Preparation, characterization, and in vitro release of microencapsulated essential oil hydroxyapatite pellets filled into multifunctional capsules

Abstract

Oregano essential oil (EO)–loaded pellets were prepared using calcium phosphate substrates of different specific surface areas (Sw) and as binders EO in water emulsions with low or high EO content, stabilized with polysaccharides (PSC) or a combination of PSC-Eudragit® L100-55 (PSC-PLM) encapsulants. Tri-cafos® 250 with high Sw gave higher EO loading and more spherical pellets with narrow size distribution. These were filled into the following hard-shell capsules: gelatin, hydroxypropyl-methyl cellulose (HPMC) based immediate release (Vcaps® plus), gastro-resistant (DRcaps®) and enteric release (Vcaps® enteric), and pullulan (Plantcaps®). FTIR and Raman spectroscopy showed H-bonding between PSC and EO and between PSC and PLM. Pellet mechanical strength decreased with EO content and pellets made with PSC emulsions were stronger than PSC-PLM pellets proving PSC binder ability. Disintegration and release of EO from capsules filled with immediate release pellets (PSC) or enteric pellets (PSC-PLM) were tested sequentially in pH 1.2 and 6.8. Capsule shell influenced disintegration and release. The release of EO from the PSC pellets within 1 h, at pH 1.2 was from gelatin 82%/85% (for low/high EO emulsions) but from Vcaps® plus and Plantcaps® it was lower, 36%/38% and 45%/70% respectively. DRcaps® and Vcaps® enteric capsules confirmed gastro-resistance. The release of enteric (PCS-PLM) pellets was: from gelatin and Vcaps® plus capsules 21%/23% and 20%/21% respectively, but from Plantcaps® 61%/62%, indicating deactivation of Eudragit® L100-55 functionality in the last case. In all cases, release was complete after 180 min, but release of enteric pellets from Vcaps® plus was slower than from gelatin capsules due to the presence of HPMC.