Rheological modeling of non-depectinized beetroot juice concentrates

Abstract

The rheological behavior of non-depectinized beetroot juice concentrate (25, 35, 45 and 55 °Brix) was studied over a wide range of temperature (30, 40, 50, 60, 70 and 80 °C) using a controlled rate, rotational rheometer. From the applied non-Newtonian rheological models, power law model was found to be the best fit with the values of flow behavior index (n) ranging from 0.6182 to 0.9962 showing the shear-thinning nature of beetroot juice concentrate (n < 1). The apparent viscosity was greatly affected by the increased soluble solids’ content at lower temperatures. Activation energy (E _a ) calculated for each concentrated sample was observed to ascend from 14.8 to 25.03 kJ·mol⁻¹ with increase in juice concentration. The exponential model suitably explains the dependency of consistency coefficient (K) on concentration at different temperatures. Combined effect of temperature and concentration on ‘K’ was also examined and conclusively the exponential model was fitted well and a single equation was derived.

$$ K\, = \,5.59\, \times \,10^{ - 6} \,\exp \,\left( {0.08\,C\, + \,\frac{2652.5}{T}} \right),\quad \quad \left( {{\text{R}}^{2} = 0.996{\text{ and RMSE}} = 0.0004} \right) $$

where, K is the consistency coefficient (Pa.sⁿ), C is the total soluble solid content in °Brix and T is the temperature in °K.