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Yuan H.,Key Laboratory of Processing and Quality Control of Tea and Beverage Plants | Xu Y.,Key Laboratory of Processing and Quality Control of Tea and Beverage Plants | Deng Y.,Key Laboratory of Processing and Quality Control of Tea and Beverage Plants | Yin J.,Key Laboratory of Processing and Quality Control of Tea and Beverage Plants | Wu R.,Key Laboratory of Processing and Quality Control of Tea and Beverage Plants
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2013

Fixation is the key procedure of green tea processing, which significantly impacts the color, aroma and taste of green tea. Because traditional roller fixation machine was heated by firing coal, firing gas or electricity, there are many defects in thermal efficiency and temperature-control stability. Electromagnetic heat roller fixation machine was directly heated by electromagnetic heat technology, which significantly increases the energy conversion rate and heat energy utilization rate. The thermal efficiency of electromagnetic heat roller fixation machine is 50%~60%, the temperature drift range can be controlled under ±3°C, and it can synchronously measure and control the temperature of three parts (front, middle and back). The structure composition, operational principle and technical characteristics of a new-style electromagnetism heating roller fixation machine (Patent number: ZL201020157446.2) were introduced in this study. Then with the materials of fresh tea leaves (from one bud and one leaf to one bud and two leaves), the parameters of electromagnetic heat fixation processes of green tea were optimized. Based on the results of single factor experiments, the orthogonal experiments of four factors including front part temperature (240°C, 270°C and 300°C), middle part temperature (220°C, 250°C and 280°C), back part temperature (190°C, 220°C and 250°C) and fixation time (90 s, 105 s and 120 s) were carried out. According to the weight coefficients of tea sensory test, tea polyphenols (25%), amino acids (25%), soluble total sugar (20%), catechins (20%) and chlorophyll (10%) were used as the evaluating indicators of green tea quality in the orthogonal experiments. Through comprehensive analysis, A2B3C1D1 (270°C, 280°C, 190°C, 90 s) was preliminarily considered as the optimum fixation parameters. But, due to that the temperatures between middle part and back part was too large, it may easily result in distortion of the roller and decreasing the homogeneity of temperature control and life length of the machine. To synchronously consider the mechanical function and the green tea quality, A2B2C1D2 (270°C, 250°C, 190°C, 105 s) was compared with A2B3C1D1. The results showed that there was no significant difference in chemical component contents and sensory quality, except that the aroma of green tea with A2B3C1D1 was higher than that with A2B2C1D2. Comprehensive analysis of chemical components contents of green tea, working performance and economic benefits, the appropriate fixation parameter of electromagnetic heat roller fixation machine is A2B2C1D2. Then the fixation with electromagnetic heat roller was compared with other fixation ways (traditional electroghermal heat roller fination, microwave fixation and high temperature hot wind fixation), the results showed that electromagnetic heat roller fixation exhibited high-efficiency (146 kg/h), low-cost (0.38 yuan/kg), easy control, high-stability and low-pollution advantages. And the green tea processed from electromagnetic heat roller had best sensory quality, the fixing leaves showed light fresh green, rich aroma. This study will help to enhance the fixation technology of green tea processing. 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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