The influence of O-formylation on the scale of starch macromolecules association in DMSO and water

There is a great challenge in finding treatments that may degrade the initial grain structure of native starch in order to get better mixing properties of the resulting degradation product with other polymers. Among the possible treatments, O-formylation has already been proposed but only little structural information on the resulting degradation products is available, certainly due to its heterogeneity. The present study aims to complement our knowledge on the structure of macromolecules following the chemical reaction by means of different techniques. At first, polarimetry reveals, on amylose and maltodextrin samples, that the helix content remains unchanged after esterification. Then, high resolution 1H NMR measurements allow to determine the association parameter, p, and it was found that the fraction of associated helix, although strongly influenced by the nature of the solvent, is similar for native and starch formate. It was deduced that formic acid is not reactive on the less accessible macromolecules such as the aggregates preserved from the initial destructuration of starch during gelanitisation and following the thermal treatment, i.e. the larger molar weight samples. Finally, AFM observation corresponded well with the results obtained by the other techniques, since large aggregates, such as helix assemblies or amorphous and globular aggregates, were found to be unaffected by the formic acid treatment.