Variation in steviol glycoside contents of stevia (Stevia rebaudiana) leaves under various leaf drying processes

Stevia (stevia rebaudiana) leaves contain valuable sweet compounds, called steviol glycosides (SVglys), which the quantity and quality of these sweet compounds may be changed during the leaf drying process. The present study was conducted to survey the SVglys changes during different leaf drying methods applied for stevia leaves. The stevia leaves were similarly harvested before flowering and dried by different methods including oven (45 and 75 ˚C), shade, infrared, microwave, sun, and freeze-dry, and thereafter the SVglys were assessed. The results showed that the SVglys content and its compositions such as stevioside (Stev) and rebaudioside A (Reb A) were significantly affected by leaf drying methods. The highest content of SVglys and Stev was stabilized using infrared, microwave, sun, and freeze-dry methods while the other methods showed a lower content of SVglys and Reb A. The significant high content of Reb A was recorded by freeze-drying and sun methods. Our results conclusively showed that freeze-dry and sun drying methods were seen more effective than other drying methods in SVglys retention in leaves and recorded the lowest SVglys losses during the drying process.