Analysis Of The Chemical Constituents And Its Properties Of Stevia Rebaudiana

Stevioside, an abundant component of Stevia rebaudiana leaf, hasbecome well-known for its intense sweetness and is used as a non-caloricsweetener. This thesis mainly studies the stevioside from industrial extractionand separation, its chemical composition, the impurities, and the relationshipbetween steviosides' stucture and sweetness.Firstly, the extraction and separation process of stevia rebaudiana leafwas studied. Using the optimal extraction and separation process in industrialscale, we got the crude steviosides products. To identify the chemicalcomposition and impurities, Silica gel column chromatography,reversed-phase Sephadex LH-20, ODS-A and MCI-GEL chromatographywere used for a deep seperation, and finnally,12purified compounds wasobtained from the crude steviosides products. Identification of the purifiedcompounds by TLC, MS and NMR shows that the11compounds arerebaudioside A; rebaudioside B; rebaudioside M; stevioside;β-D-Glucopyranose,1-[(8R)-8-[(3,6-dideoxy-α-L-arabino-hexopyranosyl)oxy]nonanoate]; glucose;6-hydroxy-11-(β-D-glucopyranosyl)-2-cyclododecanone; 19-Nor-9-coprostene,3β-methoxy-3β-methy and the6-hydroxy-11-(β-D-glucopyranosyl)-2-cyclododecanone is a new compound.Secondly, the purified compounds' contents were detected by HPLC andthe HPLC conditions were optimized. The NH2-column and UV/ELSDdetecter were used for seperation and detection, and the mobile phase wasacetonitrile to water=4:1(v/v). Using external standard method forquantitative, the rebaudioside A's content was48.0%, the rebaudioside B'scontent was2.2%, stevioside's content was11.7%, and the glucose's contentwas30.8%. As some of the compounds were unsoluble or had a low content,the accurate quantification can not be carried out in this thesis.Finnally, the relationship between steviosides's stucture and sweetnesswere studies by computer simulation. As the results reported before, thesteviosides has8main structures, which was structure I,II,III,IV,V,VI,VII,VIII,and commonly, the steviosides in Stevia rebaudiana was classified intostructure V. Using sucrose as sweetness standard, whose sweetness value is1,structure I to VIII's sweetness value were500~1000,700~2500,100~2000,40~250,0~800, about100, about1000, about2400, respectively. Thecomputer simulation results proved that the sweetness increased with thedecrease of substituent's amount, which meant that the sterically indereddecreased the sweetness value and that the opatimal substituent's amount istwo. As the results showed, glucose is an indispensable part of these sugarsubstituent compounds, but the xylosyl compounds' sweetness value were slightly higher than rhamnosyl compounds'.