| Stevioside is a natural sweetener isolated from Stevia RebaudianaBertoni. It's uses are restricted due to inherent bitterness and astringency. Howto overcome the disadvantages is becoming the focus of study. This study projectmainly discussed the synthesis of alpha-glucosyl stevioside in order to improvethe quality of taste by the action of CGTase (cyclodextrin glucosyltransferase)and its uses in dairy product.1 The best strain bacillus spore M-9 for producing CGTase was selected fromthree strains. Its fermentation characteristics were investigated. The formulaof culture medium was optimized as: soluble starch 2. 0%, MgSO4·7H2O 0. 02%, K2HPO40. 1%, yeast extraction 0. 5% and peptone 1. 0%. The optimum conditions were: pH=9. 5temperature 33℃, capacity 75m1/250ml triangular bottle and time 80hrs.2 Properties of CGTase were investigated. The enzyme exhibited an optimumtemperature of 55℃ and an optimum pH at 5. 5, The activity of the enzyme waslightly increased by addtion of Mg2+, but was strongly inhibited by Fe2+ and Mn2+and evidently inhibited by Cu2+ and Zn2-.3 The reaction conditions for production of alpha-glycosyl steviosides byCGTase were detailedly studied. The effect of pH and the ratio of stevioside tostarch on transformation rate were studied above all, the transformation ratewas significantly affected by the ratio of soluble starch to stevioside, but pHhas little influence on reaction. Based on the results of analysis, the quadraticrotary combination design was used to study the procedure of transformation rateof stevioside between 7075%. As pH was 5. 0 and the ratio of soluble starch tostevioside was 1: 3, the optimum conditions of reaction were gained:temperature38. 3149. 9℃, the amount of enzyme 51. 61～62. 3U/g soluble starch, time26. 8～42. 8hrs. The recovery of product was 110%.4 Alpha-glycosyl stevioside was identified by glucoamylase. The resultssuggested that the product synthesized from stevioside by CGTase wasalpha-glycosyl stevioside.5 The quality of taste of product was evaluated. The results suggested thatthe mixture of the glucosylated product hasn't bitterness and astringency, thesveetness to sucrose(=1) was 90.6 The uti1ization of product in dairy product 'as studied first1y. The resultsuggested that the transformation product can be used in yogUrt and beverage tosubstitute sucrose. the substituted anount separately was 6on in yogurt and 40%in fermented dairy beverage. |
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