Correlation between transient rotational viscometry and a dynamic oscillatory test for viscoelastic starch based systems

Gelatinized starch formulations including lipids and xanthan gum, typical of viscoelastic foodstuffs, were analyzed using a rotational viscometer (transient conditions) and an oscillatory rheometer. Ultra-rapid and slow freezing processing conditions, which can modify product stability, were also tested. Transient shear stress curves showed a typical overshoot and a structural breakdown; the Bird-Leider model satisfactorily fitted these curves. Model parameters were correlated with characteristic peak stress (sigma(max), peak time (t(max)) and relative overshoot corresponding to the a vs time curve. Relationships between transient shear stress data and dynamic measurements (G', G*, delta) for viscoelastic ranges were found for the starch-based systems and were used to assign a physical meaning to Bird-Leider parameters. Viscoelastic starch systems were grouped in different zones of the correlation diagrams based on structure properties like rigidity, stability to the applied strain and fluid characteristics after breakdown.