Effects of enzymically modified amylopectin on the rheological properties of amylose-amylopectin mixed gels

Abstract

Branched α-dextrins with different molecular weights were prepared from waxy maize. A series of β-limit dextrins was prepared from α-dextrins and native amylopectin. The fine structure of the dextrin samples was investigated by debranching, and was found to be similar to the unit chain distribution of native amylopectin. The absolute molecular weights of α- and β-limit dextrins and commercial potato amy lose were determined by gel-permeation chromatography (GPC) and with a dual light-scattering detector. Solubilized potato amy lose and α- and β-limit dextrins were mixed at different ratios to give a total concentration of 8%. Dynamic viscoelastic measurements showed that gel formation of amylose was highly dependent both on the ratio of amylose to α-dextrin and on the molecular weight of α-dextrin. α-Dextrin caused an increase of storage modulus, G, when the amylose: α-dextrin ratio was low and the molecular weight of α-dextrin was high. The high-molecular-weight α-dextrin influenced amylose gelation in the same way as native waxy maize starch, but the medium- and low-molecular-weight α-dextrins weakened the gel formation, especially at a ratio of 25:75 (amylose: α-dextrin). When low-molecular-weight β-limit dextrins were mixed with amylose, the resulting gels were more rigid than those in which amylose was mixed with corresponding α-dextrins. When high-molecular-weight β-limit dextrins were mixed with amylose, the resulting gels were weaker.