Research On The Changes Of Volatile Compounds Of Jasmine Tea During The Scenting Process And Technology Improvement

Jasmine tea has a long history of production, and is popular in daily consumpution, with the largest production and sale among traditional scented tea in China. The orthodox scenting technology is the mainly method of jasmine tea manufacturing, but there are also some shortcomings in it, such as complicated processes, great labour intensity, high energy consumption, long production period. In order to overcome these shortcomings, tea scientific and technical workers of our country, especially jasmine tea researchers have been trying to improve the orthodox scenting technology. This research analyzed the optimal extraction conditions of HS-SPME method, and the volatile compounds, the main quality components and economic benefit during the orthodox and isolated scenting process, and dicussed the effect of the water content of tea dhool, the rate of jasmine flower to tea dhool (RJF), the drying temperature and the scenting time on jasmine tea aroma quality.1. This experiment selected the tea content, extracted temperature and extracted time to analyze the optimal extraction conditions of HS-SPME method using dry-tea aroma method. The results showed that the best extracted conditions are selected as following:2.5g-5g of dry tea sample was transferred to a50-mL glass septum vial, and SPME fiber coated with65-μm polydimethylsiloxane/divinylbenzene (PDMS/DVB) was rapidly inserted into the headspace of the vial. The extraction was kept at40℃-60℃water bath and lasted for60nm2. The contents of volatile compounds during the orthodox and isolated scenting process were determined, the results snowed that16olefins,10esters,7alcohols,4nitrogenous compounds and3ketons were detected during the scenting process. The proportions of the five varieties were similar in2013and2014. The sum of relative contents of alkens and esters was up to70%, and that of alcohols and nitrogenous compounds was about25%, and the relative content of ketons was the lowest. The relative content changes of the five varieties were consistent There was little difference of the relative content of alkens during the orthodox and isolated scenting process. Compared to the orthodox scenting process, the relative content of alcohols during the isolated scenting process was7.75%and4.73%higher in2013and2014respectively. The relative contents of esters and nitrogenous compounds were both higher during the orthodox scenting process. The relative content of ketons was low, and it didn’t change regularly during the two years. The relative content of olefins increased during the scenting process, while it decreased after drying. The relative content of alcohols decreased, and that of nitrogenous compounds during the scenting process. And the relative content changes of esters and ketones were little.3. The changes of chemical composition had the same trend during the orthodox and isolated scenting process. The content of water extracts increased by1.90%-3.28%during the scenting process, those of tea polyphenols and amino acid were similar with and without scenting, and that of catechins decreased by9.90mg/g-20.30mg/g after scenting. The increase of moisture content and water extracts content during the isolated scenting process was less than that during the traditional scenting process. Compared with the traditional scenting process, energy consumption was bwer, the utilization of jasmine flowers was higher, the production cycle was shorter (take2-scentings for instance, the production period can be shorten by2-4days), and the cost was lower (4.62yuan could be saved of1kg jasmine tea product) during the isolated scenting process.4. The effects of the water content of tea dhool, RJF, the drying temperature and the scenting time on the aroma quality of jasmine tea during the isolated scenting process were studied in this experiment The results showed that, when the scope of water content of tea dhool was3.69%-8.39%, the content of volatile compounds increased with the increasing of the water content However, when the water content of tea dhool is above10.96%(10.96%-13.54%), the content of volatiles decreased. Thus, the appropriate water content of tea dhool wass8.39%-10.96%.When the scope of RJF was39%-86%, the content of volatile compounds in the jasmine tea increased with the increasing of RJF. In order to obtain jasmine tea product of high aroma quality, the RJF recommended was86%during the isolated scenting process. Overall, there was little difference among the content of volatile compounds in jasmine tea at different drying temperatures(80℃,100℃and120℃). In consideration of saving time, the drying temperature recommended was120℃during the isolation scenting process.Within3h-15h, the content of volatile compounds in jasmine tea increased with the increasing of time. Therefore, a long scenting time is good for the improvement of jasmine tea aroma quality during the isolated scenting process.