Effects of intermittent CO 2 convection under far-infrared radiation on vacuum drying of pre-osmodehydrated watermelon.

BACKGROUND: Watermelon, a tropical seasonal fruit with high nutrient content, requires preservation through drying due to its perishable nature. Nevertheless, drying of watermelon through conventional processes has a negative impact either on the drying time or on the final product quality. In this work, osmotic dehydration of watermelon followed by far-infrared radiation-assisted vacuum drying (FIRRAVD) was optimized to develop dehydrated watermelon with minimum moisture content. Significantly, during FIRRAVD, an attempt was made to further intensify the drying rate by forced convection through intermittent CO2 injection. Drying kinetics of each operation and physicochemical qualities of dried products were evaluated.

RESULTS: FIRRAVD was a viable method of watermelon drying with appreciably high moisture diffusivity (Deff,m ) of 4.97 × 10-10 to 1.49 × 10-9 m2 s-1 compared to conventional tray drying. Moreover, intermittent CO2 convection during FIRRAVD (ICFIRRAVD) resulted in appreciable intensification of drying rate, with enhanced Deff,m (9.93 × 10-10 to 1.99 × 10-9 m2 s-1 ). Significantly, ICFIRRAVD required less energy and approximately 16% less time compared to FIRRAVD. The quality of the final dehydrated watermelon was superior compared to conventional drying protocols.

CONCLUSIONS: The novel CO2 convective drying of watermelon in the presence of far-infrared radiation demonstrated an energy-efficient and time-saving operation rendering a dehydrated watermelon with acceptable quality parameters. © 2017 Society of Chemical Industry.