Study On The Chemical Basis Of Characteristic Flavor Of Pu-erh Raw Tea Made From Ancient Trees

Ancient tea tree is a kind of tea tree distributed in natural forests, including wild trees, half cultivated trees and cultivated trees which are more than 100 years old. This study selected 13 Pu-erh raw tea samples from Xishuangbanna and Lincang districts, tec. Then explored the chemical basis of the characteristic flavor of Pu-erh raw tea made from ancient trees from both chemical analysis and sensory evaluation.This study used ultraviolet (UV) spectrophotometry and high performance liquid chromatography (HPLC) to detect main taste components.Tthe result shows the average contents of taste components in tea samples made from ancient trees are:water extracts 51.53%, polyphenols 24.75%, catechins 14.96%, caffeine 4.27%, flavonoids 1.58%, free amino acids 3.85%, water-soluble sugar 3.81%. Compared with Pu-erh raw tea made from ground trees, the contents of the polyphenols, simple catechins, caffeine, free amino acids and total water-soluble sugar in samples made from ancient trees are significantly higher, while the contents of catechins, ester catechins, flavonoids are significantly lower.This study used two formula to evaluate the taste of pu-erh raw tea infusion: "(EGCG+ Flavonoids)/Total water extracts" is used to evaluate bitterness, "Free amino acids + Water-soluble sugar)/(EGCG+ Flavonoids)" is used to evaluate umami. The results of these two indices are highly in consistency with the results from sensory evaluation, which means using these two indices to evaluate the taste of pu-erh raw tea has applicability, accuracy and viability. The result shows the bitterness index of the 13 samples made from ancient trees is 0.102-0.155. The average is 0.127, which is 15% less than that of the samples made from ground trees. The umami index is 0.986-1.458. The average is 1.186, which is 19.80% higher than that of samples made from ground trees. These results indicate that in comparison with tea samples made from ground trees, those made from ancient trees have less bitterness taste, stronger umami taste and sweet aftertaste.Making use of SPME and GC-MS to extract, separate and identify the volatile aroma compounds of tea samples. Ninety-four aroma compounds are identified from samples made from ancient trees, most of which are alcohols (average contents 53.27%). In comparison with the control samples, the average content of Alcohols in the samples made from ancient trees is significantly lower (P<0.01), the average contents of Aldehydes is significantly higher(P<0.05). The common chemical basis of the aroma in two kinds of tea is linalool and its oxides. But the contents of them are different. In samples made from ancient trees, the average contents of linalool oxide,1-octen-3-ol, benzaldehyde, β-ionone, α-ionone and volatile higher fatty acids and their derivatives are significantly higher, while the linalool and (Z)-3-hexene caproate are significantly lower. These results indicate that the two kinds of tea vary on aroma basis and overall aroma characteristics. The aroma basis of samples made from ancient trees is the compounds present intense flowers, wood and camphor aroma. Other components while continuing to enhance its woody aroma, on the other hand making the overall aroma more pure, more coordinated, and last longer. The main aroma feature of samples made from ground trees is the components present fresh flower and wood aroma, coupled with other components which present fruity and refreshing aroma.The result of principal components analysis of the samples made from ancient trees shows the characteristic volatile aroma components in these samples are:linalool and its oxide, a-Ionone, β-ionone, geranyl Acetone, dihydroactindiolide, (E)-2-hexenyl hexanoate, (Z)-2-decenal, β-cyclocitral, 1-octen-3-ol, cis-jasmone, (Z)-3-hexenyl hexanoate, hexanoic acid-ethyl ester, nerolidol, geraniol, nonanal, methyl salicylate. A pu-erh raw tea aroma quality evaluation is built up based on principal component analysis:F=0.0364x1-0.0682x2-0.0190x3+0.0302x4......+0.0317x52+0.0216x53. As it is basically in consistency with sensory evaluation, it is applicable and feasible for future evaluation.Using sensory evaluation and the dissolution amount and rate of polyphenols and amino acids to evaluate the steeping tolerance of the pu-erh raw tea made from ancient trees. The result shows that in comparison with pu-erh raw tea made from ground trees, the steeping rate of polyphenols and free amino acids of samples made from ancient trees is lower, which means their steeping tolerance is better. In addition, the coordination of bitterness and umami taste is better. In summary, the steeping laws of taste components of two kinds of tea samples are different, the samples made from ancient trees can be steeped 1-2 times more than those made from ground trees.