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Articles by T. Sun
Total Records ( 1 ) for T. Sun
  R. Letsididi , T. Sun , W. Mu , N.H. Kessy , O. Djakpo and B. Jiang
  The effects of different carbon, nitrogen and metal ion sources on the production of a β-cyclodextrin glycosyltransferase from a new alkalitolerant Bacillus licheniformis SK 13.002 strain were studied and effects of pH and temperature on the cyclization and hydrolysis activities assessed. Soluble starch was the best (0.131±0.003 U mL-1) carbon source while peptone combined with yeast extract (0.105±0.002 U mL-1) was an essential organic nitrogen source for enzyme production. MgSO4 (0.130±0.003 U mL-1) and FeCl2 (0.127±0.001 U mL-1) showed similar effect for CGTase production. Effect of FeCl2 on CGTase fermentation production has not been reported before. Glucose (0.0192±0.002 U mL-1) and maltose (0.0354±0.001 U mL-1) repressed enzyme production while CuSO4, ZnSO4 and ZnCl2 completely inhibited CGTase synthesis. The CGTase could significantly hydrolyze starch into short linear saccharides, with the hydrolysis activity exceeding cyclization activity four times. The enzyme showed an optimal cyclization activity (0.102±0.004 U mL-1) at pH 7.0 while optimal hydrolysis activity (0.461±0.003 U mL-1) was at pH 6.0. These activities were both optimal at 65°C. At 70 and 75°C, the relative cyclization activities were 87 and 50%, respectively, while those for hydrolysis were 98 and 93%, respectively. Therefore, B. licheniformis SK 13.002 CGTase has a potential for industrial application in processes where thermal activity is required. The hydrolytic activity of this CGTase is thought to be due to partial retention of ancestral enzyme function from evolution over time. However, this side reaction is undesirable since it produces short saccharides that are responsible for the breakdown of the cyclodextrins formed, thus limiting their yield.
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