微波降解果胶对其流变性质的影响及动力学

对不同质量浓度(0.5、1.0、1.5、2.0 g/100 m L)的果胶溶液微波处理不同时间(0、1、3、5、8、15、20、30 min)后的流变性质及动力学进行考察。结果表明,随着果胶溶液质量浓度降低、微波处理时间延长、剪切速率增大,样品的表观黏度和特性黏度η]均降低。用牛顿幂律方程描述溶液的流体行为,果胶溶液是剪切稀化的假塑性非牛顿流体,在低质量浓度时,微波处理对溶液的流体行为影响最大。根据特性黏度对样品进行反应动力学拟合,发现果胶的微波降解遵循反应一级动力学,在质量浓度0.5 g/100 m L时降解速率最快,质量浓度1.5 g/100 m L时降解速率最慢。经与沸水浴无微波的空白组对比,发现微波降解果胶的过程还存在非热效应。

Effect of Microwave Treatment on Rheological Properties and Degradation Kinetics of Pectin

The rheological properties and degradation kinetics of pectin at various concentrations (0.5, 1.0, 1.5 and 2.0 g/100 mL) subjected to microwave treatments for different time periods (0, 1, 3, 5, 8, 15, 20 and 30 min) were assayed. The results showed that both the apparent viscosity and intrinsic viscosity η] of the samples decreased with the reduction of pectin concentration, and with the increase of microwave processing time and shear rate. Using power law equation to describe their rheological behaviors, the pectin solutions were a share-thinning non-Newtonian fluid. Microwave treatment had the greatest impact on fluid behavior at low concentrations of pectin. The microwave-induced degradation of pectin was fitted based on η] to a first-order kinetic model, and pectin at 0.5 g/100 mL was degraded fastest and at 1.5 g/100 mL slowest. Compared with the samples subjected to boiling without microwave treatment, microwave treatment also had non-thermal effects in pectin degradation.