| In recent years,with the character of easy to use and healthy,instant tea as tea processing product is more and more popular and favored by consumers.Instant tea,especially instant black tea is widely used in beverage applications.However,due to the quality of raw material,low processing yield and complicated processing steps,the lack of black tea aroma restricts the development of instant black tea.In this paper,to study the effect of tea roasting,enzymatic hydrolysis,extraction,filtration,concentration,drying and other key processing steps in the production process of instant tea on the aroma of black tea,BOP grade Ceylon black tea was used as raw material to explore the changes of aroma during the processing of instant black tea and provide theoretical evidence for the development of high-aroma instant black tea.The results are as follows:Titian tea roaster was used to in the process of black tea,with roasting temperature set at 70℃,90℃ and 110℃.Quality of black tea was tested from 0h to 9 h.Sample was taken once per hour.Sensory evaluator provide feedback on aroma,color and taste for each sample.HPLC was used for the determination of catechin level mainly for Catechin(C),Epicatechin(EC),Epicatechingallate(ECG),Epigallocatechin(EGC),Epigallocatechingallate(EGCG)content in tea Research results show that,total catechins were 1.11 times.It is concluded that tea quality could be better improved when roasted at 90℃ for 5 h.In the process of enzymatic hydrolysis extraction,through single factor and orthogonal experiments,effect of extraction rate of tea polyphenols and catechin was studied through the comparation of the use of different pectinase and cellulase,extraction temperature,extraction duration and enzyme amount.When 0.25%of complex enzyme containing pectinase B and cellulase A with mixing ration of 1:1 was added to the process,with the extraction temperature set at 45℃,and extraction duration was 120min,the extraction rate of tea polyphenols reached 90.52%,and the loss of aroma components caused by high temperature was avoided.The average level of EGC,C,EC,ECG and EGCG were 14.20%,6.89%,17.11%,13.68%and 16.17%higher than the average level of extract without enzymatic hydrolysis by HPLC.Vacuum concentration and reverse osmosis concentration(RO concentration)were used to compare and analyze the difference of the active substance and black tea aroma components through different concentration techniques.It is found that using RO concentration,tea polyphenols,caffeine and catechins level increased by 23.3%,8.6%and 12.3%,respectively comparing to vacuum concentration.Solid phase microextraction(SPME)and GC-MS detection method were used to detect the,aroma components black tea during concentration.Study shows that only 6types of main aroma components can be detected during vacuum concentration.31 types of aroma components were detected during RO concentration.,The total amount detected in RO concentration is 10 times more than vacuum concentration.Therefore,reverse osmosis concentration is more effective than vacuum concentration to retain the effective substances and aroma components in black tea.Vacuum freeze drying and spray drying techniques were used to produce instant black tea.The results show that the content of theanine in instant black tea powder produced by vacuum freeze drying was 149%higher than that produced by spray drying.The application of instant tea powder produced with the combination of the optimum techniques listed above was tested in powdered milk tea and liquid tea beverages.The powdered milk tea recipe was optimized through orthogonal experiment.To achieve the best combination of color,taste and aroma of milk tea,the recipe contains 45%white sugar,2.5%instant black tea powder,20%whole milk powder and 32.5%maltodextrin.Comparing with the product using conventional instant black tea products,the brightness,reddening and theanine of liquid tea drinks increased by 80.98%,57.69%and 73.44%respectively,and the turbidity decreased by 90.38%. |
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