Transglycosylation Of Stevioside By Cyclodextrin Glucanotransferase And The Study On Its Bioactivities

Stevioside is a low-calorie natural sweetener at high magnificent, but the after bitter tastelimits its application. In this paper, the transglycosylation of stevioside to improve theedulcorant quality was investigated by using free cyclodextrin glucanotransferase andimmobilized cyclodextrin glucanotransferase. In addition, the microwave assistedtransglycosylation of stevioside using CGTase were investigated, respectively. Finally, thebio-activities of the stevioside derivatives were studied. The main contents and results are asfollows:1The glycosyl donors affected the transglycosylation reaction. The results showed that theconversion of stevioside reached the highest with β-cyclodextrin. Moreover, theconversion rate gradually increased with the extension of reaction time and reachedequiblium at8hour. With controlled parameters, the highest stevioside conversionreached87.8%with β-cyclodextrin as glycosyl donors under the condition of60oC, moleratio of1.06:1,5%substrate concentration and catalyzed by10U CGTase/g stevioside inwater for3hours. However, the conversion of stevioside was59.9%with cornstarchhydrolyzate.2The cyclodextrin glycosyltransferase was immobilized on chitosan via cross-link byglutaraldehyde. The results showed that the high activity recovery of94.5%ofimmobilized enzyme could be achieved at25oC,0.02g/mL chitosan,4%(v/v) ofglutaraldehyde,10UCGTase,1h cross-link and15h immobilization. In thetransglycosylation of stevioside, the optimum reaction temperature of the immobilizedenzyme increased5oC, the optimum pH was the same as the native enzyme. Meanwhile,the conversion of stevioside enhanced5%-8%at any other pH assayed, and the thermalstability enhanced10%at5hour.3The stevioside derivatives were synthesized by chemical method and the microwave wasused to the transglycosylation of stevioside by CGTase. The microwave accelerated thereaction rate in the transglycosylation of stevioside by CGTase compared with theconventional heating method. The conversion of stevioside attained50.5%under thefollowing optimal conditions of50W,55oC,1.5:1substrate mass ratio,1min,10UCGTase/g stevioside. Meanwhile, the transglycosylation of stevioside only can be reactedusing glucose as glycosyl donor catalyzed by aluminium chloride in the chemicalsynthesis reaction. Comparing to the reaction in aqueous solution, the conversion ofstevioside enhanced20%in ethanol solution. Moreover, the boric acid adding to theenzyme reaction can make contribution to enhancing the conversion of stevioside.However, there were no detective products after adding the aluminium chloride to theenzyme reaction. Finally, some organic solvent can decrease the conversion of stevioside.4The bio-activities of stevioside and the stevioside transglycosylation products which werecatalyzed by3different cyclodextrin glucanotransferase were studied. The research wasabout the scavenging activity of1-1-diphenyl2-picryl hydrazyl and the hydroxyl radical.Meanwhile, the inhibition of tyrosinase activity and anti-lipid peroxidation activity were investigated. The results indicated that they all have some certain bio-activities. Theproducts catalyzed by cyclodextrin glucanotransferase (Paenibacillus macerans JFB05-0)revealed the best bio-activities.