The shrinkage of orange slices during microwave drying and ohmic pretreatment

The present research was an attempt to investigate the effect of ohmic pretreatment on the shrinkage of orange slices during the microwave drying and check the effect of this heating process on the shrinkage percentage of the samples. Thomson oranges were chopped into 4-mm-thick slices and were then arranged in a way that they can fit into the ohmic heating system. The ohmic heating system consisted of a 10-mm-thick rectangular glass cell (11 × 8 × 15 cm3) with two 8 × 15 cm stainless steel 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, the orange slices were subjected to microwave drying at three power levels (90, 360, and 900 W). During the microwave drying process, samples were photographed and weighed at 1-min intervals to check the shrinkage percentages. The experiment was carried out with three replicates. The results showed that the use of ohmic heating system as pretreatment leads to a decline in the moisture content of orange slices. In other words, an increase in duration of heating (from 3 to 7 min) intensifies the moisture content reduction rate. During the microwave heating process, any rise in microwave power (from 90 to 900 W) led to intensification of orange slice shrinkage level. Practical applications The present research was carried out in an attempt to increase productivity of dehydration in the industrial sector and also in the fruit dehydration industry. This research was also an attempt to investigate and predict the shrinkage rate of orange slices subjected to microwave dehydration and investigate the effect of ohmic pretreatment on the shrinkage percentage of the specimens in an attempt to figure out if this method can be used as an alternative to other industrial methods.