Research On The Material Basis And Quantitative Evaluation Of The Favor Quality Of White Tea

In recent years,white tea has developed rapidly,and it has been more and more popular in China because of its fresh flavor and good health care function such as anti-oxidant,anti-inflammatory,anti-cancer and so on.This experiment studied the differences in aroma and taste components among different kinds of white teas,including different grades,compressed and aged white teas.At the same time,in order to improve the quality evaluation method of white tea,the white tea aroma was divided into A(refreshing and delicate aroma),B(floral and fruity aroma),C(woody and aged aroma)three aroma types to quantitatively evaluate white tea samples.After comparing the differences in aroma quality of different kinds of white teas,correlation analysis,principal component analysis and multiple linear regression analysis were used to screen the chemical components related to each aroma type,and evaluation models were established.The same quantitative evaluations of the umami,bitterness and astringency of white teas were carried out,and the corresponding evaluation models were established.The main results are as follows:(1)The main aroma compounds measured by gas chromatography-mass spectrometry(GC/MS)in new white teas were linalool and its oxides,phenylethyl alcohol,benzaldehyde and so on.The aroma compounds in different kinds of white teas were analyzed by partial least squares discrimination(PLS-DA),and the result showed that there are significant differences.White Silver Needles and White Mudan contain higher linalool and its oxides,phenylethyl alcohol.For Shoumei,the contents of dihydroactinidiolide,methyl salicylate and other ingredients are high.What's more,the aroma composition of aged white teas is different from that of new white teas,and its main aroma compounds are a-cedrene,?-cedrene,cedrol and the like.And the aroma variety and content in compressed aged white teas are also obviously different from that in loose aged white teas.The content of linalool and its oxide in loose teas is higher than that in compressed teas.In compressed teas,the contents of terpene compounds such as cedrene and caryophyllene are high.(2)For aroma quantitation,the results showed that in new white teas,the aroma appearance were mainly composed of refreshing and delicate aroma as well as floral and fruity aroma.White Sliver Needle has the highest score of A aroma,while White Mudan is B aroma,and Shoumei is C aroma.Aged white teas were mainly composed of woody and aged aroma as well as floral and fruity aroma.The changes of score in White Sliver Needle were not obvious after the compressed processing.Meanwhile,the C aroma score of White Mudan and the A,B aroma scores of Shoumei were increased after the compressed processing.The effective evaluation models for A aroma and C aroma were established:A=0.67F1-0.68F2+0.57F3+4.02,R2=O.677;C=0.13F1-0.52F2+0.07F3-0.18F4,R2=0.711.(3)The determination of biochemical components in white tea samples showed that the total amount of tea polyphenols was generally lower than 20%,and the average amino acid amount was 5%.With the reduction of white tea level,the contents of tea polyphenols,EGCG,ECG,CG,GA were reduced,while the flavonoid content increased.Amino acid and caffeine contents were similar in White Sil-ver Needle and White Mudan,but significantly higher than that of Shoumei.Compared with the new white teas,the biochemical components of aged white teas were generally decreased,and the total-amount of amino acids,soluble sugar,tea polyphenols,EGCG,ECG and GA of white teas after compressed processing were further reduced.(4)For quantitative evaluation of the taste,the results showed that White Silver Needle got high score in umami,and White Mudan scored high in umami,astringency and bitterness at the same time,while Shoumei scored the lowest in all three tastes.The umami and astringency scores of aged white teas were lower than that of new white teas,and the umami score of the compressed aged teas further declined.The effective evaluation models for different tastes were established,Umami:U=-0.41F1?0.28F2+0.12F3,R2=0.850;Astringency:A=0.29F1-0.25F2-0.66F3,R2=0.650;Bitterness:B =0.11B1+0.19B2-0.39B3+0.39,R2=0.650.