Study On The Variation Of Volatile Substances And Quality Components In Congou Black Tea During Fermentation Process

Fermentation is the critical process of black tea production and plays an important role on the quality formation of black tea. The research object was the process of black tea fermentation, study the change of volatile substance during the fermentation process in different conditions by establish the analysis method, and build the correlation model of quality change and moderate fermentation of black tea fermentation procedure.1. Comparing the type and number of volatile substances extracted by two methods, simultaneous distillation extraction and headspace solid-phase microextraction. Twenty-eight and 36 types of volatile substance was identified by simultaneous distillation extraction and headspace solid-phase microextraction respectively. The former method extracted substances mainly were low boiling point of alcohols, aldehydes, ketones and weak polar olefin. While the later method extracted volatile substance not only contained low boiling point of alcohols and aldehydes, but also high boiling point of the furan,benzene-contained compounds, naphthalene-contained compounds, and secondary product produced by thermal chemical action.2. Researches on condition optimization of the method of extracting volatile substances-headspace solid-phase microextraction. Based on the extraction of peak area and confirmed volatile substances, by changing the tea-water proportion, extraction temperature and time, we obtained the best extraction method of volatile substances: Accurately weighed grinding tea sample by freeze drying1.00 g in a 80 mL sample bottle, add 3 mL boiling ultrapure water, tea-water proportion was a third(g/m L), affix a seal, balance at 60℃ water bath pot for 5 min, solid phase micro-extraction adsorption for 60 min,obtained the extrat for GC- MS analysis. Under the conditions of this method, the volatile substances of congou black tea could be detected effectively according to the extraction of peak area and confirmed volatile substances.3. The trend of the type, number and relative content of volatile substances change was studied.The results indicate that the types of volatile substances was first increase and then decreased as the extension of time during the fermentation procedure. From the quantitative aspect, alcohols, aldehydes,olefin and olefine were stay at a higher level in the whole fermentation process, and the number of alcohols and aldehydes has a tendency to shift. From the relative content aspect, the alcohols were the highest with a average number above 45%. It continued on decreasing from 56.9%(0h) to 48.7%(5h).The relative content of esters was also decrease from 20.4%(0h) to 12.5%(5h). However,aldehydes volatile substances showed opposite change tendency, increased 12.1%(0h) to 22.3%(5h).The relative content of volatile substances such as acids, ketone, olefin maintained steady with little changes.4. In order to study the relationship among quality components, sensory evaluation and optimum fermentation of congou black tea, exploring the discrimination criterion of optimum fermentation. We conducted sensory evaluation and tested 10 quality components such as total catechin, EGC, EGCG, EC,ECG, GA, L-C, TFs, TRs, TB and so on. Analyzing the inner connection about quality components of congou black tea via dynamic clustering analysis, and classify the test samples according to the degreeof fermentation, then comparing with the fermentation degree results of sensory evaluation,understanding the contribution of each quality components through variance analysis. Jaccard coefficient based on quality components and sensory evaluation insufficient fermentation, optimum fermentation and over fermentation samples were Jb=0.82, Js=0.59, Jg=0.65 respectively. The contribution of quality components to the classification was, EC> total catechin> EGCG> ECG> L-C>GA> EGC> TB> TFs> TRs. Quality components present linear change in different types. It is concluded that, according to the quality components variances of different fermentation degrees of congou black tea, it is feasible that using dynamic clustering method to discriminate optimum fermentation, and the classification results is desirable. The content change of total catechins and its components, as well as theaflavin in different fermentation degree of congou black tea could be used as discrimination criterion of optimum fermentation.