Cereal Chem. 73 (4):428-432  |  VIEW ARTICLE

Enzymes

Susceptibility of Amylose-Lipid Complexes to Hydrolysis by Glucoamylase from Rhizopus niveus.

Kanefumi Kitahara (1), Toshihiko Suganuma, and Tomonori Nagahama. (1) Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima University, 21-24 Korimoto 1-chome, Kagoshima 890, Japan. E-mail: <kitahara@chem.agri.kagoshima-u.ac.jp> Accepted March 14, 1996. Copyright 1996 by the American Association of Cereal Chemists, Inc. 

The amylose-lipid complexes were prepared from potato amylose with fatty acids (FA) and lysophosphatidylcholine (LPC), and their susceptibilities to hydrolysis by glucoamylase (Rhizopus niveus) were examined. The prepared complexes had the respective amount of lipid in them, depending on the sort of lipid (0.91-2.93 µmol/10 mg of amylose), and showed no typical peaks of the crystallized V-form on X-ray diffractograms. The complexes showed the extent of hydrolysis ranging from 4.8% for LPC to 22.0% for linolenic acid by 83.4 nkat of the enzyme for 72 hr, which was lower than the hydrolytic extents of cereal starches. When the complexes in excess water were treated by heating at not more than the respective melting temperature for 2 hr, no change in the X-ray diffractogram was observed, but the extent of hydrolysis was decreased to 3.2-16.5%. During the hydrolysis of the heat-treated complexes, it was found that the complexed lipids were hardly released from them, except for unsaturated FA. Also, the ability of adsorption of the glucoamylase on the complex was determined. It was found that the residues after glucoamylase hydrolysis, glucoamylase-resistant complex, showed decreased ability of enzyme adsorption compared with the intact complex. These results indicate the complex-forming portion itself is strongly resistant to the action of glucoamylase.