30 May 2005


A low-energy-consuming drying process that produces high quality products is desirable in food
industry. As heat pump dryer has a high Coefficient of Performance and could provide a satisfactory
drying condition for heat-sensitive foods at a relatively low cost. Since the drying system operates in
a closed loop, the air can be replaced by an inert gas to yield a modified atmosphere, thus eliminating
oxygen, which causes most of the deteriorative quality changes in dried products due to oxidation. In
this study, some temperature sensitive materials such as guava and papaya were dried in heat pump
dryer using normal air, carbon dioxide and nitrogen. These materials were also dried in vacuum dryer
and freeze dryer under similar conditions. The drying kinetics and quality of these dried fruits
resulting from different drying methods were investigated and compared. The change of color,
porosity, and loss of vitamin C were evaluated to identify the potential of modified atmosphere heat
pump drying. Experiments showed that introducing inert gas as drying medium made much
improvement of foods’ quality, which led to a better physical appearance, quicker rehydration and
better retention of nutrients.