Pulsed electric field treatment of apple tissue during compression for juice extraction

The influence of pulsed electric field (PEF) simultaneous to pressure treatment on juice expression from fine-cut apple raw material has been investigated. Dependencies of specific conductivity sigma, juice yield Y, instantaneous flow rate nu and qualitative juice characteristics at different modes of PEF treatment are discussed. Three main compression phases were observed in a case of mechanical expression. A unified approach is proposed for juice yield data analysis allowing a reduction in data scattering caused by differences in the quality of samples. Simultaneous application of pressure and PEF treatment revealed a passive form of PEF-induced cell plasmolysis. Pressure provokes the damage of defect cells, enhances diffusion migration of moisture and depresses the cell resealing processes. PEF application at the moment when the press-cake's specific electrical conductivity reaches a minimum and the pressure achieves its constant value seemed to be the most optimal. It has been found that a combination of pressing and PEF treatment gives the optimum results and enhances the yield of juice significantly and improves its quality. (C) 2001 Elsevier Science Ltd. All rights reserved.