Analysis On Chemical Components Of White Tea With Different Grades And Storage Times

White tea is one of the six tea categories and mainly produced in Fujian province of China.White tea is processed simply without fixation and rolling and is loved by many people all over the world because of its unique qualities.Nowadays researchers mainly focus on medical and healthy function of white tea,and ignore its chemical quality.25 white teas with different grades and stored times were analyzed by high-performance liquid chromatography(HPLC),and water extract,catechins,alkaloids and amino acids were compared.Volatile compositions of white tea were extracted using simultaneous distillation and solvent extraction and analyzed by gas chromatography and mass spectrograph(GC-MS)as well as investigating the main biochemical components in white tea for qualitative identification by UPLC-QQQ-MS/MS to analyze the effects of raw material grade and storage time on white tea chemical quality.This research results are of importance to guide the standardization of production and processing and reasonable storage of white tea.The results showed as the following:(1)There were differences in main chemical quality components among different grades of white tea.The contents of water extracts,total catechins,esterified catechins and three alkaloids decreased with grades reducing.The contents of non-galloylated catechins increased first and then decreased.The theanine content in Gongmei was significantly higher among all grades of Fuding white tea,and theanine content of Baimudan had the highest level in all grades of Zhenghe white tea.However,total amino acids contents in Gongmei reached the highest level in these two kinds of white tea.The results showed that51 volatile compounds were identified in four grades white tea and contents of alcohols,aldehydes,esters,acids and total volatiles in Baimudan were the highest among different grades.Alcohols and aldehydes were the major components among the compounds,among which the contents of linalool and its oxides and 2-hexenal were the highest.(2)Main chemical compositions in white tea degraded during storage.It was observed that contents of water extracts and catechins showed a similar tendency to decrease with storage times,while gallic acid and alkaloids increased with storing time.Most amino acids decreased with storage,but some amino acids,especially for methionine,increased in short-term storage.56 volatile compounds were identified in white tea stored for different times.Alcohols and aldehydes were still the principal aroma components.Most volatile compounds decreased with storing,while acids showed increase during storage.The oldwhite tea stored for 20 years contained high content of hexadecanoic acid,trimethylsilyl ester,cedrol,junipene and germacrene D.(3)Main chemical compounds in white tea were analyzed qualitatively by UPLC-MS/MS.29 peaks were obtained and 22 compounds were identified.Baihao Yinzhen produced that year contained abundant compounds.The old tea stored for 20 years had significantly higher theobromine.