Spontaneous microencapsulation of geraniol by zein

Abstract

Geraniol was successfully micro-encapsulated with zein in a one-step phase separation process in which the zein and geraniol were both initially dissolved in a water-ethanol mixture. Microcapsules were only formed at geraniol-to-zein mass ratios above unity. This is ascribed to the relative solubility of the oil and protein in the solvent at the point of incipient phase separation: The geraniol must phase separate first before zein precipitation commences. The resultant oil droplets subsequently provide the interfacial surfaces that act as nucleation sites for the precipitation of the amphoteric zein molecules on continued dilution with water. The near spherical microcapsules formed under these conditions, comprised a foamed closed-cell wall that enclose large internal cavities in which the geraniol was trapped. The highest particle yield, 85.3%, and oil encapsulation efficiency, 83.5%, were obtained at a geraniol to zein mass ratio of 3:1. The particle size distribution for this system was log-normal with d10, d50 and d90 values of 10, 32 and 88 μm respectively. The temperature dependent geraniol release rate from these capsules followed power law kinetics with a release exponent of 0.80.