Pressurized Hot Water Extraction (PHWE) is a green and efficient technique for recovering bio-active molecules from natural materials using subcritical compressed liquid water in the temperature range of 50-150°C. The demand for natural substitutes of sugar for diabetics is increasing sharply. Stevia is one of such products available in the market which is extracted from stevia (Stevia rebaudiana) leaves. The two major sweet components (chemically known as glycosides) in stevia are stevioside and rebaudioside. The objective of this work is to study the effects of various parameters on the extraction of glycosides from stevia leaves using the PHWE technique. Experiments are conducted by varying different parameters, such as temperature (30-135°C), pressure (1-20 atm), extraction time (30-120 min), water to feed ratio (2-100 ml/gm), number of stages (1-3), stirring rate (0-350 rpm), and nature of feed pretreatment. The High-Performance Liquid Chromatography (HPLC) is used to identify steviosides and rebaudiosides in the extracted aqueous solution. The concentration of glycosides is measured using the colorimetric method namely, the phenol sulfuric acid method. The performance of the PHWE process has been evaluated by calculating the yield. The optimum condition is found at 120°C and 5 atm where the maximum total yield of 7.6% of glycosides is obtained in two consecutive extractions.
Palash Panja and Mamata Mukhopadhyay