Thermal and viscoelastic properties of starch isolated from mexican corn hybrids

The aim of this work was to characterize the thermal (gelatinization temperature and melting enthalpy of retrograded starch) and rheological (viscoelasticity and viscosity in Bravebder Units) properties of starch isolated from different corn hybrids grown in Mexico. The gelatinization temperatures of the starches ranged from 71.5 to 74.7 °C. Melting temperatures of the retrograded starches were lower than the gelatinization temperature at the 7th and 14th day of storage, while the melting enthalpies of retrograded samples were usually higher only after 14 days. The rheological profiles showed that pastes formed during the first two stages (heating-cooking) of a heating/cooling kinetics, behaved as "weak" viscoelastic gels, with greater elastic modulus than viscous modulus (G′>G″). However, at the third (cooling) stage, all starch samples showed the behavior of "elastic" gels (G′>G″). Viscoamylograms showed that 5 (w/v) % total solids starch pastes reached peak viscosity at about 93 °C, whereas for 10 (w/v) % total solids pastes the peak was registered at about 87 °C . According to the statistical analysis, there were significant differences among starches regarding their chemical features, as well as their thermal and rheological properties. In view of their high tendency to retrograde and their "weak" gel viscoelastic properties during processing, the starches may have applications in non-processed foods.