The influence of static pressure on dielectric property and intracellular moisture of apple

The dielectric parameters of compressed apple in various pressures were monitored by parallel plate electrode and the electrical impedance spectroscopy ( EIS) was monitored by stainless steel needle electrode and the resistance of intracellular fluid and extracellular fluid and the change of volume distribution of intracellular fluid and extracellular fluid were calculated by Hayden equivalent circuit model. The results were as follows: relative dielectric constant and loss factor were nonlinear increase with static pressure increase when the pressure was less than 120 N, and were linear increase under the pressure of more than 120 N.Under the same static pressure, relative dielectric constant decreased with the loading frequency increase and loss factor existed in minimum value at 20 k Hz. With the static pressure increasing, the intracellular resistance increased, and extracellular resistance remained unchanged less than 120 N then increased. During static pressure increase to 250 N, the volume percentage of extracellular fluid increased from 5.69% to 9.22%. The relative dielectric constant, loss factor and the volume percentage of extracellular fluid was significant positive correlation and correlation coefficient was more than 0.94, in which account for the volume percentage of extracellular fluid was the main reason of dielectric parameters change.The work is hopeful to find a new idea for simultaneous monitoring physiological state of compressed fruit, and also provides theoretical guidance for rapid revaluation damage degree of fruit and realizing fruit grading by dielectric property.