Microwave Vacuum–Assisted Drying of Green Peas Using Heat Pump and Fluidized Bed: A Comparative Study Between Atmospheric Freeze Drying and Hot Air Convective Drying

Abstract

This study investigates the performance of microwave vacuum–assisted drying (MVD) of green peas using both fluidized bed and heat pump systems. A comparative study of heat pump–fluidized bed atmospheric freeze drying (HP-FB-AFD) and heat pump–fluidized bed hot air convective drying (HP-FB-HACD) was conducted. The initial drying rates of green peas were 0.04 and 0.12 1/min for HP-FB-AFD and HP-FB-HACD, respectively. Moisture diffusivity of green peas dried in HP-FB-HACD and HP-FB-AFD were 1.04 × 10⁻⁹ and 6.94 × 10⁻¹¹ m²/s, respectively. HP-FB-AFD did not entail changes in the starch granules and preserved the sample size and shape with minimal shrinkage (20%), whereas HP-FB-HACD generated significant volumetric shrinkage (50%). HP-FB-AFD+MVD created a desirable porous inner structure of the final product. HP-FB-HACD+MVD significantly increased the hardness of the dried product and produced green peas with a compact structure and tightly packed cells. Neither HP-FB-AFD+MVD nor HP-FB-HACD+MVD significantly influenced the color of dried green peas. To respond to the current demand for high-quality products, the multistage combined HP-FB-AFD+MVD method is an interesting technique for green peas processing.

Keywords:

• Atmospheric freeze drying
• Fluidized bed
• Green peas
• Heat pump
• Hot air convective drying
• Microwave vacuum drying

ACKNOWLEDGMENTS

This study was financially supported by the Scholarship and Training Fund established within the EEA Financial Mechanism and Norwegian Financial Mechanism through projects FSS/2011/V/D3/W/0103 and FSS/2011/V/D3/W/0102.

Notes

Code: 1 = control; 2 = MVD; 3 = HACD; 4 = HP-FB-AFD; 5 = HP-FB-AFD+MVD; 6 = HP-FB-HACD; 7 = HP-FB-HACD+MVD.

Code: 1 = control; 2 = MVD; 3 = HACD; 4 = HP-FB-AFD; 5 = HP-FB-AFD+MVD; 6 = HP-FB-HACD; 7 = HP-FB-HACD+MVD.

Mean values within the same column followed by the same letter are not significantly different at p ≤ 0.05.

Code: 1 = control; 2 = MVD; 3 = HACD; 5 = HP-FB-AFD+MVD; 7 = HP-FB-HACD+MVD.

Mean values within the same column followed by the same letter are not significantly different at p ≤ 0.05.

Code: 1 = control; 2 = MVD; 3 = HACD; 4 = HP-FB-AFD; 5 = HP-FB-AFD+MVD; 6 = HP-FB-HACD; 7 = HP-FB-HACD+MVD.

Mean values within the same column followed by the same letter are not significantly different at p ≤ 0.05.