Microwave and microwave-vacuum drying kinetics of field peas

Abstract

Field pea (Pisum sativum L.) is a leguminous crop high in protein and complex carbohydrates and low in fat. Field pea is harvested at 18 to 20% moisture and must be dried to lower moisture contents for safe storage and grinding to be used in food applications. The drying kinetics of field pea using microwave, microwave-vacuum and convective drying were investigated. Three microwave power levels P10, P8 and P6 corresponding to 745, 588 and 455 W, respectively and two vacuum pressures 85 and 68 kPa were used. The times required to dry field pea samples from initial moisture content of 21.1% to below 10% decreased with increasing power levels. Higher drying times were achieved when higher vacuum pressure of 85 kPa was combined with the microwave power levels compared to combined vacuum pressure of 68 kPa and microwave power levels, as well as microwave power levels alone. However, the decrease in drying time from using combined higher vacuum pressure and microwave power was marginal. There was no difference between the drying times for samples dried at microwave power levels P10, P8 and P6 and the corresponding drying at combined vacuum pressure of 68 kPa and power levels P10, P8 and P6. Page and modified Page's models provided best fit models for the microwave, microwave-vacuum and convective drying data with higher R2 and lower SE compared Newton and Wang and Singh models. The drying rate constant (k) values ranged from 0.0088 to 0.0245 min-1 for the Page's model and for the modified Page's model, they varied from 0.0484 to 0.0916 min-1. The n values ranged from 1.3079 to 1.8875 for both Page and modified Page's models.