Study Of Polyphenol, Caffeine And Antioxidant Activity Under Various Tea Brewing Conditions

Tea has become more and more popular all around world because of its pleasant aroma, unique taste and potential health-promoting properties. However, the purpose of drinking tea is just to add moisture to improve the taste, but neglecting the intake of biologically active ingredients.This research chose green tea, black tea, oolong tea and rosebud as experimental materials according to its fermentation degree. The experimental factors are: temperature, liquid-solid ratio, time, brewing times, container, whether covered and stirred. According to single factor experiments, a mathematical model was established by using Box-Behnken central composite experimental design. Meanwhile, by combining with the results of high-performance liquid chromatography experiments and antioxidant experiments in vitro to verify and refine the conditions.The conclusion included aspects such as the optimum brewing conditions of polyphenol contents, the optimum process conditions of caffeine contents for work group, brewing ways and types of tea for special groups. In addition, the study was investigated the effect of antioxidant activity of black tea with sugar added.The study showed that the optimum process conditions on the polyphenol contents of green tea were as follows:temperature 81℃, liquid-solid ratio 150mL/g, time 7min, and verified value 112.80mg/g. The conditions of black tea were as follows: temperature 93℃, liquid-solid ratio 200mL/g, time 5.5min, and verified value 59.48mg/g. The conditions of oolong tea were as follows:temperature 94℃, liquid-solid ratio 120mL/g, time 7min, and verified value 23.06mg/g. The conditions of rosebud were as follows:temperature 91℃, liquid-solid ratio 210mL/g, time 11min, and verified value 12.11mg/g.The study showed that the optimum process conditions on the caffeine contents of green tea were as follows:temperature 88℃, liquid-solid ratio 220mL/g, time 6min, and verified value 32.36mg/g. The conditions of black tea were as follows: temperature 85℃, liquid-solid ratio 200mL/g, time 5min, and verified value 35.56mg/g. The conditions of oolong tea were as follows:temperature 94℃, liquid-solid ratio 210mL/g, time 7min, and verified value 11.15mg/g.The effect of habitual factors can be used as a reference. It significantly increased the contents by using heat preservation cup or stirring. The antioxidant experimental results indicated:the content of polyphenol is positively correlated with the scavenging rate of ·OH. The change trend of tea polyphenol contents was consistent in both the scavenging rate of ·OH and DPPH·. Hence, the optimum brewing conditions had practical significance. By reducing the range of temperature, time and liquid-solid ratio, active ingredients were analyzed and the changes were slightly different from tea polyphenol contents. So it was adjusted appropriately based on personal habitual. Various groups prefer different types of tea based on its characteristics:green tea with higher content of catechins, black tea with higher caffeine content, oolong tea with intermediate contents of catechins and caffeine, rosebud with no caffeine detected. With the increase of amount of black tea with sugar, antioxidant activity is decreased. Thus, the sugar addition should be controlled within 5g/L.