Microencapsulation of essential oils from Origanum vulgare L. and Minthostachys mollis: Physicochemical properties and antimicrobial activity

The essential oils of Origanum vulgare L. (orégano) and Minthostachys mollis (Kunth Griseb) (muña) have been recognized for their antimicrobial and antioxidant properties; however, their direct application is limited by high volatility, low solubility in aqueous media, and sensitivity to environmental factors. The objective of this study was to characterize the essential oils of O. vulgare and M. mollis , microencapsulate them, and evaluate the antimicrobial effect of the microcapsules against the bacteria Escherichia coli and Staphylococcus aureus , as well as against the phytopathogenic fungus Botrytis cinerea . Using gas chromatography coupled with mass spectrometry (GC-MS), 53 volatile compounds were identified in O. vulgare oil and 56 in M. mollis oil, with oxygenated monoterpenes such as linalool, verbenone, and linalyl acetate predominating. Microcapsules made with M. mollis oil showed greater encapsulation efficiency (87 ± 2 %) and yield (19 ± 3 %) compared to those made with O. vulgare (72 ± 3 % and 16 ± 2 %). Both formulations exhibited high water solubility (>83 %), low water activity (<0.3), uniform spherical morphology, and adequate thermal stability, as determined by DSC, XRD, and TGA analyses. The essential oils in their free form exhibited high antioxidant capacity (59 ± 2 mg Trolox equivalents per gram). Free essential oils (OEO, MEO) exhibited lower MIC and MBC against S. aureus and E. coli compared to their microencapsulated counterparts (OM, MM), with significant differences (Duncan, p < 0.05). Nevertheless, due to the controlled release of active compounds, they maintained consistent antimicrobial action, producing inhibition zones greater than 2.5 cm. In addition, M. mollis microcapsules stood out for their greater stability in terms of water activity and improved optical properties, reinforcing their potential application in sustained-release systems and functional matrices with prolonged bioactive activity. • The essential oils were rich in phenolic compounds and oxygenated monoterpenes. • Microencapsulation with β-cyclodextrin improves stability and solubility. • Microcapsules maintain an antimicrobial effect against E. coli and S . aureus. • Both essential oils inhibited B. cinerea by 100 % at 100 mg/mL. • M. mollis showed greater encapsulation efficiency and Aw stability.