Study On The Changes Of Main Chemical Components During The Processing Of Taiping Houkui Tea

Taiping Houkui tea,one of ten top famous teas,is produced from the local tea plant population at Huangshan district(former Taiping county),Huangshan city,Anhui province.It is manufactured by the processes of picking of young shoots,spreading,enzyme inactivation,slightly press shaping and roasting.The sensory quality includes the flat and straight appearance with two leaves and one bud,a stout and heavy body,a palegreen color,a lasting and refreshing orchid-like aroma and a mellow and sweet taste.In this paper,the effects of different fixation methods of fresh tea shoots on the contents of main components were explored to find out the rapid approaches for the fixation.Then,we studied the distribution of main chemical components in different parts of fresh tea shoots.Lastly,the changes of the main components were determined and analyzed in every processing stage of Taiping Houkui tea.Results achieved in this paper are as follows.In the six fixation methods of fresh tea shoots,the fixation by liquid nitrogen plus lyophilization could maximally retain their main quality components.However,the fixation by microwave and roasting at 60~80oC is rapid and easily operated with simple apparatus to treat the fresh shoots especially in onsite processing room.The main quality components such as total catechins,caffeine,epigallocatechin gallate and theanine can reach to the average amount of the shoots among the six fixation methods,while total polyphenols and free amino acids is slight high than the samples in the other five methods.The fixation by microwave and roasting at 60~80oC is a practical method for the analysis of the quality components of fresh tea shoots.In the young tea shoots of Huangshan tea plant population,the total polyphenols,catechins,and caffeine are decreased gradually from 23.22±2.24%,25.06±2.67%,6.09±0.37% to 18.03±1.34%,15.72±2.97%,3.45±0.15% respectively in the order of bud,the first leaf,the second leaf,the third leaf and tender stem.The total free amino acids are higher in buds with the amount of 3.33±0.26% and gradually decreased to the least amount of 2.84±0.15% in the third leaves,but those in tender stem are highest up to 3.73±0.31%.Among total free amino acids,theanine is the highest amino acid accounted for 48~67% of total.During the processing of Taiping Houkui tea,the total amount of tea polyphenols and catechins are gradually decreased from spreading to roasting.Especially,the amount of tea polyphenols are decreased significantly in the process of press shaping and roasting,while the amount of total catechins especially EGCG and ECG are degraded significantly in the roasting process.However,caffeine and theanine are stable and shown insignificantly changes during the whole processing.Notably,the total amount of free amino acids was increased significantly during the process of roasting.This may be contributed by the hydrolysis of proteins and polypeptides and the increase of lysine,phenylalanine,serine,aspartic acid,isoleucine,leucine,tyrosine and valine.