Effect of High Pulsed Electric Field Pretreatment on Dielectric Constant of Apples

Message obtained by dielectric properties measuring of biological materials could be used for process monitoring and quality assessment of agricultural products. High pulsed electric field pretreatment can improve the efficiency of subsequent processing and influence the quality of agricultural products. Analysis of dielectric constant change of high pulsed electric field pretreated materials would contribute to understanding mechanism of high pulsed electric field and optimizing processing technology of agricultural products. Our present study is devoted to investigation the effect of high pulsed electric field treatments on apple tissue. Dielectric constant were measured before and after apple samples were subjected to HPEF treatments using varying field strengths of 1 kV/cm, 2 kV/cm and 3 kV/cm, pulse number of 92, pulse duration of 65 mu s and pulse interval of 500 ms. Frequency characteristics of dielectric constants of apple tissues were analyzed over selected frequency ranges. Changes in dielectric constants versus time were detected before and after high pulsed electric field pretreatments within 30 min. Certain regularity were found in the apple dielectric constant change after different pretreatments: decreases in dielectric constants with increases in frequency were observed both in pretreated and untreated apple samples, but the degrees of reduction were different; at most test point during 30 min after high pulsed electric field pretreatment, values of dielectric constant were lower as compared to those at preceding time points except individual ones. The variation of dielectric constant after pretreatment of 3 kV/cm showed obvious differences from variations of another two.