Modification of Rice Starch by Selective Degradation of Amylose Using Alkalophilic Bacillus Cyclomaltodextrinase

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• 作者：Joong-Hyuck Auh ; Hye Young Chae ; Yong-Ro Kim ; Kyu-Ho Shim ; Sang-Ho Yoo ; and Kwan-Hwa Park
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2006
• 出版时间：March 22, 2006
• 年：2006
• 卷：54
• 期：6
• 页码：2314 - 2319
• 全文大小：250K
• 年卷期：v.54,no.6(March 22, 2006)
• ISSN：1520-5118

文摘

A cyclomaltodextrinase (CDase) isolated from alkalophilic Bacillus sp. I-5 (CDase I-5) exists in adodecameric form, an assembly of six dimers, each catalytic site of which is located in a narrowgroove at the interface of the dimeric unit. Because of the unique geometric shape of the catalyticsite, the enzyme has the ability to discriminate the molecular size of substrates. An analysis of thehydrolysis reaction of the enzyme revealed that its k_cat/K_m 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 towardamylose. CDase I-5 was applied to modify the starch structure to produce low-amylose starch productsby incubating rice starch with this enzyme. We found that the amylose content of rice starch decreasedfrom 28.5 to 9%, while the amylopectin content remained almost constant with no significant changein the side chain length distribution. When the CDase I-5-treated rice starch was stored at 4 C for7 days, the retrogradation rate was significantly retarded as compared to that in the control sample.Keywords: Alkalophilic Bacillus I-5; cyclomaltodextrinase (cDase); low-amylose starch; retrogradation