Studies On The Technology To Optimize The Quality Of Instant Black Tea By In-vitro Oxidation With Polyphenol Oxidase

The study that polyphenol oxidase system oxidation in vitro from fresh leaves of different varieties tea trees and different varieties fruit was used to oxide green tea in order to get instant black tea were done to broaden the raw materials and improve the quality technology on instant black tea. Optimized parameters and supporting technology were proposed and a multifunctional enzyme reaction tank was designed according to the needs of the process. Then, a pilot-scale production was carried out to produce high quality instant black tea compared to black tea produced by the conventional process.The results were the followings:1. The enzyme source of polyphenol oxidase from fresh leaves of tea trees and fruits could promote the enzymatic reactions of tea polyphenol and was used to catalyze green tea to obtain instant black tea. Results showed that enzyme source A from fruits was the optimal and had the best catalyse capability; and enzyme source B from fresh leaves of tea tree was also a relatively optimal choice.2. Study on the effects of in vitro oxidization of polyphenol oxidase on conditions of different concentration of the enzyme activity, reaction temperature, reaction time and the oxygen quantity, with respect to quality of industrial production and feasibility economically, we concluded that with2%-3%tea soup, the ratio of enzyme source from fruit to the tea raw materials was between50%and100%, the temperature was38℃, the time of enzymatic reactions was60min, the oxygen quantity was1mL air/min (100ml tea soup).3. According to the optimal reaction conditions of enzyme source A of fruits, a multifunctional enzyme reaction tank was designed for technology needs and the relevant equipments were supported. Then, a pilot-scale production was carried out and instant black tea was produced. The content of the theaflavins (up to2.44%) was2.54times that of instant black tea produced from routine CTC broken black tea in Yunnan Province. The soup of the instant black tea looked pink and bright and smelled sweet with fruit and tasted good.4. The instant decaffeinated black tea was produced by using decaffeinated fried green tea from Zhejiang Province, with the enzyme source A from fruits as the oxidant. The instant decaffeinated black tea from Lin'an City, Zhejiang Province was used as the control. The product gained a score13.85higher than the control and the theaflavins content was6times (up to1.68%) as the control. The qualities of the soup were significantly improved on pinkness, color, aroma and taste.5.The fresh leaves of variety B tea tree from organic green tea plantation was used as enzyme source and was enzymatic oxidized.Then,we obtained cold soluble organic instant black tea. The quality score of the instant black tea was7.3points higher more than that of instant black tea from organic black tea from Lin'an City, Zhejiang Province, which was the control, and the content of theaflavins (up to1.8%) was12times that of the control. The soup was more bright red and intensity of taste was higher.The results showed that exploitation of polyphenol oxidase in vitro oxidation of extract of green tea could optimize the quality of the instant black tea. Especially, it was technologically and economically feasible to increase the content of theaflavins. The technology could promote the production of instant black tea and the use of summer and autumn tea and trimmed leaves. Therefore, we could make full use of the existing tea resources and increase the income of farmers.