Study On Key Quality Chemical Components Of Citrus-white Tea

In recent years,the cross-border combination utilization of tea and natural flowers,plants and fruits has developed rapidly,and the new blended tea created have more diversified flavor and quality characteristics.Among them,tea blended with citrus has become the most consumed blended tea in the world due to its characteristic flavors of both tea and citrus.‘Chazhigan’(Citrus reticulata Blanco ’Chachiensis’)is an authentic citrus variety for the production of traditional Chinese medicine ‘Guangchenpi’,which has a strong aroma and a mellow taste.In Guangdong and Fujian regions of China,‘Chazhigan’and white tea are usually blended to create citrus-white tea(CWs).Compared with white tea,CWs has a unique aroma and fresh,mellow taste.At present,there is no systematic report on the chemical substance basis of the characteristic flavor quality of CWs and its quality formation mechanism.In this study,sensomics combined with metabolomics methods were used to comprehensively characterize the basis of key quality chemicals in CWs.Then,the flavor quality and its formation mechanism of two different manufacturing methods were analyzed.Subsequently,the enzymatic and non-enzymatic simulated reactions revelated the mechanism of significant of polymethoxyflavones(PMFs)in CWs.In addition,human basophils were used to construct a human-derived cellular allergic model to explore the synergistic anti-allergic activity and mechanism of various PMFs in CWs.This systematical study analyzed the chemical basis of flavor quality and its antiallergic effect of CWs,and provided a theoretical basis for expanding the research on the cross-border comprehensive utilization of tea and flowers,plants and fruits.The main results are as follows:1.The volatile and non-volatile components of raw materials(white tea,‘Chazhigan’)and CWs processed by two processing methods were analyzed by non-targeted metabolomics method based on Stir bar sorptive extraction-Gas Chromatography-Mass Spectrometer(SBSE-GC-MS)and Ultra-high performance liquid chromatographyquadrupole-time-of-flight mass spectrometry(UHPLC-Q-TOF/MS).Compared with the raw materials,the volatile and non-volatile components of CWs have significant changes.The volatile components are mainly composed of aromatic hydrocarbons,alkenes,nitrogen-containing compounds,and alcohols,in which limonene(11.58-19.87%),and methyl 2-(methylamino)-benzoate(17.61-25.95%)accounted for a higher proportion.In non-volatile components significant increase in vitamin C and over 122 kinds of nonvolatile compounds were significantly different(p<0.05)among all samples.2.Through SBSE-Gas Chromatography-Olfactory/Mass Spectrometer(SBSE-GCO/MS)and SBSE-GC-MS methods,99 aroma components in CWs were identified,mainly woody,herbal,and floral odorant,which were consistent with the results of aroma sensory evaluation.Among them,22 key aroma components(Odor Activity Value,OAV>1.0),trans-β-ionone(138953)and limonene(72919)OAV were significantly higher than other key aroma components.PLS-DA model analysis obtained the key different aroma components,and the results showed that terpenoids were the main contributors to the characteristic flavor of CWs,especially cuminaldehyde,Cubebol,1-methyl-4-(1-methylvinyl)-2-cyclohexen-1-ol and trans-linalool oxide(furanoid).There are significant differences in the key aroma components of CWs made by different processing methods.The composition of the aroma components of treatment 1 is similar to that of WT,and melonal,teaspirane,cubebol,2,4-decadienal,cuminaldehyde were the different key aroma compounds in treatment 1;treatment 2 is similar to dried citrus peel(DCP),and translinalool oxide(furan type),1-methyl-4-(1-methylvinyl)-2-cyclohexen-1-ol and(Z)-3-hexenylbenzoate were the different key aroma compounds in it.3.Taste sensory evaluation and targeted metabolomic analysis of Ultra-high performance liquid chromatography-quadrupole orbitrap mass spectrometer(UPLC-QExactive/MS)showed that the content of theanine,kaempferol/quercetin/myricetin and its glycosides,proanthocyanidins and chlorogenic acid/neochlorogenic acid in white tea decreased,which is the main reason for the taste of CWs is sweet and mellow.There are 7key taste components(Dove over threshold,Dot >1.0)in CWs,including EGCG,ECG,EGC,kaempferol 3-O-rutinglycosides,quercetin 3-O-galactoside,quercetin 3-O-glucoside and caffeine.4.The mechanism of increasing the content of PMFs in CWs was analyzed by simulation experiments.The hesperidin(monomethyl),nobiletin(hexamethyl),and tangeretin(pentamethyl)in DCP interact with tea leaves,and promote the synthesis and accumulation of methyl catechin(EGCG-3’’-Me).Under the optimal reaction conditions with sufficient substrates,1 mg of EGCG-O-transferase catalyzed the synthesis of 0.27-0.30 mg of EGCG-3’’-Me using the above three kinds of PMFs as methyl donors,respectively.The average conversion rate EGCG was over 85%.This was the main reason for the increase of methyl catechin(EGCG-3’’-Me)in CWs.In addition,under high temperature conditions,EGCG could directly react with flavonoids in DCP to form a small amount of EGCG-3’’-Me.5.Human basophil KU812 was used to construct a cell allergy model,and it was confirmed that the dominant PMFs of CWs have significant anti-allergic ability.The results of flow cytometry showed that the PMFs in CWs could reduce the allergic reaction of cells by inhibiting the expression levels of CD63 and CD203 proteins on the surface of KU812 cells and inhibiting the release of histamine in cells.The inhibitory ability of hesperidin,nobiletin,and tangeretin in combination with EGCG and EGCG-3’’-Me on the expression of CD63,CD203 and histamine release was significantly lower than that of the single compound.