Modulation of cyclizing activity and thermostability of cyclodextrin glucanotransferase and its application as an antistaling enzyme

Cyclodextrin glucanotransferase from Bacillus stearothermophilus ET1 (CGTase ET1) is a potential antistaling enzyme with cyclodextrin (CD)-forming activity. To reduce cyclization activity of CGTase ET1, phenylalanine residues at 191 and 255 were replaced with a glycine (F191G-CGTase ET1) and an isoleucine (F255I-CGTase ET1), respectively. Temperature optima of both mutant enzymes were lower than that of the wild-type. Cyclization activities of both mutants decreased dramatically, but F255I-CGTase ET1 showed a 2-fold higher hydrolytic activity than the wild-type enzyme. CD content of bread loaf treated with F191G-CGTase ET1 was 28.6% of that treated with wild-type, whereas no CD was detected in the loaf treated with F255I-CGTase ET1. Loaves treated with CGTase ET1 or either of the two mutants contained more of the larger maltooligosaccharides such as maltopentaose and maltohexaose than the control and the commercial antistaling enzyme-treated loaves. Retrogradation rates decreased significantly in the loaves treated with either mutant, which indicates the applicability of CGTase ET1 in the bread industry by modulating the cyclizing and hydrolyzing activities of the enzyme.