Effect Of Ultrasound-enzyme Technology On The Flavor Of Black Tea Beverage

At present,black tea has the largest production in the world and the most widely consumed areas.In the meanwhile,black tea beverage is the mainly tea beverage type in global market.The anti-browning and anti-browning technology of black tea beverages have been relatively mature,and the study focused on the tea cream and aroma protection.Most of tea beverage producers remove tea sediment or inhibit tea sediment formation by physically removal or chemically de-creaming.When it comes to the fragrance and aroma protection,the main raw materials through the blending,aroma strengthening and protection,aroma extraction and recovery technology.P-glucosidase used on the hydrolysing terpene alcohol glycoside-precursor,as well as tannase on the tea cream removing have been reported in the literatures.A large number of studies also show that the ultrasound is helpful to industrial production though improving the catalytic activity of the enzyme reaction,and the reaction efficiency.Based on the advantages of enzyme and ultrasonic technology,the effects of ultrasound-enzymatic including tannase and ?-glucosidase on the influence of the main chemical components of black tea beverage,including teapolyphenols,catechins and theaflavin,and the aroma components were studied in this thesis.The optimum parameters of improving the flavor quality of black tea beverages has been provided.The main results are as follows:1.The effect of the treatment with tannase only on the flavor quality of black tea beverage were studied.The results showed that when enzyme concentration of tannase concentration was 0.04 U/mL and reaction time was 1 h,the color of the black tea beverage was bright and stable,and the stability was better,relatively.When the enzyme concentration of ?-glucosidase was 0.02 U/mL and the reaction time was 1h,the aroma of the black tea beverage was pure,and the flavor is moderate.2.The effect of the treatment with tannase,and ultrasonication continuously on the transmittance of black tea beverage was studied.The results showed that the transmittance of the samples increased significantly(P<0.05),compared with the group treated with tannase only.The Processing time was reduced to get the best transmittance,even though the same transmittance would reach while the group treated with tannase only.3.The effects of tannase and ?-glucosidase with the assistance of ultrasound on the flavor quality of black tea beverage were studied.The results showed that the transmittance of the black tea beverage after tannase ultrasonic co-treatment was the maximum when the reaction conditions were ultrasonic power 125 W and time 20 min.The black tea beverage has a good stability and taste.It shows a pure aroma while the black tea beverage co-treated with ultrasound and ?-glucosidase under the conditions of ultrasonic power 125 W and processing time 30 min.The optimum parameters for a bright color,pure aroma and good stability were 0.04 U/mL tannase,0.02 U/mL ?-glucosidase,ultrasonic power 125 W,reaction time 30 min.4.The change of physical and chemical indexes of ultrasound-enzyme(tannase and ?-glucosidase)treatments under different storage conditions were studied.The results showed that with the increasing storage temperature,the transmittance of each treatment group increased slowly,while the transmittance from the group co-treated with ultrasound-enzyme was very stable and more bright.The transmittance from the group co-treated with ultrasound-enzyme showed a high level compared to that from untreated group,in spite of it's transmittance decreased in a narrow range during the storage period.Quicker descending trends in tea polyphenols was seen in the group co-treated with ultrasound-enzyme in compared to the control group.The aroma,taste and color of each treatment group decreased slowly during the storage period,while the total sensory assessment score kept relative low level in the untreated group.