Effect of Process Parameters on Quality Properties of Microwave Dried Red Pitaya (Hylocereus costaricensis)

Abstract

The effect of microwave power density on the microwave drying of red pitaya (Hylocereus costaricensis) was investigated using a small modified commercial microwave. Microwave power density was varied in the range of 5.47 to 19.02 W/g. The ambient, internal sample and sample surface temperatures, and moisture loss were measured during microwave drying at various microwave power densities. The drying rate increased with increasing power density. The temperature profiles rapidly reached their saturation level. The experimental moisture loss data were fitted to the Tang and Cenkowski drying model using a value of residual sum of squares (RSS) to evaluate the goodness of fitting the model. The dried product was analysed to examine the quality such as color, shrinkage, tensile hardness and structure. The results showed that the color change is higher at higher power density and temperature because of the faster browning rate and faster drying rate. The beginning of the color change corresponded closely to the beginning of the falling rate period. The microwave drying also caused the red pitaya to shrink to a greater extent of up to 70% at higher power density because of the faster drying rate. The internal structure also tended to collapse during microwave drying.