In recent years, the rising rate of obesity and health problems associated with metabolic syndrome indicators (diabetes, cardiovascular, blood pressure) are turning consumers to exploring healthy, low-sugar and low-fat diets, as well as to using low-calorie sweeteners. In the current food market, sweeteners of synthetic origin, such as aspartame, sucralose, cyclamates etc. are available, which although they provide a sweet, calorie-free taste, they have often been accused of toxicity. This fact promotes the growing need for consumption of natural sweeteners, such as sweeteners from the plant Stevia rebaudiana Bertoni, which are 200-300 times sweeter than sugar and contain zero calories. The main objective of this work was to optimize the recovery of glycosides by dried stevia leaves. Dried samples were treated using green extraction techniques, namely ultrasound and microwave assisted extraction, using water as solvent, and extracts were compared with the conventional method. Several parameters, such as stevia / water ratio, time, temperature and power (microwave, ultrasound) were tested in order to optimize the glycoside recovery. The final extracts were evaluated for their total yield, antioxidant capacity and total phenolic content. The quantity and type of glycosides was also evaluated using HPLC. Based on the results, differences were observed between the extracts in terms of yield, antioxidant capacity and glycoside content. The optimum conditions were then used for the extraction of glycosides from samples that were dried and fertilized with different methods, to examine the effect of cultivation conditions on the quality and quantity of glycosides. Oven drying resulted in samples containing higher quantity of RebA and stevioside, while fertilization resulted in lower stevioside content.
Keywords: ultrasound and microwave assisted extraction, freeze drying, phenolics, antioxidant activity, RebA, stevi