Drying characteristics of apple slabs after pretreatment with supercritical CO₂

Supercritical CO₂ pretreatment before dehydration leads to a faster dehydration rate. The best supercritical CO₂ pretreatment conditions for the most effective dehydration were 45°C, 25 MPa and 55°C, 25 MPa. Increasing pressure of the supercritical CO₂ pretreatment system tended to accelerate the dehydration rate more than increasing temperature did. Samples pretreated at higher temperatures and pressures showed greater shrinking and pore distribution on scanning electron microscopy. Control samples maintained their cell walls, whereas samples pretreated at higher temperatures and pressures showed more cell disruption, and more pores were observed. Pore sizes of control and pretreated samples were about 100 and 70∼80 μm, respectively. Samples pretreated at higher temperatures and pressures had smaller pores and a denser distribution.