Ultrasound-assisted Extraction Process of Glycosides from Stevia Rebaudiana Bertoni Leaves

Stevia Rebaudiana Bertoni leaves contain glycosides that have a sweetening power of 100 to 300 times greater than sucrose. These glycosides are increasingly used as natural sweetener, mainly to replace aspartame, in order to reduce daily caloric intake. The two major glycosides are Stevioside and Rebaudioside A, which represent about 90 % [w/w] of total Steviol. The Rebaudioside A is the most interesting since it has the advantage of not having a bitter aftertaste, unlike stevioside. In recent years, the cultivation of organic stevia is growing in the Occitanie region in France. Thus, the valorization of this production chain is of economic interest for this region. It’s known that conventional extractions to obtain these glycosides are time consuming and the extensive use of organic solvents may be harmful for human health and environment. Thus, the objective of this work was to develop a green extraction process suitable for industrial purposes, using water as solvent and ultrasound technique to obtain high yield of glycosides in the Stevia extract. The extractions are carried out in batch with recirculation and continuous assemblies at 45 °C. The effects of ultrasound power (at 20kHz), experience time/ residence time, and leaves concentration are studied. The soluble solids and stevia glycosides concentration are analyzed respectively by °Bx and HPLC. With the continuous assembly the experiments were carried out at 64 W and 144 W, which represents 50 % and 100 %, respectively, of the generator capacity. A low flowrate (or high residence time) is detrimental to the use of ultrasound, leaves sedimentation and their accumulation prevents probably the ultrasound diffusion in the medium, harming the steviol extraction. The extraction ultrasound-assisted allowed to increase in 9-10 % °Bx concentration for batch and continuous assembly, compared to extraction without ultrasound under the same conditions. Soluble species other than steviols are extracted with ultrasound. The HPLC results showed that the ultrasound favored lightly the extraction of stevioside.Key-words: continuous extraction, green extraction, sweeteners.