Effect Of Brewing Conditions And Characteristic Aroma Compounds On The Quality Of Keemun Black Tea

Keemun black tea is one of the top ten famous teas in China.Is known as the world’s top three high-fragrance black teas together with Darjeeling black tea and Ceylon black tea in India.It has a worldwide reputation for its unique aroma--"Keemun aroma",which is "flower-like,fruit-like and honey-like" and is widely loved by consumers around the world.The formation of the flavor of Keemun black tea is closely related to its place of origin(climate,soil,light,and water source),highly suitable tea varieties,and mature teamaking technology.Its quality consisted of color,taste,and aroma.In consumer’s daily drinks,the main factor that affects the quality of Keemun black tea is brewing conditions.Some scholars have explored the effects of brewing conditions on tea,but most of them focused on the content of functional components and antioxidant capacity.And most of them are based on single factor brewing conditions.Besides,many studies have shown that there is an interaction between smell and taste,which has broad development space in the promotion and application of a healthy diet.However,this interaction has not been used effectively in tea processing and production.This study took Keemun black tea as the research object,using the response surface method to design the experiment with different preparing conditions(temperature,time,water tea ratio,and particle size).Using high-performance liquid chromatography,gas chromatography-mass spectrometry to detected the effects of different brewing conditions on Keemun black tea brewing infusions(BTIs).Evaluated the flavor quality,through the quantitative description analysis(QDA)to explore the effects of brewing conditions on BTIs’ flavor.Through detection and analysis,the characteristic aroma substances in Keemun black tea(geraniol and β-ionone)were selected and added to BTIs,to explore the influence of adding characteristic aroma substances on the taste attributes of BTIs.The main research contents and results are as follows:1.49 kinds of non-volatile compounds in BTIs were determined by high performance liquid chromatography(HPLC)and other detection methods.Meanwhile,BTIs under different brewing conditions were evaluated by quantitative descriptive analysis.The content of TWSS(total water-soluble substances)under different brewing conditions increased with the increasing of brewing temperature and brewing time.The trend of the total soluble sugar,total phenolics,total flavonoids,and flavonoid glycosides,and theaflavins in BTIs under different brewing conditions were consistent with the trend of water extract.Some substances with different trends may be related to the mutual conversion,the stability of components under thermal conditions,and the rules of leaching.All the substances were positively correlated with the overall acceptance,indicated that taste attributes of the BTIs were comprehensively affected by the phytochemicals in BTIs.Each component has its specific contribution.Among which,the caffeine,epigallocatechin(EGC),citric acid,lysine(Lys),theanine,malic acid,gammaaminobutyric acid(GABA),valine(Val),isoleucine(Ile),tannins,vitexin-2’’-Orhamnoside(Vit-rha)affected the overall acceptance of the BTIs most.Pearson correlation analysis,principal component analysis(PCA),response surface analysis,and other analysis methods were used to analyze the effect of brewing conditions on the taste attributes of Keemun black tea.Among four factors,Particle size has the most significant effect on the content of non-volatile compounds and the taste attributes of BTIs.The appropriate intensity of bitterness,astringency,and sourness constitutes the mellow taste of BTIs,and easier to get higher overall acceptance.However,excessive or lack of these tastes may lead to an unduly intense or bland taste and lower acceptance.The optimized brewing conditions were obtained by response surface methodology,and the brewing conditions were as follows: 89.1℃(89.0℃),6.02 min(6.00 min),56.2 m L/g(55.0 m L/g),and 2000 μm.2.Volatile substances of BTIs were collected by headspace solid-phase microextraction and were qualitatively analyzed by gas chromatography-mass spectrometry(GC-MS).The brewing conditions could affect the composition and content of volatile compounds of BTIs.About 50 volatile compounds were detected in BTIs,mainly divided into alcohols,aldehydes,esters,terpenes and terpenoids,and ketones.The proportion of these volatile compounds were alcohol>aldehyde>esters>terpene hydrocarbon>ketones>others(hydrocarbons,phenols,and pyrazine).Through PCA analysis these volatile compounds had great contributions to BTIs’ aroma: methyl salicylate,benzaldehyde,linalool,geraniol,nerol,2,6,6-trimethyl-1,3-Cyclohexadiene-1-carboxaldehyde,β-ionone,(Z)-3-Hexenyl-α-methyl butyrate,hexanal,and benzene acetaldehyde.Among them,geraniol and β-ionone had the highest odor activity value(OAV).As the brewing temperature and brewing time increased,the proportion of alcohols increased gradually,while the proportion of aldehydes decreased slightly,and the effect of brewing time on the proportion was bigger than that of brewing temperature.With the increase of water/tea ratio,the proportion of aldehydes and esters increased gradually,while the proportion of alcohols decreased gradually,and the water/tea ratio was the most influential brewing condition for the composition of volatile compounds.However,the change of particle size had no significant effect on the composition of aroma compounds,while it affected the non-volatile compounds most.3.The exogenous characteristic aroma compounds(geraniol and β-ionone)were added to BTIs.When the two exogenous aroma compounds were added separately,the bitterness,sweetness,and sourness of the BTIs increased,while there was no obvious effect on the umami taste.The reasons for the increase in the scores of these three taste attributes were speculated as follows: the taste of aroma compounds themselves,the congruency between aroma attributes and taste attributes of these aroma compounds,which could be reduced to the interactions between odor and taste.When the two kinds of exogenous aroma compounds were mixed,the sweetness of tea soup decreased gradually when the concentration of geraniol was low and the concentration of β-ionone was increased.However,at a high geraniol concentration,the opposite trend was observed.