Study on Formation Mechanism of White Tea Characteristics Based on Metabolomics and Proteomics Analysis

Author:Chen Qin Cao

Supervisor:lin zhi ni de jiang


Degree Year:2019





White tea,one of six kinds of teas in China,possesses umami and slightly sweet taste as well as fresh and high-pekoe odor.White teas subject to the simplest processing procedure,including only prolonged withering and drying.Present studies mainly focused on investigations to taste,aroma compounds and health benefits of white teas,whereas ignored the formation of and dynamic changes in those quality compounds during white tea processing,especially the prolonged withering period.This paper systematically studied the formation mechanism of white tea characteristics by combination analysis of multiomics.The main results are as follows:1 UPLC-LTQ-Orbitrap/MS was employed to investigate the changes in non-volatile components during white tea processing.97 non-volatile components were identified,including 2 alkaloids,17 amino acids,14 catechins,13 dimeric catechins,27 flavone and flavonol glycosides,5 glycosidically bound volatiles(GBVs),11 phenolic acids,6 nucleosides and nucleotides,and 2 other compounds.During the withering period,the content of caffeine increased,theobromine decreased;the content of most amino acids increased,while theanine decreased;the content of catechins,procyanidins,polyester catechins and phenolic acids decreased,and theaflavins increased;the content of flavone and flavonol glycosides showed irregular changes;the content of most nucleosides and nucleotides increased;the content of GBVs decreased.After drying,the content of alkaloids,amino acids,catechins,and part of flavone and flavonol glycosides significantly decreased;while the content of most dimeric catechins,part of flavone and flavonol glycosides,GBVs,nucleosides and nucleotides,and theanine glucosides significantly increased.2 GC×GC-TOFMS was employed to investigate the changes in volatile components during white tea processing.172 volatile components were identified and mainly comprised of endogenous biosynthesis volatiles,including fatty acid derived volatiles(FADVs),amino acid derived volatiles(AADVs),volatile terpenoids(VTs),and carotenoid derived volatiles(CDVs).During the withering period,the content of most non-ester FADVs increased,while ester FADVs increased firstly and then decreased,or increased at late stage;the content of most AADVs increased at the middle and late stages;VTs showed diverse change trends,the content of alcohols of monoterpenoid and alkenes of sesquiterpenoid increased,while alkenes of monoterpenoid decreased or remained stable.After drying,the content of most alkenes,most alcohols,a portion of esters,and several other compounds significantly decreased,while the content of aldehydes,most ketones and several esters significantly increased.3 Label-free proteomics and qPCR technology were employed to investigate the changes in key genes related to taste and aroma components during the withering period.Most proteins involved in amino acid and protein biosynthesis were down-regulated,while most proteins involved in protein hydrolysis were up-regulated,indicating that protein hydrolysis is the main factor promoting the increase in content of free amino acids.Most proteins involved in flavonoid biosynthesis were down-regulated,indicating that,in addition to being oxidized,the weakening of biosynthesis also accounts for decline in content of flavonoids such as catechins.Most proteins involved in metabolism of starch and sucrose were up-regulated,suggesting that insoluble polysaccharides may degrade into soluble sugars.The expression of most genes involved in biosynthesis of endogenous volatiles were consistent with the changes in corresponding aroma components,indicating that the differential expression of these key genes was responsible for the various accumulation of endogenous biosynthesis volatiles.4 The changes in 22 free amino acids and 10 GBVs during withering were absolutely determined.The content of four aroma precursors amino acids(phenylalanine,valine,leucine,isoleucine)increased at the early and middle stage then decreased slightly,and the content of GBVs showed decrease trends.At the same time,the content of AADVs increased dramatically at the late stage,and GBVs-corresponding aroma components increased greatly,indicating that increase of free amino acids and degradation of GBVs promote the formation of white tea aroma.5 Changes in most quality components of white tea mainly occurred in the prolonged withering period rather than drying,proving that the prolonged withering period is the key step for formation of white tea characteristic.After drying,the variation of non-volatile components was relatively little,while the variation of volatile components was relatively large,indicating that the drying is also an important step to promote formation of white tea aroma.