Rheological behaviour of fresh and frozen potato puree in steady and dynamic shear at different temperatures

Rheological behaviour of natural and commercial potato purees was studied in steady and dynamic shear conditions at sample temperatures ranging from 25–65 °C. Both types of puree were frozen-then-thawed to determine how changes occurring in their structure affected their rheological behaviour. All of the purees presented shear-thinning behaviour with yield stress. Dynamic shear data revealed weak gel-like behaviour in the purees: magnitudes of G′ were higher than those of G″, and both increased with frequency. For fresh natural puree and fresh and frozen/thawed commercial puree, the frequency dependence of G′ increased, and the frequency dependence of G″ decreased with sample temperature. Processing weakened the structure of natural puree but resulted in a coarsely aggregated structure in commercial puree. The effect of sample temperature on dynamic parameters was more significant in processed than in fresh purees. The Cox-Merz rule was not applicable to the steady and dynamic shear data on all of the purees. For fresh natural puree, the two types of data conformed to the use of shift factor on frequency, and therefore for this product it would be possible to estimate steady shear data from dynamic shear data, and vice versa. For fresh commercial puree, the relationship between steady and dynamic shear data was non-linear. In both processed purees, the linearity or otherwise of the relationship between viscosities was dependent on sample temperature.