Studies On The Methods For Fingerprinting Technology And Quality Evaluation Of Tea

Tea is one of the most popular beverages in the world,and has great economic value.However,quality control of tea has been focused on monitoring toxic elements and pesticides residues up to now.It's very important to improve the methods for quality evaluation of tea.In this thesis,new method for tea components,such as volatile compounds,soluble components and heavy metals analysis was developed.The possibility of using some components as the indicators for quality evaluation of tea was discussed based on a large numbers of samples.The application of fingerprinting technology in tea analysis was put forward aiming at the development of better quality control methods for tea.The development of an HS-SPME-GC-MS method for determination of volatile organic compounds in tea was described.Three-dimensional GC-MS fingerprints of 65 tea samples were characterized,reflecting the distribution of various types of tea volatile components.The eight categories of volatile components,including alcohols,hydrocarbons,esters,ketones,nitrogen-containing compounds,aldehydes,acids and ethers,were analyzed.Different kinds of tea have its major components of the aroma,which characteristic the tea flavor.Some of the volatile compounds can characterize the class information of tea.The system provides possibility to assess the quality difference of tea without standard.The HPLC method of eight catechins and three alkaloids in tea was improved.The methods of sample preparation and instrument conditions were optimized.This method has been applied for the analysis of 65 tea samples.With the increase of fermentation,the content of epicatechin compounds reduced.As the degradation product of GCG,GC was most concentrated in oolong tea.The dissolution of catechins and alkaloids during the process of making tea were studied.The maximum concentration of soluble components was in the second tea.The concentrations of 34 kinds of mineral elements were determined by ICP-MS.The results showed that different types of tea have their respective advantages and origin of the metal ions.The Pb contents of all samples complied with the standard requirements,but total rare earth oxides contents exceed the standard requirements in some oolong tea.The causes of excessive rare earth oxides were analyzed.The dissolution of rare earth element and Pb before and after the process of making tea was studied.Dissolution rate of rare earth oxides and Pb were 14.3% and 25.7%,respectively.Different classification models tea were established to distinguish the different types of tea.The models of cluster analysis and principal component analysis were not ideal.The method ofGA optimization of support vector machine achieved good result based on GC-MS and LC data.