Study On The Processing Technology Of Stevioside Rich Stevia Tea

As the herbaceous plant, stevia belongs to the wild compositae family and is native to Paraguay, which is famous for its high stevioside content. The saccharinity of the stevia is 250～300 times the sucrose, while the calorific value is only 1/300 less than sucrose. With this advantage, the stevia is considered as the "natural saccharin" and "the best natural sweetener". Many studies show that, as the stevioside does not involved in the metabolic processes of the human body, after intake, it will not result in the increasement of blood glucose concentration nor insulin concentration within blood. And, if taken after lunch, it can obviously shorten the increase range of blood sugar, which can be used as an adjuvant therapy for the diabetes. In addition, the stevioside can adjust the blood lipid metabolism, nourish the spleen and stomach, and increase the assimilation of mineral substance. It is also can be used as an adjuvant therapy for hypertension and obesity. Today,consumers tend to enjoy tea which is pure natural, high quality, sanitarist, multifarious and with unique flavor. Thus, it is necessary to develop the stevia tea to satisfy the society requirement. Based on this situation, experiments with stevia leaf were conducted to study the processing technology of the stevia tea. The extraction technology of stevia tea was also studied. The results of this study are as follows:(1) Orthogonal experiments with stevia tea were conducted to study the extraction process of stevioside (stevioside, rebaudioside A, total stevioside). It was shown that the most suitable process is:the extract liquor is water, extract temperature is 60℃, extract time is 4 h, ratio of solid to liquid ratio is 1:45 and extraction frequency is two times.(2) Spreading can increase the content of amino acid, extract and stevioside, while it can reduce the content of flavonoid and chlorophyll. Thus, studies on the effects of different spreading time on stevia tea’s scent, flavor and infusion were conducted. It is obtained that when the spreading time is 6 h, we can get the highest content of stevioside, rebaudioside A, rebaudioside C and total stevioside. And, the content of stevioside, rebaudioside A, rebaudioside C and total stevioside with 6h spreading time are 30.30%,1.17%,29.12% and 3.58% higher than that without spreading, respectively. In addition, the tea gets the best sensory evaluation with 4h spreading time, while it gets a little worse sensory evaluation with 6 h spreading time. After overall analysis of the stevioside content and sensory evalution, together with other chemical quality indicator, we consider the most suitable spreading time is 6 h.(3) According to the study of the roller stir-fry under different time and different temperature, the most suitable roller stir-fry process was obtained like this: the temperature is 320℃ and the time is 210 s. Orthogonal experiments using the microwave stir-fry were also conducted. The most suitable conditions for microwave stir-fry are like this:the firepower is high fire, time is 5min and the dose of the material is 100 g. Compared roller stir-fry process with microwave stir-fry process, we find that with roller stir-fry process, we will get 0.90% higher stevioside, 3.00% higher rebaudiosid A,13.20% higher rebaudiosid C,5,00% higher total stevioside and 4.29% better sensory evaluation than the microwave stir-fry, respectively. After overall analysis of these indicators, we consider the roller stir-fry technology is better than the microwave stir-fry technology.(4) Rolling can increase the content of carotenoid and extract in the stevia, making the stevia tea in a good shape. The results show that, using the stevioside content and sensory evaluation as the evaluation indicator, rolling for 10 min can get the best quality stevia tea.(5) Studies on the effects of different drying temperature and different drying form on the stevia tea quality were conducted. The results show that when the drying temperature is 100℃, we can get the highest content of stevioside, rebaudiosid A and total stevioside, with their percentage in the stevia tea are 1.41%,16.851% and 19.801%, respectively. Furthermore, after being dried, the tea has dense scent, bright infusion and pure flavor.