Analysis On Metabolic Chemical Composition Of Keemun Black Tea In Processing

Keemun black tea is traditional Congou black tea of China.It mainly produces in Shitai,Yi country,Keemun country and Chizhou city,Anhui province.Keemun Black Tea is made of Keemun Chuye species leaves and processed fresh leaves of tea tree with the character of fresh and mellow taste,red-bright reflected by the leaves and rich fragrance and have gained popularity in many consumers.Keemun black tea processing procedures include withering,rolling,fermentation and drying.During the processing of the tea,the main chemicals in the fresh leaves have gone through a series of complicated changes of hydrolysis,oxidation and complexation.Therefore,maser of the metabolism rules of main chemicals and research on the changes of the main ingredients in the processing will play an important role in improving processing level of Keemun black tea and guaranteeing the product quality.Metabonomics is a kind of new technology for researching the metabolism method of biology system.In recent years,mass spectrometry,chromatography and their combined technology are widely used in metabonomics.This study takes the samples of Keemun black tea in the processing at various stages as material,using High Performance Liquid Chromatography(HPLC)to conduct quantitative analysis on the catechins,theaflavins,alkaloids,amino acids,flavonoids in the samples.Then utilize simultaneous distillation and extraction(SDE)to exact fragrance matters and analyze the fragrance component changes by gas chromatography mass spectrometry(GC-MS)for the purpose of searching the Metabolism Rules of main chemicals in the processing.It has made the following results through research:(1)During processing of Keemun black tea,metabolisms of catechin and theaflavin are highly correlated.The content of catechins is gradually reduced during the processing of Keemun black tea,where a sharp drop occurs in the process of rolling.As of the time when the leaves are dried,the total content of catechins only accounts for 8.72% in fresh tea leaves;however,the content of theaflavins is increased in withering and rolling processes,among which content of theaflavins is rapidly increased at rolling while being significantly reduced in the course of fermenting.As of the time when the leaves are dried,the total content of theaflavins are 24.97 times higher than that in fresh tea leaves;After Pearson correlation analysis is conducted against changes in the total contents of theaflavins and catechins,the results show a significant negative correlation at a significance level of 0.05(bilateral),with the correlation coefficient of-0.909.(2)Total content of amino acids is reduced during the processing of Keemun black tea and changes in 18 types of amino acid contents are present with polarization trend.7 amino acids is reduced during the processing,relevant named theanine,histidine,glutamic acid,methionine,aspartic acid,arginine and cysteine.9 amino acids see a rising content during the processing,relevant named serine,glycine,proline,tyrosine,valine,lysine,isoleucine,leucine and phenylalanine.Threonine and alanine show no significant change in comparison with those in the fresh tea leaves.Proline is accumulated in large quantities during the processing and the results of vitro laboratory experiments cannot well prove that generation of proline is sourced from metabolism of glutamic acid and arginine.(3)Aromas of Keemun black tea are composed of linalool,linalool oxide,benzene ethanol,geraniol,phenyl acetaldehyde,geranic acid,benzoic acid and salicylic acid methyl ester,which are mainly the products of glycoside hydrolyzation.Activity of glycoside hydrolase is strengthened during the withering.Hydrolyzation of flavor precursors and controlling of withering process are critical toflavor formation of Keemun black tea.