The shrinkage of orange slices during microwave drying and ohmic pretreatment

摘要

The present research was an attempt to investigate the effect of ohmic pretreatmenton the shrinkage of orange slices during the microwave drying and check theeffect of this heating process on the shrinkage percentage of the samples. Thomsonoranges were chopped into 4-mm-thickslices and were then arranged in a way thatthey can fit into the ohmic heating system. The ohmic heating system consisted ofa 10-mm-thickrectangular glass cell (11 × 8 × 15 cm~3) with two 8 × 15 cm stainlesssteel electrodes and a voltage regulator. Samples were tested at three voltage gradients(30, 50, and 70 V) for 3, 5, and 7 min. After the heat treatment process, theorange slices were subjected to microwave drying at three power levels (90, 360,and 900 W). During the microwave drying process, samples were photographed andweighed at 1-minintervals to check the shrinkage percentages. The experiment wascarried out with three replicates. The results showed that the use of ohmic heatingsystem as pretreatment leads to a decline in the moisture content of orange slices. Inother words, an increase in duration of heating (from 3 to 7 min) intensifies the moisturecontent reduction rate. During the microwave heating process, any rise in microwavepower (from 90 to 900 W) led to intensification of orange slice shrinkage level.