Abstract
The rheological behaviour of date-water concentrates of three date cultivars has been determined using a Haake VT 181 concentric-cylinder rotational viscometer. The date cultivars used were Khudary, Sufri, and Serri; and the date-water concentrates were 20, 30, 40, 50, 60, and 70 °Brix. The 20 and 30 °Brix concentrates exhibited Newtonian flow in the temperature range 25–85 °C while the other concentrates (40, 50, 60 and 70 °Brix) were well described by the simple power law model in the temperature range 25–95 °C and their flow was non-Newtonian exhibiting pseudoplastic behaviour. Temperature had a pronounced effect on consistency coefficient of samples at 40 °Brix concentrations from the three cultivars. The magnitude of the consistency coefficient decreased with increase in temperature. The Arrhenius model described the effect of temperature on the apparent viscosity with activation energies from 1.9 × 10
4 to 3.1 × 10
4 kJ kg
−1 mol
−1 at 50 s
−1, from 1.9 × 10
4 to 3.2 × 10
4 kJ kg
−1 mol
−1 at 100 s
−1, and from 1.9 × 10
4 to 3.3 × 10
4 kJ kg
−1 mol
−1 at 200 s
−1. The magnitude of activation energy increased with increase in concentration.