In vitro effect of thymol, carvacrol and linalool oils encapsulated in beta-cyclodextrins against Geotrichum citri-aurantii

Geotrichum citri-aurantii is one of the most important phytopathogenic fungi causing postharvest disease of citrus fruit. The conventional treatments for disease control are being restricted within the European food safety framework and therefore, it is necessary to seek for alternatives. In this work, the effect of the inclusion of two phenolic isomers (thymol, carvacrol) and a terpene (linalool) in (2-hydroxypropyl)-beta-cyclodextrins (HP-beta-CDs), carried out by two methods, solubility (DF) and microwave irradiation (S), on G. citri-aurantii growth was evaluated. DF complexes of thymol and carvacrol greatly inhibited the fungal growth in ELISA plates. In addition, these encapsulated oils at different concentrations (0, 2.5, 5, 12, 25 and 50 mM) and incubated during 0, 24 or 48 h at 24 degrees C in liquid potato-dextrose media had an inhibitory effect against G. citri-aurantii. At a concentration higher than 5 mM of carvacrol, DF complexes completely inhibited fungal growth. Culture media with linalool showed low effectiveness against G. citri-aurantii in both experiments. Encapsulation allowed the liberation of volatiles to maintain the antifungal and inhibitory activity of thymol and carvacrol for a longer period of time when compared with non-encapsulated oils. In this sense, it was observed that the use of the complexes obtained by the DF method could gradually regulate their antifungal and inhibitory action avoiding physiological damages and organoleptic changes in citrus fruits. The encapsulated oils could be a good alternative to the use of pure essentials oils and chemical fungicides.