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

Branched alpha-dextrins with different molecular weights were prepared fi om waxy maize. A series of beta-limit dextrins was prepared from alpha-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 alpha- and beta-limit dextrins and commercial potato amylose were determined by gel-permeation chromatography (GPC) and with a dual light-scattering detector Solubilized potato amylose and alpha- and beta-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 alpha-dextrin and on the molecular weight of alpha-dextrin. alpha-Dextrin caused an increase of storage modulus, G, when the amylose: alpha-dextrin ratio was low and the molecular weight of alpha-dextrin was high. The high-molecular-weight alpha-dextrin influenced amylose gelation in the same way as native waxy maize starch, but the medium-and low-molecular-weight alpha-dextrans weakened the gel formation, especially at a ratio of 25:75 (amylose, alpha-dextrin). When low-molecular-weight beta-limit dextrins were mixed with amylose, the resulting gels were more rigid than those in which amylose was mixed with corresponding alpha-dextrins. When high-molecular-weight beta-limit dextrins were mixed with amylose, the resulting gels were weaker.