Studies On The Crystallization Process And Crystallization Thermodynamics Of Rebaudioside A

Stevia glycoside, a type of sugar source with development value and respected healthwhich is about200~350times sweeter than sucrose and only1/300calorific value of sucrose,is the high-saccharinity and low-calorie of natural sweetener. The major components of steviaglycoside are Stevioside and Rebaudioside A. Stevioside is300times sweeter than sugar andhas certain bitterness, while Rebaudioside A is450times sweeter than sugar and taste good,wnich is an ideal sweetener and widely used. Rebaudioside A is obtained mainly throughcrystallization, but the purity and yield need to be improved. This paper studied thecrystallization process of Rebaudioside A and used the Rebaudioside A crystallized to studythe properties of crystallization thermodynamics.Firstly, the ingredients of stevia glycoside raw material were determined, and thecrystallization solvents were also screened. Determination of composition of stevia glycosideshowed that the raw material was different from the ordinary stevia glycoside in this study.The stevia glycoside contained59.60%Rebaudioside A and25.80%Stevioside. Thepurification way of directly crystallizing Rebaudioside A was chosen. The methanol andethanol were selected as the alternative solvents.Secondly, the high purity of Rebaudioside A product was attained by means ofoptimization and combination of three kinds of crystallization process. The purity and yield ofRebaudioside A was improved. Three kinds of crystallization process and results were:(a) crystallization process by methanol: ration of material to solution1:4(w/w), watercontent in methanol10%(w/w), crystallization temperature5℃, crystallization time24h forprimary crystallization, ration of material to solution1:4(w/w) and water content in methanol25%(w/w) for the secondary crystallization, the purity of Rebaudioside A was97.1%and theyield was23.6%.(b) crystallization process by ethanol: ration of material to solution1:3(w/w), watercontent in ethanol2.5%(w/w), crystallization temperature5℃, crystallization time24h forprimary crystallization, ration of material to solution1:3(w/w) and water content in ethanol7.5%(w/w) for the secondary, ration of material to solution1:3(w/w), water content inethanol12.5%(w/w) for the tertiary crystallization, the purity of Rebaudioside A was98.7%and the yield was36.6%.(c) crystallization process by ethanol-methanol step-by-step: ration of material tosolution1:3(w/w), water content in ethanol2.5%(w/w), crystallization temperature5℃,crystallization time24h by ethanol for primary crystallization, and ration of material tosolution1:8(w/w), water content in methanol10%(w/w), crystallization temperature5℃,crystallization time24h by methanol for secondary crystallization, and the purity ofRebaudioside A was98.5%and the yield was38.1%. Compared with the crystallizationprocess by methanol or ethanol, the purity and yield of Rebaudioside A through crystallizationprocess by ethanol-methanol step-by-step was higher, and it was also improved compared tothe crystallization process in the industrial production Thirdly, the properties of crystallization thermodynamics of Rebaudioside A wereexplored. The results indicated that the solubility of Rebaudioside A elevated with theincrease of temperature and water content in methanol or ethanol. The metastable zone widthwere3.2~6.6℃and3.0~4.8℃in75%(w/w) methanol and92.5%(w/w) ethanol. The higherthe saturation temperature was, the narrower the metastable zone width was. The metastablezone width widened with the increase of cooling rate, while firstly decreased and thenincreased with the increase of agitating rate. According to the metastable zone width in75%methanol, the99.3%Rebaudioside A was obtained, while the same material crystallized insupersaturated area and the97.5%Rebaudioside A was obtained.Lastly, the quality indexes of Rebaudioside A obtained by means of crystallizationprocess were determinated. Determination of the quality indexes of Rebaudioside A andcompared with marketed products pointed that the purity of Rebaudioside A productcrystallized was higher. The melting point, the pH of1%(w/v) solvent, the absorbance, thespecific rotation and the residual solvent all met the requirements. The results showed that thequality of Rebaudioside A crystallized was better.