Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 2009
Publication Date: January 12, 2010
Citation: Glenn, G.M., Klamczynski, A., Wood, D.F., Chiou, B., Orts, W.J., Imam, S.H. 2010. Encapsulation of plant oils in porous starch microspheres. Journal of Agricultural and Food Chemistry. 58(7):4180-4184. Interpretive Summary: Starch is a common encapsulating media for food products and has also been used for encapsulating agricultural products because of its biodegradability in many agricultural environments and versatility in processing. More recently, there has been a concerted effort to replace synthetic herbicides and pesticides with natural control agents such as essential oils and to develop effective delivery systems. ARS researchers have developed porous particles in the same size range as pollen that can be loaded with pesticides from natural plant sources. The small particle size allows the particles containing the active ingredient to easily disperse and adhere to a host and provide local protection agains pests. Results of this work could help provide an effective control for agricultural pests.
Technical Abstract: Natural plant products such as essential oils have gained interest for use in pest control in place of synthetic pesticides because of their low environmental impact. Essential oils can be effective in controlling parasitic mites that infest honeybee colonies but effective encapsulants are needed to provide a sustained and targeted delivery that minimizes the amount of active ingredient used. The present study reports the encapsulation of essential oils in porous microspheres that are within the size range of pollen grains and can be easily dispersed. The microspheres were made by pumping an 8% aqueous high-amylose starch gelatinous melt through an atomizing nozzle. The atomized starch droplets were air-classified into two fractions and collected in ethanol. The size range for each fraction was measured using a particle size analyzer. The mean particle size for the largest fraction was approximately 100 ìm with a range from 5 ìm to over 300 ìm. Part of the reason for the large particle size was attributed to the merging of smaller particles that impinged upon each other before they solidified. The smaller fraction of spheres had a mean particle size of approximately 5 ìm. The starch-based porous microspheres were loaded with 16.7% (w/w) essential oils including thymol (5-Methyl-2-isopropylphenol), clove, origanum, and camphor white oil. The essential oils appeared to be largely sequestered within the pore structure since the spheres remained a free-flowing powder and exhibited little if any agglomeration in spite of the high loading rate. Furthermore, SEM micrographs verified that the pore structure was stable as evidenced by the persistence of pores in spheres that had first been loaded with essential oils and then had the oil removed by solvent extraction. Thermal gravimetric analyses were consistent with a loading rate at predicted levels.