Damage of cellular material under simultaneous application of pressure and pulsed electric field

Influence of pulsed electric field (PEF) simultaneous to pressure treatment on moisture expression from fine-cut cellular raw material has been investigated. Dependencies of specific conductivity σ, liquid yield Y , instantaneous flow rate v and qualitative juice characteristics at different modes of PEF treatment are discussed. Three main consolidation phases were observed in a case of mechanical expression. A unified approach is proposed for liquid yield data analysis allowing to reduce the data scattering caused by differences in the quality of samples. Simultaneous application of pressure and PEF treatment allowed to reveal a passive form of electrical damage. Pressure provokes the damage of defected cells, enhances diffusion migration of moisture in porous cellular material and depresses the cell resealing processes. PEF application at a moment when a sample specific electrical conductivity reaches minimum and pressure achieves its constant value seemed to be the most optimal. Notation d mean cell's dimension, µm D diffusion coefficient, m 2 s −1 E electric field strength, kV cm −1 k area normalizing coefficient M 1 first Moment, s N number of pulses P pressure, bar S area under the expression curve Y (t), % s t i pulse duration, µs t max maximal time of pressing, s t p time of PEF treatment application, s t vmax time, where maximum of instantaneous flow rate is observed, s ∆t pulse repetition time, ms T temperature, K v = dY /dt instantaneous flow rate, % s −1 U external voltage, V W moisture content, % Y I first normalized form of liquid yield Y II second normalized form of liquid yield Y * intensification degree of PEF treatment Greek letters σ conductivity, S m −1 τ characteristic time of expression, s τ * coefficient of PEF enhanced durability τ D ∼ d 2 /6D time constant of diffusion process, s