Metabolomics Analyses Of Aroma And Flavor Quality Of Tieguanyin

Tieguanyin,a premium variety of oolong tea,is a very important economic crop in Fujian Province.Complicated manufacturing process along with seasonal variations caused wide variations in the quality of commercial tea products.However,clear criteria for quality distinctions are lacking in the tea industry except for sensory evaluations.As a result,this study aims to take advantage of the power of metabolomics to uncover key components affecting the aroma and flavor quality traits of Tieguanyin.Results from this study may better understand factors fundamental to tea quality at the metabolite level and help to improve the manufacturing process.It also provides theoretical basis for establishing the criteria for tea quality distinction.Experimental details are outlined below:1.Comparative studies of aroma and flavor related metabolites of lightly baked and moderately baked TieguanyinA large set of lightly baked Tieguanyin(LT)samples were collected from major tea-producing regions in Fujian Province.Sensory evaluations were performed to remove outliers and in the end 96 tea samples were retained.To minimize differences generated from variations in the matufacturing process for making moderately baked Tieguanyin(MT),we decided to take an aliquot of collected commercial LT samples and transformed them to MT using the same method.The optimal baking condition for MT samples was investigated and baking at 120? for 2 h followed by baking at 110? for 8 h was found to yield a satisfactory result.The aroma and flavor quality of LT and MT samples were compared by metabolomics approaches compbined with sensory evaluations.Based on results from HS-SPME-GC-TOF-MS analysis,furanone,furfural,2-acetylfuran and 2-acetylpyrroleonly occurred in MT.Besides,the content of hotrienol was 4.7 times that of LT.Some alkans were more abundant in MT,for example hexadecane and undecane.In contrast,the contents of indole,nerolidol and jasmine lactone were 4.1,3.6 and 3.4 fold in LT compared to MT.Theanine,catechins and caffeine in tea samples were quantitated by UPLC-QqQ-MS analyses.The results showed that concentrations of C,GC and GCG were higher in MT whereas catechins in the epi-form,namely,EC,EGC,EGCG and ECG)were found to be present in higher amounts in LT.In addition,caffeine and theanine occurred higher in LT than in MT.Non-targeted analysis of methanol extracts of LT and MT samples were conducted by UPLC-Q-TOF-MS.In total,75 compounds were identified,including catechins,proanthocyanidins,flavonoids and their glycosides,organic acids,alkaloids and so on.According to the untargeted analysis,theanine,glutathione and theasinenensin B were higher in LT while GC,quinic acid and gallic acid were higher in MT.2.Comparative studies of aroma and flavor related metabolitesTieguanyin tea samples in different gradesDifferent grades of Tieguanyin samples were collected from two tea companies.Aroma profiles were studied by HS-SPME-GC-TOF-MS and chemometric analysis.The results showed that the level of jasmine lactone was positively correlated with the grade of LT.However,in MT samples,positive correlation was not observed.Again,UPLC-QqQ-MS analysis was utilized was used to measure the concentrations of catechins,amino acids and caffeine.The results showed that level of majority amino acids was positively correlated with the grade of MT,the level of majority cat catechins was negatively correlated with the grade of MT.Compared the total contents of catechins and amino acids of LT in different grades,the ratios of them were positively correlated with the grade of LT.3.Comparative studies the aroma and flavor related metabolites of Tieguanyin harvested in different seasonsTea samples were collected from the same area in spring and autumn in 2016.The contents of jasmine lactone,hotrienol and tridacane in Tieguanyin tea samples harvested in spring were found to be 95.76%,381.35%,and 25.59%higher than those harvested in autumn.The content of benzadehyde in autumn tea was higher 65.49%than spring tea,and the content of 2-butyl acrylate was 17.5 times that of spring tea.The contents of GCG,EC,EGC,EGCG and ECG were 14.95%,24.11%,15.09%,6.66%and 9.45%higher,respectively,than autumn tea.On the contrary,the content of GC and caffeine in autumn tea were higher than those in the spring tea samples.In summary,we have shown that quality analyses by metabolomics and by sensory evaluations yielded consistent results.Furan,pyran,pyridine and alkanes are unique aromas exclusively found inMT.Levels of theanine and GC within tea samples could help to distinguish MT from LT.Besides,comparing the ratio of catechins(C,GC and GCG)to those of catechin stereoisomers in their epi-form(EC,EGC,EGCG and ECG)could enable dinstinction between LT and MT samples.Aroma metabolites are more related to distinguish LT in different grades.In constrast,for quality distinction in MT,many amino acids have a positive role;whereas catechins usually have counteractive effects.The taste of spring tieguanyin is better than autumn.