Drying of banana slices using combined low-pressure superheated steam and far-infrared radiation

A concept of combining the already proven low-pressure superheated steam drying with far-infrared radiation (LPSSD-FIR) was proposed and studied as a novel drying technology for heat-sensitive products in the present study. The effects of various operating parameters, i.e., drying medium temperature and pressure, on the drying kinetics and dried product quality (in terms of color, shrinkage, rehydration behavior, microstructure and texture) of banana, which was used as a model heat-sensitive material, were investigated. Comparison was also made with similar sets of data obtained from the system with combined far-infrared radiation and vacuum drying (VACUUM-FIR) conducted in the same drying chamber. The results showed that the temperature of both LPSSD-FIR and VACUUM-FIR samples during the later stage of drying were higher than the pre-determined medium temperatures. It was also found that LPSSD-FIR took longer drying time than VACUUM-FIR at almost all drying conditions except at the highest drying temperature tested (90 degrees C). Although the drying time of LPSSD-FIR at the highest drying temperature studied was the shortest and dried banana slices obtained had more crispness, this condition gave dried banana slices with excessive changes of lightness and redness (darker color). Therefore, LPSSD-FIR at 80 degrees C was suggested as the best drying condition in this study. (c) 2007 Elsevier Ltd. All rights reserved.