Antifungal Activities Of Free Form Aroma And Glycosidic Aroma Precursors Against Tea Leaf Fungi

Glycosides are certain molecules in which a sugar part bound to some other part through its anomeric carbon to another group.Glycosides play important role in living organisms, many plants store important chemicals in the form of inactive glycosides for its stability. Not only much monoterpene alcohols and aryl alcohols in tea leaf,but also significant amount of glycosidically bound form volatiles are accumulated in the leaves of Camellia sinensis(L.) O.Kuntze with monoterpene alcohols and aryl alcohols as the major aglycones,these aglycones will be released from their respective glycosides by endogenous enzymatic hydrolysis under the conditions of leaf plucking,tissue damage, pest damage and malady infection etc.,the released volatiles aglycones are the basic part of tea aroma.A crude glycosides was extracted from fresh tea leaves and treated with the crude tea enzyme,cis-3-hexenol,linalool oxides,linalool,methyl salicylate,geraniol,benzyl alcohol and phenylethanol were monitored to be the major aglycone moieties by gas chromatography analysis.Quantitative and qualititative analysis showed that the amounts of the aglycone moieties of glycosides were higher than relative compounds in free form.Both the glycosidic aroma precursors and free form tea aroma components exhibited inhibitive activities against tea leaf pathogenic fungi(Phyllosticta theicola petch, Pestalozzia theae Sawada,Gloeosporium theae-sinensis Miyak,Colletotrichum Camelliae Massee)obviously in vitro.Glycosidic aroma precusors exhibited inhibitive activities during concentration between 5.0 mg/mL to 25.0 mg/mL in Potato Dextrose Agar(PDA) culture medium,free tea aroma components exhibited different inhibitive activities during the concentration between 100μg/mL to 2000μg/mL in PDA culture medium,geraniol shown the strongest inhibitive activity in seven volatiles.Tea polyphenols were widely believed as substance possess wide range of antibacterial while was evaluated no inhibitive activity against choosed fungi,it shown no inhibitive activities as well as EGCG(ep igallo-catechin gailate) even up to the highest concentration 80 mg/mL in PDA medium.Among the three kinds of major tea leaf components,the free form tea aroma and glycosides aroma precursor componets revealed positive correlation with tea leaf pathogenic fungi resistance.The activity ofβ-glucosidase was detected in liquid culture medium of pathogenic fungi, and the glycosidic aroma precursors was hydrolyzed by the germinated enzymes,in vitro antifungal test of glycosides,it proved that the antifungal effect is due to the release of the aglycone to achieve.Therefore,it was deduced that the free aroma are formed and stored as glycosides in the intact tissue of tea leaf and hydrolyzed by the actions of both the endogenous and exogenous glucosidase to release volatiles as antifungal substances when exposed to fungi infection.The effect of free aroma on tea disease defense system and tea aroma,which provides a valuable tool for screening potential tea plant cultivar with higher aromatic quality and tea leaf diseases-resistance.