Modified cyclodextrin type and dehydration methods exert a significant effect on the antimicrobial activity of...

The antimicrobial activity of essential oils and their constituents has led to increasing interest in using them as natural preservative agents. However, their high sensitivity to light and oxygen, their volatility and their low aqueous solubility are all obstacles to their application in the food, cosmetic or pharmaceutical industries. Encapsulation in cyclodextrins (CDs) is a solution for the application of such essential oils.

The complexation of carvacrol and thymol with hydroxypropyl (HP)-α-, HP-β- and HP-γ-CD, the behavior of the solid complexes prepared by freeze-drying and spray-drying methods and the antibacterial activity of solid complexes were studied. K_c values of HP-α- and HP-γ-CD complexes with carvacrol (118.4 and 365.7 L mol^-1 ) and thymol (112.5 and 239.7 L mol ^-1 ) were far lower than those observed for HP-β-CD complexes with carvacrol (2268.2 L mol ^-1 ) and thymol (881.6 L mol ^-1 ). The lower stability of HP-α- and HP-γ-CD complexes increased the release of compounds, thereby affecting the antimicrobial activity of carvacrol and thymol to a lesser extent than complexation with HP-β-CD, normally used in the encapsulation of carvacrol and thymol. HP-β-CD encapsulation of carvacrol and thymol markedly reduced their antimicrobial activity. The freeze-drying method barely affected the antimicrobial activity of carvacrol and thymol after encapsulation, while spray drying could be considered for the production of solid complexes in combination with the appropriate CD.

It was thus demonstrated that HP-α- and HP-γ-CD are very suitable alternatives for the encapsulation of carvacrol and thymol with the purpose of preserving their bacteriostatic and bactericidal activities. © 2020 Society of Chemical Industry.