Modification of rice starch by selective degradation of amylose using alkalophilic Bacillus cyclomaltodextrinase.
A cyclomaltodextrinase (CDase) isolated from alkalophilic Bacillus sp. I-5 (CDase I-5) exists in a dodecameric form, an assembly of six dimers, each catalytic site of which is located in a narrow groove at the interface of the dimeric unit. Because of the unique geometric shape of the catalytic site, the enzyme has the ability to discriminate the molecular size of substrates. An analysis of the hydrolysis reaction of the enzyme revealed that its kcat/Km value on amylose was 14.6 s(-1) (mg/mL)(-1), whereas that for amylopectin was 0.92 s(-1) (mg/mL)(-1), showing an exceptionally high preference toward amylose. CDase I-5 was applied to modify the starch structure to produce low-amylose starch products by incubating rice starch with this enzyme. We found that the amylose content of rice starch decreased from 28.5 to 9%, while the amylopectin content remained almost constant with no significant change in the side chain length distribution. When the CDase I-5-treated rice starch was stored at 4 degrees C for 7 days, the retrogradation rate was significantly retarded as compared to that in the control sample.
Auh
Joong-Hyuck
JH
Center for Agricultural Biomaterials and Department of Food Science and Biotechnology, School of Agricultural Biotechnology, Seoul National University, Seoul 151-742, Korea.
Chae
Hye Young
HY
Kim
Yong-Ro
YR
Shim
Kyu-Ho
KH
Yoo
Sang-Ho
SH
Park
Kwan-Hwa
KH
D000687:Amylopectin / Q000378:metabolism; D000688:Amylose / Q000378:metabolism*; D001407:Bacillus / Q000201:enzymology*; D002850:Chromatography, Gel; D002855:Chromatography, Thin Layer; D006026:Glycoside Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012275:Oryza / Q000737:chemistry*; D013213:Starch / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature
D013213:Starch; D000688:Amylose; D000687:Amylopectin; D006026:Glycoside Hydrolases; C048745:cyclomaltodextrinase