Experimental Study of the Parameters of High Pulsed Electrical Field Pretreatment to Fruits and Vegetables in Vacuum Freeze-Drying

High pulsed electrical field as pre-processing step for fruits and vegetables in the vacuum freeze drying could increase drying rate efficiency and preserve nutritional ingredients in maximum. Moreover, high pulsed electrical field pretreatment has been successfully used to solve practical problems in the vacuum freeze drying, such as energy consumption, high production costs and long drying time etc. The drying experiments were conducted with apples which were pretreated by high pulsed electrical field, and the results showed that high pulsed electrical field pretreatment could increase the drying rate obviously. According to the range analysis, the optimal parameters of high pulsed electrical field for drying were obtained as follows: pulse strength was 1000 V•cm-1, pulse time was 120 μs, and pulse number was 30. By using the above optimal conditions, energy consumption per unit of water was reduced by 17.74%, freeze drying time was shortened by 22.50%, and productivity per unit area was increased by 28.50% than results of the untreated group. In addition, it was found that the most important physical factors of high pulsed electrical field which affected the vacuum freeze drying were the pulse duration, pulse strength and pulse number.