Abstract: Kiwifruit pectin (KP), named as KP1 and KP2, were prepared by hot-air drying and freeze drying, respectively, the pH of which were 3.16 and 3.39 and both of which contained mainly D-galacturonic acid (D-GA). Using carboxy methyl cellulose-Na (CMC-Na) as control, the effects of four factors including pH, pectin concentration, temperature and shear rate on rheological properties of KP solution were explored by MCR301 rotary rheometer. The results showed the viscosity of both KP1 and KP2 solutions was low, approximately 1.0 mPa·s, and it was little impacted by pH and KP concentration. The observed logarithmic relationship between pectin viscosity (lnη) and reciprocal temperature (1/T) indicated that the viscosity of both pectin solutions went down with the increase in temperature in the range of 10–30 ℃, similar to CMC-Na. However, the viscosity and fluidity of KP1 and KP2 solutions failed to completely follow the Arrhenius equation in the range of 40–50 ℃, which may be due to the lower activation energy (Ea) of 10.075 kJ/mol for KP1 and 4.510 kJ/mol for KP2, and consequently lower temperature sensitivity. The relationship between viscosity and shear rate for the pectin solutions was fitted with a power law equation. Both flow indexes n were less than 1. The non-Newtonian fluid properties of KP1 and KP2 could be explained by the Power Law equation. Therefore, both of them exhibited a typical shear thinning phenomenon and ductility, which can be attributed to non-Newtonian fluid. But KP was a low viscosity pectin, so the Arrhenius equation could not effectively explain the relationship of its viscosity and temperature.

Key words: viscosity, shear thinning, rheology, power law, kiwifruit pectin