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Hua J.,National Engineering Technology Research Center for Tea Industry | Yuan H.,National Engineering Technology Research Center for Tea Industry | Yin J.,National Engineering Technology Research Center for Tea Industry | Jiang Y.,National Engineering Technology Research Center for Tea Industry | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

Enzyme deactivation is the key process of green tea primary processing, which has significant effects on the color, aroma, taste and other flavor quality of green tea. In the process of enzyme deactivation, high temperature is used to rapidly destroy enzyme activity to stop the oxidation of polyphenols and prohibit leaves to become red, and to evaporate water in the leaves to increase flexibility of the leaves and create opportune conditions for the subsequent modeling. In addition, the volatilization and conversion of some undesirable low-boiling aromas occurs under high-temperature treatment, and meanwhile, the formation of some new special aromas improves the tea fragrance. Different ways of enzyme deactivation show different effects on the various quality materials of fresh leaves and the quality of made tea, for example, microwave deactivation of enzyme can rapidly inactivate enzymes, and make the color green, but the taste and fragrance are poor; enzyme deactivation with hot air can make the excellent fragrance due to high temperature, but can easily lead to the coke side and focal point; traditional roller deactivation of enzyme can make high fragrance and pure taste of tea, but it is not easily controlled. For this reason, based on roller deactivation of enzyme, the machine used in the article combines the advantages of different manners of enzyme deactivation. Electromagnetic roller-hot air coupling machine of enzyme deactivation is heated by electromagnetic heat technology, which significantly improves energy efficiency and heating stability. The thermal efficiency of the enzyme deactivation machine is more than 45%, and the temperature fluctuations can be controlled under ±3℃. The digital regulation system is used to improve the uniformity and stability of enzyme deactivation, and automatic sending and continuous production of leaves can effectively reduce the labor and employment. The coupling technology between roller deactivation of enzyme and hot air deactivation of enzyme makes green color and overflowing fragrance for leaves, and the sensory quality of made tea is better than microwave deactivation of enzyme and electric heating tube roller deactivation of enzyme. The structure composition and technical characteristics of this enzyme deactivation machine (Patent number: ZL201410473680.9) were introduced in this article. Then the parameters of the electromagnetic roller-hot air coupling enzyme-deactivation of green tea were optimized. Based on the results of previous single factor experiments, taking main biochemical compositions' contents and sensory evaluation scores of made tea as investigation indices, Box-Behnken design was used to optimize the parameters of enzyme deactivation process (temperature of hot air, wind speed of hot air, temperature of front part, etc.) with electromagnetic roller-hot air coupling machine. And the new technology of enzyme deactivation was compared with electric heating tube roller enzyme deactivation, microwave deactivation of enzyme, hot air enzyme deactivation and electromagnetic heat roller enzyme deactivation. The results showed that when the leaf weight of enzyme deactivation was 150 kg/h, the optimal combination parameters of electromagnetic roller-hot air coupling machine of enzyme deactivation were determined as follows: temperature of hot air was 104℃, blower speed of hot air was 920 r/min and temperature of front part was 270℃. The taste, color and aroma of green tea made with these parameters were the best and sensory quality score was 91.0, which was 2.7-4.0 point higher than other methods of enzyme deactivation. And the contents of tea polyphenols, amino acids, soluble sugar, catechins, caffeine and flavonoids of leaves after enzyme deactivation reached 13.849%, 2.057%, 8.412%, 9.724%, 2.172% and 1.336%, respectively. The energy consumption was reduced by 1/2 compared with electric heating tube roller enzyme deactivation, and the thermal efficiency was up to 45%-55%. The deficiency of traditional roller enzyme deactivation can be overcome with electromagnetic roller-hot air coupling enzyme deactivation technology, which will provide guidance for the production of green tea. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved. Source


Hua J.,Chinese Academy of Agricultural Sciences | Hua J.,University of Chinese Academy of Sciences | Hua J.,National Engineering Technology Research Center for Tea Industry | Hua J.,Key Laboratory of Tea Biology and Resources Utilization Ministry of Agriculture | And 19 more authors.
Journal of Chinese Institute of Food Science and Technology | Year: 2016

To research the effect of withering oxygen concentration on dynamic change of main biochemical components and enzymatic activity of tea fresh leaves, using of a leaf and a bud shoot as fresh tea leaves material, setting three different withering oxygen concentration, sampling withered leaves with different moisture content, rolled leaves, fermented leaves and fired tea, then the contents of tea polyphenols, total amino acids, flavonoids, soluble sugar, caffeine, total soluble solid, catechin components, PPO activity, and POD activity were determined, and the effects of different withering oxygen concentration on tea pigments and sensory evaluation of fired tea were also analysed. The results showed that with the gradual decline of moisture content in tea processing, the contents of tea polyphenols, total amino acids, flavonoids, soluble sugar, caffeine, total soluble solid and catechin components decreased gradually, and the content of flavonoids and caffeine were rising. In the withering process, the contents of polyphenols, amino acids and flavonoids decreased at first, then increased; the polyphenol oxidase activity and the contents of soluble sugars and total soluble solid decreased gradually; the peroxidase activity and the content of caffeine increased gradually; the content of conventional biochemical composition in final withered leaf and fired tea were positively correlated with withering oxygen concentration; the contents of ester type catechin components and total catechin were the highest at 40%O2, and the lowest at 59%O2; PPO activity was the lowest at 59%O2, and had no difference the other two treatments; POD activity were positively correlated with withering O2 concentration. The contents of theaflavins components, thearubigins and sensory evaluation scores in fired tea were the highest at 59%O2 treatment, and the lowest at 59%O2 treatment. © 2016, Chinese Institute of Food Science and Technology. All right reserved. Source

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