Modelling and Optimization of Subcritical Water Extraction of Rebaudioside A and Stevioside from Stevia Rebaudiana Leaves in Southeastern Mexico

The extraction of the sweetening ingredients from Stevia leaves has been performed using conventional techniques, which are not sustainable from an environmental point of view. Lately, some innovative methods known as “green extractions” have been developed, using fluids under subcritical and supercritical conditions. The objective of this work was modelling and optimization of extraction of the sweetening glycosides rebaudioside A and stevioside from leaves of Stevia rebaudiana B. Morita II variety, using water in subcritical conditions as the extraction agent, to maximize yield. The experiment was conducted following a 23 factorial design with 5 central points, considering a first-order polynomial model and factors such as temperature (100–150ºC), time (30–90 min), and the Stevia leaf/water ratio (1:10 and 1:20 m/v). The overall yield of extracted glycosides (g dry extract/100 g leaf) and rebaudioside A and stevioside levels were evaluated as response variables. Analysis of variance indicated that the stevia leaf/water ratio factor and the temperature-time interaction presented a significant influence (p < 0.05) on the yield of glycoside extraction, but time didn’t significantly (p < 0.05) affect the overall extraction. The best treatment consisted of pressurized water (300 bar) at 150 ºC temperature for 30 min and a stevia/water ratio of 1:20 m/v. Under these conditions, an overall yield of 57.67% of dry extract was obtained, with yields of 41.41% of rebaudioside A and 6.77% of stevioside. The extracts of S. rebaudiana leaves obtained may serve as a source of sweeteners in the food industry to prepare healthy foods with low caloric density.