Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: August 8, 2008
Publication Date: September 9, 2008
Citation: Parris, N., Cooke, P.H., Moreau, R.A., Hicks, K.B. 2008. Encapsulation of essential oils in zein nanosperical particles. Book Chapter in New Delivery Systems for Controlled Drug Release from Naturally Occurring Materials, ed. by N. Parris, L. S. Liu, C. Song, and V. P. Sastri, ACS Symposium Series 992, American Chemical Society, Washington, DC pp 175-192. Technical Abstract: Essential oils, oregano, red thyme, and cassia (100% pure oil), were encapsulated by phase separation into zein particles. Typical yields were between 65% and 75% of product. Encapsulation efficiency of all oils was 87% except for cassia oil which was 49%. Loading efficiency of all oils was 22% except for cassia oil which was 12%. Topographical images indicated that the powders were made up of irregularly shaped particles (~50 um) containing close-packed nanospheres. Approximately 31% oregano encapsulated nanospheres, had mean diameters greater than 100 nm compared to 19% for the zein alone nanospheres. Examination of the zein-oregano oil and zein alone powder particle surfaces by scanning electron microscopy and atomic force microscopy revealed areas of close-packed spheres. Efforts to localize oil in powder particles by fluorescence from Nile Red stain using confocal laser scanning microscopy were equivocal because the zein particles fluoresced at equal intensities as the zein-oregano oil powdered particles. Enzymatic in vitro digestion of zein particles with pepsin at a concentration ratio of 10:1 was complete after 52 h in phosphate-citrate buffer, pH 3.5, at 37 degrees C. However, less than half the particles were digested after 4 h, the typical gastric emptying time for humans and some monogastric animals. Nonenzymatic, aqueous in vitro release of essential oils from encapsulated zein particles was carried out in phosphate buffered saline at pH 7.4 and 37 degrees C. Very little oregano oil appeared to coat the particle surface because no initial burst of oregano was released which indicated that the oregano oil is encapsulated or entrapped within the particle. Release occurred at varying rates over 20 h probably from different locations within the closely packed nanospheres of different sizes. Gel electrophoresis SDS-PAGE of zein incubated with freeze-dried swine manure solids at 37 degrees C indicated that preformed microbial enzymes capable of digesting zein within minutes were present in the manure. Except for differences in size of nanospheres, no structural differences were resolved by several microscopic distribution methods, suggesting that the oil and protein phases were blended during phase separation.