MICROSTRUCTURE OF AMYLOSE GELS

The aim of this investigation was to study the structural characteristics of amylose gels (2-8% w/v) at different scales of organization. Native gels have been studied by electron microscopy, mild acid hydrolysis, differential scanning calorimetry and size-exclusion chromatography. A model for organization of the polysaccharide within the gel structure is proposed. Amylose gels exhibited a macroporous structure (mesh size 100-1000 nm) containing filaments 20 +/- 10 nm wide. The filaments resulted from the association of segments of amylose chains (26 < DP(n) < 31; 56 < DP(w) < 73) which were orientated obliquely to the filament axis. These amylose fragments were partially organized in a B-type crystalline array. Amylose gels also contained an amorphous fraction consisting of 18-33% of the polysaccharide. This fraction was easily degraded by acid hydrolysis. The amorphous fraction was described as dangling chains (6 < DP < 30) located in the macroporous structure. It was mainly responsible for the hydrodynamic behaviour and the porosity of native amylose gels. The limit between the associated and amorphous regions of the gel was not perfectly defined and an intermediate zone which may recrystallize upon acid hydrolysis was identified.