The role of a moisture-barrier latex in controlling retention, stability and release of D-limonene from complex coacervated matrix microparticles formed during spray drying

Abstract

Limonene from citrus peel oil is valued as fragrance and flavor additives in food and beverages; however, D-limonene is highly volatile and oxygen-sensitive, thus present storage and stability challenges in food products. A novel, industrially-scalable microencapsulation by in situ complex coacervation during spray drying process (CoCo process) was applied to encapsulate limonene in alginate-gelatin matrix microparticles. Specifically, we investigated the potential to improve upon prior work demonstrating volatile retention and enteric release of limonene from the complex coacervated (CoCo) microcapsules by incorporating ethylcellulose to improve moisture and oxygen barrier properties of the encapsulation matrix. We hypothesized that ethylcellulose, commonly used as a water-barrier coating with pharmaceuticals, would enhance the ability of CoCo microcapsules to retain and shelf-stabilize limonene. The CoCo process alone could achieve limonene retention of 77.7% ± 1.3% during spray drying, with only ∼10% limonene loss and low oxidation rate after 3-weeks of storage in ambient conditions. Contrary to expectations, incorporating ethylcellulose with the CoCo formulation increased volatile losses of limonene during spray drying and during prolonged storage. Moreover, CoCo powders with ethylcellulose accelerated limonene release in water and simulated gastric fluid, and decelerated release in simulated intestinal fluid—a result that was contrary to targeting enteric release. Instead of simply forming a protective water barrier film in the microparticles during spray drying as envisioned, ethylcellulose appeared to bring limonene to the particle surfaces, thereby enhancing volatile losses, facilitating oxidation and accelerating release in acidic aqueous media. Using ethylcellulose as a model, this study demonstrated the potential to formulate CoCo microparticles using latex excipients to control burst release of the payload followed by long-lasting sustained release in air and in aqueous environments.

Surfactant-Free d-Limonene Encapsulation in Spray-Dried Alginate Microcapsules Cross-Linked by In Situ Internal Gelation

“…The particle size distributions of CLAM powders overlaid each other, and the observations from the electron micrographs corroborated the size distributions from static light-scattering size measurements (Figure a). The particle size range and external morphology of d -limonene-loaded CLAMs were consistent with those of CLAMs spray dried with nonvolatile food oils , and d -limonene-loaded complex coarcervated particles prepared by spray drying. ,, …”

“…The quantity of d -limonene near or at the surface of the spray-dried particles can be an indicator of the extent of volatile losses during spray drying . Minimal d -limonene was extractable from the surfaces of d -limonene-loaded CLAMs, and formulation had no effect on this “surface oil” (Table ).…”

“…The particle size range and external morphology of D-limonene-loaded CLAMs were consistent with those of CLAMs spray dried with nonvolatile food oils 19,20 and D-limonene-loaded complex coarcervated particles prepared by spray drying. 6,7,28 Cross sections of SF1-CLAMs and SF2-CLAMs revealed relatively large central cavities of several microns (Figure 3d and e). The size of these cavities, in agreement with the particle size distributions of the emulsions used to prepare the surfactant-free CLAMs (Figure 4b), suggests that the surfactant-free D-limonene CLAM process formed microcapsules with core−shell morphologies (Figure 3d and e).…”

“…30 The quantity of D-limonene near or at the surface of the spray-dried particles can be an indicator of the extent of volatile losses during spray drying. 28 Minimal D-limonene was extractable from the surfaces of D-limonene-loaded CLAMs, and formulation had no effect on this "surface oil" (Table 2). Previously, CLAMs loaded with nonvolatile oil exhibited considerably greater extractable surface oil, and the particle surfaces featured noticeable submicron-sized craters (matching the size of the nonvolatile oil emulsion droplets, which vaporize in the high vacuum SEM environment), the prevalence of which was correlated to the surface oil content.…”