Controlled release of antifungal volatiles of thyme essential oil from β-cyclodextrin capsules

Thyme essential oil (TO) is a good antimicrobial agent, however, its high volatility and reactivity limits its application as food preservative. beta-cyclodextrin (beta-CD) is able to encapsulate organic molecules, forming host-guest complexes with hydrophobic and volatile molecules such as TO constituents, controlling volatility and reactivity. In addition, controlled released of the beta-CD trapped compounds could be possible by exposing the capsules to high relative humidity (RH). With this in mind, the controlled release of antifungal volatiles throughout exposure of TO:beta-CD capsules to high relative humidity was studied. Thymol (TOL) was the major constituent of TO, detected by gas chromatography before and after encapsulation. Capsules of the 8:92 ratio (TO:beta-CD) showed the highest TOL content. Hydrogen bonds and hydrophobic interactions were detected between the oil constituent and beta-CD by IR and H-1 NMR spectroscopy. During moisture sorption, the TO capsules showed a lower water uptake compared with free beta-CD. Similar behavior was observed during water desorption. In all cases, a hysteresis process was observed when comparing sorption and desorption isotherms. At high RH, TOL is displaced and almost 76% is released to the headspace. The growth of Alternaria alternata was inhibited significantly by the addition and exposure to TO:beta-CD as measured by both the agar dilution and the headspace method, respectively. Therefore, the encapsulation of antifungal volatile compounds as TO in beta-CD, could be an alternative to control the release of natural antimicrobials that can be of interest to the agricultural area.