Effect of relative humidity on microwave drying of carrot

• The humidity of the convection air was changed by using different flow rates and complementary water.
• The humidity affected the drying rate as well as the product quality significantly.
• High humidity showed benefit to the quality but extended the drying duration.
• Accelerated air flow would be a compromise proposal between the drying rate and quality.

The aim of this study is to investigate the influence of the relative humidity on the product quality during microwave drying process. A new microwave drying system with humidity control was developed. Twelve schemes were planned in the experiments, for the purpose of changing the relative humidity of the convection air. The relationship between the humidity and the drying rate as well as the product quality were discussed. Nonparametric ANOVA and multiple comparisons were conducted. Results showed that the complementary water method could provide the best product quality, followed by the accelerated and low rate air flow schemes. High flow rate and decelerated air schemes should be avoid if the product quality is of utmost consideration. The accelerated air schemes should be a compromise proposal if the drying rate is also concerned.