Antifungal activities of major tea leaf volatile constituents toward Colletorichum camelliae Massea.

A crude glycosidic fraction was prepared from fresh tea leaves and treated with the crude tea enzyme, fractions of cis-3-hexenol, linalool oxide I (cis-furanoid), linalool oxide II (trans-furanoid), linalool, methyl salicylate, geraniol, benzyl alcohol, and 2-phenylethanol were monitored to be the major aglycone moieties by analyzing the released volatiles. The amount of the released aglycone moieties is 5.8 times higher than those in free form. For investigation of the functions of the glycosidically bound form aroma constituents in tea leaves, their antifungal activities were determined by antifungal assay. Geraniol, linalool, methyl salicylate, benzyl alcohol, and 2-phenylethanol exhibited significant antifungal activities toward Colletorichum camelliae Massea, although cis-3-hexenol and linalool oxides showed weaker activities by comparison. Among them, geraniol was shown to be the most potential antifungal substance with a MIC value of 440 microg/mL. The crude glycosidic fraction prepared from tea leaves also exhibited significant antifungal activities in a wide range of concentrations from 2 to 25 mg/mL in a PDA medium. It was deduced that the glycosidically bound volatiles are formed and stored in the intact tissue of tea leaf and hydrolyzed by the actions of both the endogenous and the exogenous glycosidases to release volatiles as antifungal substances when exposed to Colletorichum camelliae Massea. The results suggested that the higher content of the bound form geraniol in tea leaves of var. sinensis might be responsible for their stronger antipathogen properties toward tea leaf blight, as opposed to those of var. assamica.