Study On The Effects Of Cultivation Measures Of Stevia Rebaudiana Quality

Steviosides are Stevia's taste compounds. The main components of steviosides are stevioside(STV), rebaudioside C (R-C) and rebaudioside A(R-A). R-C is 40-60 times as sweet as sucrose. The sweetness of STV is 270-300 times that of sucrose, but tasted slightly bitter. R-A is 350-450 times sweeter than sucrose, tasted the best and the closest to sucrose. Because R-A is the best quality in the steviosides, increasing the proportion of R-A is improtant to improve the Stevia's quality. The main varieties of Stevia, tipping, microelements treatments, light controlling, harvesting and drying effecting on the main components of Stevia have been studied in the experiment. Test results are as follows.(1)The research on cultivation process shows that the quality of Shoutian-3 is the best. The content of R-A is 9.83% which is 14.44% and 12.47% more than Shoutian-2 and Runde. Its upper leaves is the best and its content of R-A is 11.53%.(2)Tipping two times on the cultivation is good for improving quality of Stevia. With this treatment Stevia's R-C, R-A, total stevioside, free amino acids and crude protein were significantly higher than other treatments. They were 1.12%, 10.01%, 12.24%, 4.98% and 19.8%.(3)R-A and total stevioside were incresed gradually in Stevia's growth process. The ratio of R-A in total stevioside was incresed from 75.46% to 85.21%. The ratio of STV and R-C in total stevioside were decented from 17.46% to 8.33% and from 6.89% to 6.47%.(4)Between the many treatments of manganese, the spraying of 3mg/g potassium permanganate in the early branching period was the best that R-A, total stevioside and free amino acids were all significantly higher than CK. They were 10.11%, 12.35% and 5.65%. Others qualities were no significantly with the CK. Compare to the other treatments Stevia tasted sweeter and fresher. Betweent the boric acid treatments, 0.5mg/g boric acid treatment in the early branching period was the best. With the treatment Stevia's R-A, total stevioside, free amino acids were all significantly higher than CK. They were 10.10%, 12.51% and 5.49%. Its crude fiber was significantly lower than CK which was 16.72% which was 0.77% lower than CK. But STV is not significantly different from CK. It tasted sweeter and more comfortable to eat than other treatments. Betweent the treatments of ammonium molybdenum, the treatment of 3mg/g in the early branching period perform better. Its R-A, total stevioside, free amino acids and crude protein were all significantly higher than CK. They were 10.43%, 12.32%, 6.14% and 20.93%. At the same time its STV was only 85% of CK. It tasted sweeter and more comfortable than other treatments. Between zinc chloride treatments, The treatment of 3mg/g in the branching period was better than other treatments. Its R-A and free amino acids were 10.13% and 4.77% which were significantly higher than CK. STV was 11.65% lower than CK, but crude fiber was also significantly higher than CK, high to 17.19%.(6)The study on the different shading time showed that covered one week with one layer was the best. Its crude protein was significantly higher than CK which was high to 20.06%. STV was lower than CK which was 0.84%. Free amino acids, crude fiber and R-A were not significant with CK. With the treatment Stevia's sweet was more comfortable. In the treatments of different shading layers, two layers showed better than other treatments. Its R-A, total stevioside free amino acids and crude protein were 9.47%, 11.55%, 5.31% and 20.16% which were significantly higher than other treatments. Its steviosides were not significant with CK, but its free amino acids, crude protein and crude fiber was significantly higher than CK.(7) It had better harvested before its lower leaves having fallen. In this time Stevia's R-A and total stvioside were in the highest level which were 10.54% and 12.37%. Drying research showed that low temperature(80℃) was good for retaining more R-A and total stevioside which were 7.77% and 6.50% higher than CK. At the same time its free amino acids and crude protein maintaine at a relatively high level.