| Oolong tea is a special type of tea differentiating with other types by its fruit smell and characteristic fragrance. Its high content of aroma oil content similar with that of flowers attracts experts' notions from domestic and abroad. So far, 162 kinds of components extracted from Oolong Tea were examined and among which Alcohols, Ketones, Esters, Aldehydes and Hydrocarbons were the main compositions. The essential compounds were estimated to come from three ways. One was the ready ingredients of fresh leaves. One was the outcomes of enzymatic reaction during the Zuoqing period. The third one was the outcomes formed by heating reations during the period of firng.The aroma of tea is the critical factor reflecting its quality and also is the important object in the study on quality of Oolong tea. It is certainly the key standard judging the quality of Oolong tea. With the advancement of trace analysis techniques, a large of studies were conducted on the composition of volatile compounds and the mechanisms of its formation of smell-related chemicals and many reports were reported.This research selected fresh leaves of Qingxin Oolong variaty as the raw material to process Oolong tea. During the procedure the dhools were sampled and dried for conservation and volatile essential oil was extracted by super critical. CO2.Then composition and relative contents were detected by CG/MS qualitatively and quantitatively, Meanwhile, The extracting techniques of Steam-distilling extract (SDE) and super critical CO2 extract (SC-CO2) were also compared1. To keep the volatile essential and primary color of Oolong, freeze-drying is used to dry the dhool sample . At first the sample was freezed at -45℃ for 300min, then vacuumized at -5℃ for 600min and at -10℃ for 900min separately. The extracted aroma essential of freeze-dried samples were almost the same as the non-dried dhool .It show that the colore and quality were keeped well and no chemical reactions were took place.2. To compare the extracting effects, SDE and SC-CO2 methods were used to extract, two Oolong finished products(one is rolled by hand rolling ,one is machine rolling),and the conditions of SC-CO2 were temperature 30 ℃, working pressure 30Mpa. It is found that the essential oil of tea leaf by SC-CO2 extraction has far much less β -ionone , nerolidol, α-farnesene than that of SDE method. It means SC-CO2 extraction, method can authentically reflect the odorous constituent of tea-leaf.3. SC-CO2 is used in Oolong making process: from fresh leaf, sun withering, Zuoqing 1, Zuoqing 2, Zuoqing 3, to drying products. Results showed vinyl is the least content of Oolong tea, cool green leaf has a peak one( 17.25) fresh leaf a lowest one. The highest content is primary... |
