In this study, apple, guava and potato were dried in a heat pump dryer under inert environmental (nitrogen or carbon dioxide) conditions and the impact on colour, surface porosity and rehydration abilities were investigated. Lemon juice and peel were used as natural inhibitors to prevent browning in air drying of apples. Comparisons were made between heat pump dried samples and those dried by freeze and vacuum drying. Results showed that MAHPD low temperature drying at about 45 degrees C and relative humidity around 10% led to better physical properties, such as reduced shrinkage, decreased firmness and more porous structure of the materials, which resulted in quicker rehydration. When using inert gas, the colour of heat pump dried food was similar to vacuum or freeze drying. (c) 2005 Elsevier Ltd. All rights reserved.