Viscoelastic properties of sweet potato puree infant food

Dynamic mechanical spectroscopy and steady-shear rheological tests were carried out to evaluate viscoelastic properties of commercial sweet potato puree infant food using a controlled stress rheometer. The puree behaved like an elastic solid with G′ predominating over G″(G′ > G″). Both elastic and viscous moduli decreased with an increase in temperature while an abnormal increase in G′ was noticed at 65 °C. Steady shear viscometry, covering the shear rate range 0.1 to 100 s−1, generally indicated the presence of yield stress and good fit of data by the Herschel–Bulkley model. The complex shear viscosity (η*) and apparent viscosity (η) decreased with temperature between 5 and 50 °C. A modified Cox–Merz rule with a shift factor resulted in superimposition of steady and dynamic shear viscosity data. A deviation in rheological behavior at and above 65 °C was likely caused by gelatinization and possible amylase–lipid complex formation of sweet potato starch as confirmed by two distinct DSC thermal transitions peaks (57 and 94.5 °C).