Dynamic Variation Of Flavone And Flavonol Glycosides In Longjing Tea During Manufacturing And Their Extracting Characteristics

Tea taste is an essential aspect of tea quality, there are many literatures have found that, catechins, caffeine and amino acid are important taste contributors to tea infusion. With the development of instrumental analysis and experimental techniques, people have learned much more about tea taste and paid more attention to other low content compounds which were ignored in the past, such as flavone and flavonol glycosides. This study proposed a standardrized profiling method based on high performance liquid chromatography combined with ultraviolet (UV) to quantify 11 flavone and flavonol glycosides in tea with references, then analysis the content of flavone and flavonol glycosides in fresh leaves of different tea variety, dynamic variation of flavone and flavonol glycosides during longjing tea manufacturing from fresh leaves to dry tea. In addition, the study also quantify extracting characteristics of flavone and flavonol glycosides in longjing tea under different brewing conditions, and their taste contributions were estimated by Dot factor (Dose-over-Threshold). The result showed that:1. Optimized HPLC-UV analysis method:mobil phase A (acetonitrile:formic acid: water, 3:0.15:96.85, v:v:v),and mobile phase B (acetonitrile:formic acid:water,30:0.15:69.85, v:v:v), gradient elution:0～23 min,0%B; 23～30 min,0%～50%B; 30～40 min,50%～62.5%B; 40～45 min, 62.5%～80%B; 45～48 min,80%-100%B; 48～83 min,100%B; 83～85 min,100%～0%B. Flow rate of 1 mL/min, colume temperature was at 25℃, injection volumn was 20μL, detection wavelength was 360nm. Based on this HPLC method, flavone and flavonol glycosides in tea can be almost exactly quantified with reference compounds.2. Flavone and flavonol grycosides vary with the maturity in different part of shoots of tea varieties. The content of Myr-rha&Que-gal rranked the first in fudingdabai tea variety, pingyangtezao tea variety and zhenong113 tea variety; the contents of Kae-gly and Myr-gly almost peaked at the first leaf, the content of Api-gly peaked at the third leaf while Que-gly peaked at leaves generally. In longjing43 tea variety, the difference of contents of top flavone and flavonol glycosides significantly differed from the other three tea varieties. Except Kae-gal, Myr-gal and Que-rut, the contents of other flavone and flavonol glycosides were less than other three tea varieties. However, the content of Que-rut in longjing43 tea variety was 171.1% 185.4% times higher than that in fudingdabai and zhenong113 tea variety, respectively.3. During longjing tea manufacturing, (1) Despite a slight fall after pan-fried, the content of flavone and flavonol glycosides increased on the whole; (2) Except Kae-gly, the contents of Myr-gly, Que-gly, Api-gly and total amount of 11 flavone and flavonol glycosides all increased in different extent, and all the rates of change of contents of flavone and flavonol glycosides were less than 10% during tea manufacturing with a few exceptions. (3) The proportion of Myr-rha (3.039-3.471mg/g) and Myr-gal (2.933-3.183mg/g) occupied in total amount of 11 flavone and flavonol glycosides were beyond 50% all the time, and with the ongoing manufacturing, they contributed the lagest part to the increment of total amount with 0.645mg/g.4. As the extracting experiment of flavone and flavonol glycosides indicated, (1) In traditional brewing conditions, Myr-gal and Que-rut were principalflavonolglycosides in longjing tea. With brewing temperature and time rising, eleven flavone and flavonol glycosides except Kae-rut increased variably. Que-rut and Que-gal leached faster, while Myr-rha and Vit-rha leached slower among 11 flavone and flavonol glycosides; (2) All of the Dot factors of Que-rut, Que-gal and Myr-gal outweighed 10, according to the definition of Dot factor, they may be significant contributors to tea taste; (3) In sensory evaluation, although Myr-gal’s Dot factors was from 5.89 to 6.90, there were no significant correlation with astringency or bitterness; While Vit-rha’s Dot factors was only from 0.34 to 0.44, there were significant correlation with astringency (r=0.88, P<0.01) and bitterness (r=0.90, P<0.01); Que-rut were significantly negatively correlated with both astringency and bitterness of tea infusins: Dot factors of flavone and flavonol glycosides can’t entirely represent the contributions they did to the astringency or bitterness of tea infusins, which may be affected by other tastants, such as catechins and so on; (4) Though the Dot factors can’t be calculated, Myr-rha, Que-rha and Vit were all significantly correlated with the astringency and bitterness of tea infusins.