Detection Of Aroma Of Pu'er Raw Teas From Ancient Tea Trees And An Evaluation On Their Nectar Fragrance Constituents

Pu'er raw teas from ancient trees was a kind of famous tea with high value,whose aromatic type was regard as “nectar fragrance” based on sensory evaluation in tea industry.Up to date,little was executed on the qualitative and quantative analysis of characteristics aromatic constituents composed “nectar fragrance”,and even primary aromatic constituents of Pu'er raw tea from ancient trees.Further,Pu'er tea market is inundated with the counterfeits.The tender shoots of tea trees in the original plance of the ancient tea trees were plucked and processed into Pu'er raw tea,whose aroma constituents was detected and calculated by chemical metrology.The main research content and conclusions are as follows,which could be referred for formulating the processing standard for discriminating the fakes of Pu'er tea.(1)Gathering samples: Production places of twenty-one ancient tea tree,with the same habitat conditions and similiar tree vigor,were chosen from Pu'er tea region,Banna tea region,Lincang tea region and Pu'er tea group(located I Ning'er County)which belonged to Pu'er tea original production place in Yunnan province.The tea tree tender shoots were plucked and processed into Pu'er raw tea,according to the identical plucked standard and the same criterion,within 2 days before and after tomb-sweeping Day and the late September.The essential oils of the all samples were extracted,qualitatively and quantatively analyzed,in which the “nectar fragrance”chemical composition was discussed emphatically.(2)Preparation experiments: The partial parameters of the traditional simultaneous distillation extraction device(SDE)were modified as follows:the temperature measuring part of an industrial thermometer was embed within the glass tube of one side of SDE for real time monitoring the temperature of the mixture of tea,water and steam in the extraction process;then a glass fibre net was embed in the same tube to restrain the boiling degree of the steam;the extracting time reduced from 50 min to 20 min for avoiding potentially occurred chemical reaction to aromatic constituents;ether was chosen as solvent for promote the extract efficacy.The detecting results proved that the stability and efficacy of extraction of SDE Then,parameters were modified enhanced,which was used to extract the essential oils of the tested samples.(3)Pu'er tea fragrance ingredient determination: 322 aromatic constituents of Pu'er raw teas from the 21 production places were identified by mass chromatography coupled of mass spectrometer(GC-MS),according to comparison of mass spectra and retention times with those of authentic standards,and quantified by their relative abundance to the internal standard(decanoic acid ethyl ester).The aromatic constituents included alcohols,aldehydes,esters,ketones,hydrocarbons,heterocycles and acides.The statistic analysis revealed the composition and the contents of aromatic constituents of each of four tea regions were relatively consistent with another,which not only were different from those of Pu'er unripe tea,but also unlike those of green tea.(4)Pu'er raw tea,whose aroma constituents was detected and calculated :Twenty-six mutual constituents existed in the four tea regions were screened out and represented the primary aromatic type of Pu'er raw tea.From which twelve high content constituents were selected and occupied 80.0% of the content of 26 mutual constituents.Based on a principal component analysis on26 mutual constituents,six characteristics constituents were calculated out,which were exactly contained in high content constituents,called “nectar fragrance” constituents.They were D-limonene,trans-linalool oxide,linalool,?-terpineol,trans-?-ionone and cis-nerolidol,accounted for 75% of the content of 12 high content constituents.At the same time,an orthogonal partial least squares discriminant analysis(OPLS-DA)was used to parse the twenty-six mutual constituents,referring to criterion of VIP>1,and the same six characteristic constituents were predicted,i.e.“nectar fragrance”constituents.(5)Confirmation of aroma constituents: In order to verify the research results of the spring tea,a batch of Pu'er raw teas were also processed,according to the same tea shoots-plucked and manufactured criterions,within the 21 production places,during late September of autumn tea harvested stage.Two hundred ninety-eight aromatic constituents were identified from the batch of teas,which contained alcohols,aldehydes,esters,ketones,hydrocarbons,heterocycles and acides,too.26 mutual constituents,identical to those of spring tea,were chosen from the four tea regions,from which the same 12 high content constituents were also chosen.Based on PCA(Principal Component Analysis)and OPLS-DA,six “nectar fragrance” constituents the same as those of spring tea were forecasted from the 12 high constituents.(6)Results and analysis: Taken 21 mutual constituents as samples and each content as variables,eigenvectors and eigenvalues on the first seven principal components were calculated out by PCA.And the cumulative contribution rates on the first and the second principal components attained to ?96%.Therefore,the rank results on PCA coordinate system were authentic,and seven dimensions could be reduced to two dimensions.Made the first principal component and the second principal component as X axis and Y axis,to build PCA coordinate system,in which 26 mutual constituents form two distinct sections,of which six “nectar fragrance” constituents one section.The six “nectar fragrance” constituents were also calculated out of the 26 mutual constituents by means of OPLS-DA.The research results on sping teas were consistent with those on autumn teas.If take the 21 production places as samples,and each several checked out quantity as variables,the 21 production places could be accurately classified into four groups which originally derived from 4 tea regions,which proved the reliability of the used algorithm on the other hand.It was considered that the aromatic constituents of the Pu'er raw teas from ancient tea trees were comprehensively identified first,and six “nectar fragrance” constituents were worked out with the aid of PCA and OPLS-DA,all those could be refered for standardized production of Pu'er raw tea and the supervision of the fake.