digestive enzyme) was complete after 52 h and release of essential oils from the encapsulated particles occurred at different rates over 20 h depending on the location of the oil in the zein particles. Since these particles could be useful for oral or injectable administration they can be added to the feed or injected directly into the animal. Farmers and veterinarians should find application of the essential oils in this form to be easier to handle, less wasteful and hence more economical to use as a potential substitute for traditional antibiotics to prevent common intestinal infection in livestock.
Technical Abstract: Three essential oils, oregano, red thyme and cassia (100% pure oil) were encapsulated, by phase separation, into zein nanospherical particles. SEM images indicated that the powder was made up of irregular shaped particles (50 um) containing closely-packed nanospheres. Approximately 31% of the oregano encapsulated particles had mean diameters greater than 100 nm compared to 19% for the zein alone particles. In vitro digestion of zein particles with pepsin, at a ratio of 10:1, was complete after 52 h in phosphate-citrate buffer, pH 3.5 at 37 C by spectroscopic analysis. Non-enzymatic, aqueous in vitro release of essential oils from encapsulated zein particles was carried out in phosphate buffered saline at pH 7.4 and 37 C. Release occurred at varying rates over 20 h probably due to the release of oil from different locations within the closely packed nanospheres that had different rates of release. Use of different electron microscopic techniques, to locate oil rich regions around or within nanospheres was not successful, however.