猕猴桃果胶的黏度特性与流变性分析

采用冷冻干燥和热风干燥方法制备出猕猴桃果胶(kiwifruit pectin,KP),得到KP1和KP2两种成分,二者的pH值分别为3.16和3.39,主要含有半乳糖醛酸。以羧甲基纤维素钠(carboxy methyl cellulose-Na,CMC-Na)为参照系,采用MCR301旋转流变仪研究4因素(pH值、质量浓度、温度和剪切速率)对KP溶液流变性的影响。结果表明,KP1和KP2溶液黏度较低,在1.0 m Pa·s上下,溶液pH值和质量浓度对其影响有限。研究KP1和KP2溶液黏度与温度倒数1/T间的对数关系并观测到,10~30℃区间内其黏度随温度升高而下降,与CMC-Na溶液黏度变化相似。但40~50℃时其溶液黏度和流动性不完全遵循Arrhenius方程,究其原因,KP1和KP2活化能Ea分别为10.075 kJ/mol和4.510 kJ/mol,它们对温度的敏感性低,而导致其黏度和流动性发生改变。幂律方程对KP1和KP2溶液黏度和剪切速率的关系拟合,二者流动指数n均小于1,符合幂律定律对非牛顿流体特征的解释。因此,KP1和KP2溶液具有较典型的剪切稀化现象和流变性,可归属于非牛顿流体。但KP是一种低黏度果胶,故Arrhenius方程不能有效诠释KP溶液黏度与温度变化的规律。

Viscosity and Rheological Properties of Kiwifruit (Actinidia deliciosa) Pectin

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.