How oregano essential oil can be transformed into a taste-masking controlled release solid formulation

Oregano essential oil (OEO) has antioxidant, antiproliferative, anti-inflammatory and antimicrobial activities. OEO could be administered orally for some gastrointestinal diseases, however, its oral use, is severely hampered by its irritant taste, which requires a high dilution in water before administration, and by its high susceptibility to light and humidity. Moreover, phenols have a high instability during digestion, and are rapidly metabolized, so that only a small fraction of the oral dose reaches the lower gut. Protection of OEO from degradation in the gastrointestinal tract is essential for its enhanced efficacy and sustained release.


  • Encapsulation of the oil in a solid form enhances its physical and chemical stability.
  • Tablets containing oregano essential oil were prepared.
  • Coated tablets protect phenols during digestion.
  • Tablets are less expensive than capsules and have a better stability.
  • The coating protects the oil from instability and volatilization.

The aim of this work has been the preparation and characterization of tablets based on hydroxypropyl methylcellulose (HPMC) granules containing OEO adsorbed on zeolite and coated with Eudragit® E PO to protect the oil from instability. Measurements of angle of repose demonstrated that OEO-containing zeolite granules were not cohesive and could be easily compressed.

The obtained coated tablets had sufficient mechanical strength and were able to prevent the oxidation of polyphenols in the stomach, indeed only the 15 and 30 % of them was released in simulated jejunal and ileal fluid, respectively. These solid dosage forms protect phenols contained in OEO from degradation and volatilization, as suggested by TG analysis.

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Folin-Ciocalteau reagent, gallic acid, carvacrol, hydroxypropyl methylcellulose (HPMC) as well as all the inorganic salts and reagents were purchased from Sigma (Milan, Italy) and used as received. Oregano essential oil (OEO) was provided by Alidans S.R.L. Zeolite (clinoptilolite, average diameter <50 μm) was provided by Zeocel Italia (Pisa, Italy). Eudragit® E PO was donated by Evonik Nutrition & Care GmbH (Darmstadt, Germany). Caco-2 cell line was purchased from the American Type Culture Collection LGC standards (ATCC HTB-37, Milan, Italy) and propagated as indicated by the supplier. Complete Dulbecco’s Modified Eagle medium (DMEM), fetal bovine serum (FBS), glutamine, penicillin and streptomycin were purchased from Sigma (Milan, Italy). Cell proliferation reagent (WST-1) was provided by Roche diagnostic (Milan, Italy).

Chiara Migone, Anna Maria Piras, Ylenia Zambito, Celia Duce, Elena Pulidori, Lorenzo Guazzelli, Andrea Mezzetta, Angela Fabiano, How oregano essential oil can be transformed into a taste-masking controlled release solid  formulation, LWT, Volume 201, 2024, 116281, ISSN 0023-6438,

Read also our introduction article on Orally Disintegrating Tablets (ODTs) here:

Orally Disintegrating Tablets (ODTs)
Orally Disintegrating Tablets (ODTs)
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