Obtainment of sweet compounds from stevia (Stevia rebaudiana) plant by decanter extraction method

The aim of this research is to determine the availability of decanter extraction that can be a fast and affordable method for isolation steviol glycosides from stevia leaves. Usage of water as the extraction solvent in this study instead of organic solvents used in patented methods, has enabled the process to be economical in addition to be an environmentalist approach. In order to enrich steviosides from aqueous extracts, ultrafiltration membrane filters different in cut-off size were used except from conventional physical separation techniques. Steviol glycosides are extracted from stevia leaves by using batch system with ethanol as solvent, generally. In this research decanter extraction system with water as solvent in the extraction of steviol glycosides was experienced first time. In the first stage of the study, Response Surface Methodology was used to optimize decanter extraction parameters such as temperature, time, plant/water ratio and decanter speed. The optimal combination that was determined as a result of optimization studies was 25 °C temperature, 1/27.6 plant/water ratio, 105 minutes extraction time and 5280 rpm decanter speed. In the next stage, ultrafiltration of enzyme and adsorbent applied examples were performed by using filters having 4 different membrane cut-off rates as 50, 30, 10 and 5 kDa. The results from this study showed that PVPP application enhanced the purity level of extract in terms of stevioside and rebaudioside A. Effect of ultrafiltration on concentration of target steviol glycosides was found significant, statistically. Sample, which was highest in purity of stevioside and rebaudioside A, was obtained by ultrafiltration with membrane having 30 kDa cut-off rate after laccase and 2 % PVPP treatments. Purity levels of this sample in terms of stevioside and rebaudioside A were determined as 26.39 % and 19.80 %, respectively. Total phenolic compounds content and total antioxidant capacity of this sample were determined as 187.51 mg GAE/L and 117.42 TE/L. A significant reduction has occurred in amount of total phenolic compounds and antioxidant capacity of samples that were treated with laccase and PVPP compared to control. Transmittance values of samples were enhanced with decreasing cut-off rate up to 5 kDa by ultrafiltration process. L value, expressing lightness-darkness level of extract colour, showed increament after the ultrafiltration. a value representing redness was higher in laccase applied samples, while b value indicating yellowness was higher in PVPP applied samples.