Dynamic Changes Of Flavor Quality Of Jinhua White Tea During Processing

With the steady development of white tea industry,the existing product structure has been unable to meet the increasing diversified needs of consumers.Enriching the structure of white tea products,extending the industrial chain and improving the resource utilization rate of old white tea with coarse raw materials,the market share of many white tea derivatives such as Jinhua white tea has gradually expanded.In this study,Fujian Shoumei was selected as the raw material,and the processing technology of Hunan Fuzhuan tea was used for reference to make Jinhua white tea.The key stage samples in the processing process were taken as the research object to explore the formation of flavor quality of Jinhua white tea.The main results are as follows:(1)Sensory evaluation results show that the sensory quality changed obviously from Shoumei to fungal fermentation 8 days(S5),but little from S5 to the end of drying(S8).The technology of artificially controlling temperature and humidity to make white tea fungal fermentation is similar to the aging process of white tea to some extent.The difference is that the fungal fermentation process not only makes the new white tea have the taste of aged white tea,but also has the unique fungal flower aroma.The results of physical and chemical detection show that the relative contents of tea polyphenols,ester catechins,theaflavins,free amino acids,water extracts and soluble sugars decreased in different degrees by 27.79%,69.70%,52.56,24.91%,6.25% and 18.77% respectively.The content of all polyphenols decreased the most from fungal fermentation 4 days(S4)to S5.Only EGC content in catechins showed a fluctuating upward trend.Met changed the least during the whole processing,while Gly remained the lowest in all components.Except Glu and Gly,all other amino acid components showed an increasing trend during drying.The relative contents of flavonoids,theobromine and caffeine increased slightly before and after processing.The relative content of GA increased significantly,with an increase of 96.08%.(2)Nonvolatile substances were detected by metabonomics,269 kinds of non-volatile metabolites in 11 categories were identified qualitatively,and the total amount increased first and then decreased,with an overall decrease of 22.23%.From the S5 to S8,the content of all kinds of substances changed little.The content of flavonoids is always higher than other compounds.Amino acids and derivatives,organic acids and derivatives,flavonoids,terpenoids and glycosides,nucleosides/ nucleotides and analogues,coumarins and derivatives are the key compounds that affect the quality of Jinhua white tea.The relative contents of amino acids and derivatives,nucleosides/nucleotides and analogues,flavonoids,carbohydrates,terpenoids and glycosides,phenols,vitamins,organic acids and derivatives all showed a downward trend.Alkaloids content increased slightly(16.86%);The content of coumarins and derivatives and other substances increased significantly(p<0.05)with an increase of 504.42% and 99.76% respectively.These changes help to reduce the astringency of Shoumei raw materials,increase the sweetness and mellow degree,and enrich the fragrance type.The relative contents aromatic compounds homovanillicate,Shikimate,4-Feruloyl-1,5-quinolactone,2-(4-Hydroxyphenyl)ethanol,Methyl 10-gingerol obviously decrease from raw materials to fungal fermentation 0 days(S3)and S4 to S5.The relative content of jasmine lactone began to increase gradually after S3.It is speculated that these five substances are of great significance to the change of aroma quality of Jinhua white tea.(3)The results of PCA analysis of non-volatile metabolites in different stages showed that the processing of Jinhua white tea was divided into four stages,raw materials;pile fermentation;fungal fermentation 0 d to fungal fermentation 4 d;fungal fermentation 8 d to drying 8 d.A total of 162 differential metabolites were identified by OPLS-DA,amino acids and derivatives,flavonoids,terpenoids and glycosides,nucleosides/ nucleotides and analogues,alkaloid and carbohydrate are the key differential metabolite categories.Interestingly,except for the decrease range of key differential metabolites between S3 vs S4and S6 vs Drying 4 d(S7)which is higher than the increase range,the decrease range of relative content of key differential metabolites among other groups is significantly lower than the increase range,indicating that the change of taste quality of Jinhua white tea is mainly influenced by the up-regulation of differential metabolites.DL-Norvaline and Bicine mainly act on the change of taste at the early stage of flowering.S5 to S8 is the key period to form the quality of Jinhua white tea,Vitamins,phenols,coumarin and their derivatives have significant regulatory effects.Among them,Bergapten,Psoralen,L-dihydroorotate,Scopolamine,Homovanillicate were synthesized in large quantities at this stage,which was speculated to be closely related to the secondary metabolism of Eurotium cristatum.Kainic Acid,β-Homoproline,D-Quinovose,Pristimerin,Baccatin III mainly acts at the late flowering stage.Organic acids and amino acids such as DL-Homocystine,D-Arginine,Acetyl-DL-Leucine,5-Sulfosalicylic acid,L-α-Glutamyl-L-tyrosine,N2-Fructopyranosylarginine,1-Methylhistidine,Glutathione,Shikimate,Arachidic acid,Myristic acid,α-N-Acetyl-L-glutamine,4-Methylene-L-glutamine,(R)-3-Hydroxybutyric acid play an important role in the formation of the mellow quality of Jinhua white tea.Carbohydrates such as N-Acetyl-D-lactosamine,Ethyl glucuronide,4-O-β-Galactopyranosyl-D-mannopyranose,N,N’-Diacetylchitobiose,D-Arabitol,RUBUSOSIDE,Paclitaxel and Paclitaxel are helpful to change the taste of Sweet alcohol from green and astringency.The increase of alkaloid content was helpful to adjust the concentration of Jinhua White Tea.(4)Through HS/SPME-GC/MS detection of the volatile components of tea samples in different stages,195 volatile components were identified.Alcohols are the most important volatile substances in the whole processing process.Through principal component analysis combined with qualitative and characteristic analysis of various substances,Apricolin,Methyl salicylate,creamy lactone,1,5-Octalactone,Hexyl benzoate,(3Z)-3-Hexen-1-yl benzoate,(3Z)-3-Hexen-1-yl hexanoate,(Z)-linalool oxide(furanoid),β-ionone,à-Ionone,6-Methylhept-5-en-2-one,(-)-Cedrene,Decanoic acid,1-Hexanoic acid,Nonanoic acid,undecenal,Neral,trans-2-Hexenal,Isovaleraldehyde,beta-Homocyclocitral,Benzaldehyde,cis-3-Hexen-1-ol,(±)-trans-Nerolidol,1,6-Octadien-3-ol,3,7-dimethyl-,Nerol,1-Nonanol,Oct-1-en-3-ol and Succinimide,N-ethyl-are extremely important volatile components that affect the formation of the fungal flower aroma of Shoumei from white tea flavor.