Carvacrol-loaded montmorillonite–caseinate hybrids as active additives for the development of antimicrobial alginate-chitosan microcapsules

This study presented a novel approach for encapsulating carvacrol, a volatile compound with antimicrobial properties, using montmorillonite-based hybrid materials prepared via an evaporation–adsorption process under vacuum at room temperature. These hybrids were incorporated as active additives into alginate-chitosan microcapsules. The effect of montmorillonite surface functionalization was examined by preparing two types of carvacrol-loaded composites: one with sodium caseinate intercalated within the clay layers, and another with caseinate adsorbed onto the external surface. Among these, the intercalated composite (Cas0.5@Mt-3) showed the highest carvacrol adsorption capacity, reaching 176.87 mg/g compared to 155.83 mg/g for the unmodified clay. This enhancement was attributed to the diffusion of carvacrol into the interlayer space, as supported by XRD analysis showing increased interlayer spacing.

The carvacrol-loaded hybrids were incorporated into alginate matrices at three concentrations (1 %, 2 %, and 3 % w/w) using ionotropic gelation to form stable microcapsules. Higher encapsulation efficiency and loading capacity were achieved with the hybrid composites, likely due to the amphiphilic nature of caseinate, which improved compatibility between the additive and the polymeric matrix, as confirmed by FT-IR and TGA analysis.

In vitro release studies in food-simulating media revealed more controlled carvacrol release in aqueous medium, while acidic and oily conditions led to faster diffusion. Antimicrobial tests against selected strains demonstrated enhanced inhibition, attributed to the synergistic effect of carvacrol and the polymeric components, particularly chitosan used for crosslinking. These results supported the effectiveness of this approach and its potential for developing active polymer-based systems to improve carvacrol bioavailability in food-related applications.