Effect of peroxide oxidation on the expansion of potato starch foam

Abstract

Starch-based foams are drawing increasing interest as bio-sourced alternatives to petroleum-based products when a low-density or air-filled cell structure combined with reasonable mechanical resistance is required. The chemical modification of starch, mainly via oxidation, can improve its expansion capability and, thus, reduce the density of the resulting foam. This study was done to investigate how the oxidation of potato starch with different concentrations of hydrogen peroxide changes its chemical structure. This work provides new insights into how this impacts the paste foaming performance. The intrinsic viscosity of the starch solutions exhibited a linear decrease as the degree of oxidation increased, indicating that the molecular weight of the starch is reduced by oxidation because of chain scission. FTIR (and second derivative) analysis revealed the decrease in the number of C-H and C-O bonds caused by the conversion of CH2OH-6 into carboxyl groups in the oxidation reaction. In addition, NMR measurements showed a reduction in the signal assigned to the OH-6 hydroxyl groups, confirming their transformation into carboxyl groups. The densities of the foams prepared with the modified starches decreased as the oxidant concentration increased, from 308 kg/m(3) for native starch (NS) to 142 kg/m(3) for starch oxidized with 25% H2O2 (OS25). However, the starch prepared with the highest peroxide concentration showed a high density of 258 kg/m(3) (OS70). The dependence of the starch paste viscosity on the oxidant concentration, which results from a balance between the decrease in molecular weight and the increase in attractive chain interactions, was analyzed and an adequate interpretation for this behavior was provided. The internal bond strength of the foams exhibited the same trend as the density as a function of oxidant concentration (from 0.641 in NS to 0.439 in OS25) as expected because a lower density implies less mechanical cohesion within the foam.