INFLUENCE OF AMYLOSE AMYLOPECTIN RATIO ON GEL PROPERTIES

The aim of this work was to study the structural features of aqueous starch gels as a function of their amylose:amylopectin ratio, r. Structural characteristics of amylose-amylopectin gels were studied using uniaxial compression measurements, mild acid hydrolysis, α-amylolysis, X-ray diffractometry and hot water solubility. Two families of gels were isolated according to the amylose:amylopectin ratio (r). Mixed gels had similar behaviour either to pure amylopectin gels for r < 0·43 or to pure amylose gel for higher values of r. Amylopectin-rich gels were fairly well degraded both chemically (60 to 100%) and enzymically (∼ 50%), but had poor mechanical properties and solubility behaviour. Amylose-rich gels however were slightly degraded (∼ 20% in all cases), but exhibited good mechanical and thermal resistances. Results were explained in terms of supra-molecular organization, suggesting a phase-separated structure with a continuous matrix of one polymer embedding microdomains of the second polymer. Polymer composition of each phase was determined by the ratio r, and the particular value of r = 0·43 was interpreted as the inversion point between the two types of gel. © 1991, Academic Press Limited. All rights reserved.