Viscoelastic properties of sweet potato puree infant food

Dynamic mechanical spectroscopy and steady-shear theological 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 degrees 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 (eta*) and apparent viscosity (eta) decreased with temperature between 5 and 50 degrees C. A modified Cox-Merz rule with a shift factor resulted in superimposition of steady and dynamic shear viscosity data. A deviation in theological behavior at and above 65 degrees 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 degrees C). (c) 2005 Elsevier Ltd. All rights reserved.