Effect of centrifugal force on the diffusion of steviol glycosides in Stevia extraction

Sweeteners are artificial or natural substances produced to replace sugars used in daily life, usually sweeter than the same amount of sugar and contain less energy. High consumption of many sweeteners causes some adverse health effects. Therefore, alternative sources were needed. In recent years, the tendency to use natural sweeteners as an alternative to artificial sweeteners and sugar alcohols has been increasing in the production of foodstuffs. It is thought that natural sweeteners produced from the stevia plant (Stevia rebaudiana B.), which is considered "green gold" in many developed countries and known as sugar grass, can be used in the prevention of chronic diseases such as diabetes and obesity. Steviol glycosides are 200-300 times sweeter than sucrose, and although no adverse effects on human health have been proven, their caloric value is considered zero (0). In addition, the stevia plant also has bioactive antioxidants such as phenolic compounds that have positive health effects apart from steviol glycosides. Various purification steps follow the extraction step of steviol glycosides in industrial production. Traditional methods are used to isolate compounds with the nutritional value from plant sources. For this, many analytical methods are suggested in the literature. Some of these methods can be listed as supercritical liquid extraction (SFE), Subcritical water extraction (SCW), ultrasound applications, microwave applications, ultrafiltration, and high-pressure liquid extraction (HPLE) using CO2 and ethanol as co-solvent. However, the need to obtain sustainable and viable processes, which are now known as eco-friendly, has led both food industries and food scientists to develop new processes that are fully compatible with the concept of green extraction. For this purpose, there are many ongoing studies on the extraction of steviol glycosides and their use in the production of sweetened products. Recently, new environmentally sound approaches have been investigated for the extraction of steviol glycosides (SGs). These are, for example, pressurized hot water (PHWE), microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), and high-performance Thin-layer chromatography (HPTLC). In this research, studies were carried out to determine the effect of various process conditions for the extraction of major steviol glycosides from stevia leaves. Experiments were made using three extraction parameters. These factors are; dilution factor, extraction temperature, and centrifugal force were chosen. Water was used as a solvent in the first experiment, and fresh stevia leaf was used as a material. Centrifugal force was applied at 2400, 2900, and 3400xG levels for centrifugation. The extraction temperature was chosen as 40, 45, and 50°C, and the dilution factors were set as 5 fold, 7,5 fold, and 10 fold. In the second experiment, water as a solvent and dried stevia leaves were used as material. In the third experiment, the study was carried out in previous conditions using ethyl alcohol as a solvent and dried stevia leaf as material. In all trials, sampling conditions were optimized using the surface response method and considering five responses. In order to isolate the highest amount of rebaudioside A from stevia extracts, the optimum conditions predicted by the Box-Behnken Design (BBT) method were established. Accordingly, a dilution factor of 7,69 times, a centrifugal force of 2915xG, and an extraction temperature of 44,77°C were applied. In addition, 8,44 dilution factor, 3399,99xG centrifugal force, and 40°C extraction temperature were applied to the aqueous extracts of the dried stevia leaf to extract maximum rebaudioside A and stevioside yield. It was determined that 3002.36xG centrifugal force and 40°C extraction temperature were suitable for maximum rebaudioside A and stevioside extraction from ethanolic extracts. The highest steviol glycoside yield was achieved in extraction experiments using water as solvent.