The relationship between thermodynamic and structural properties of low and high amylose maize starches

Maize starches with different amylose content were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). It was shown that the differences in amylose content in maize starches resulted in changes in the structural and thermodynamic properties. The melting process of waxy and normal maize starches could be described by means of a "two-state" model. The melting process of the maize starches, which contained at least 50% (w/w) amylose, were described as the melting of a mixture of low and high temperature populations of double-helical type crystallites, denoted as B- and B*-type, as well as the melting of V-type crystallites. The relative amounts of the three structures were determined by deconvolution of the calorimetric peaks. The values of the melting co-operative units (nu) and the thickness of crystalline lamellae (pitch heights) for low (waxy and normal) and high amylose starches were determined using a mathematical model describing the melting process. The nu in A- and B-type crystals were calculated as 13.7 +/- 1.7 and 30.6 +/- 5.0 glucose units, respectively. The pitch heights of the A- and B-type crystals were calculated as 4.8 +/- 0.6 and 10.7 +/- 1.8 nm, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.