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

• Published in: Drying technology 2013-04, Vol.31 (6), p.633-642
• Main Authors: Zielinska, M, Zapotoczny, P, Alves-Filho, O, Eikevik, T. M, Blaszczak, W
• Format: Article
• Language: English
• Subjects: air; Atmospheric freeze drying; color; Comparative analysis; diffusivity; dry peas; Drying agents; Fluidized bed; Fluidized bed boilers; fluidized beds; freeze drying; Freezing; Green peas; hardness; heat; Heat pump; heat pumps; Hot air convective drying; Microwave heating; Microwave vacuum drying; Peas; shrinkage; starch granules
• ISSN: 1532-2300; 0737-3937; 1532-2300
• DOI: 10.1080/07373937.2012.751921

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.