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

Maize starches with different amylose content were investigated by differen tial scanning calorimetry (DSC) and X-ray diffraction (XRD). It was shown t hat the differences in amylose content in maize starches resulted in change s in the structural and thermodynamic properties. The melting process of wa xy and normal maize starches could be described by means of a "two-state" m odel. The melting process of the maize starches, which contained at least 5 0% (w/w) amylose, were described as the melting of a mixture of low and hig h 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 cal orimetric peaks. The values of the melting co-operative units (nu) and the thickness of crys talline 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- a nd B-type crystals were calculated as 4.8 +/- 0.6 and 10.7 +/- 1.8 nm, resp ectively. (C) 2001 Elsevier Science Ltd. All rights reserved.