Solid–liquid expression from denaturated plant tissue: Filtration–consolidation behaviour

The objective of this study is to investigate the filtration–consolidation behaviour of biological tissue (sugar beet specimens), denaturated by pulsed electric field (PEF) and freezing–thawing pretreatments. The degree of cell membrane damage was evaluated by the tissue electrical conductivity measurement (determination of the cell disintegration index Z). The PEF-treated and freeze–thawed tissues show different structure response on the applied compressive pressure and different filtration–consolidation behaviour. The value of fracture pressure (Pf ≈ 58.5 bar) is the lowest and the value of tissue deformation under fracture (εf ≈ 0.46) is the highest for sugar beet tissue treated by freezing/thawing. PEF treatment leads to more rigid and more fragile tissue structure (Pf ≈ 63.8 bar, εf ≈ 0.28) than freeze–thawed tissue. Untreated tissue seems to be stronger and less fragile than the PEF-treated tissue (Pf ≈ 84.1 bar, εf ≈ 0.37). Different tissue reactions on the loading pressure evidently reflect the difference between microstructures of treated and untreated tissues. The filtration/consolidation behaviour during liquid expression from a sugar beet tissue also depends on the type and degree of structure denaturation. Tissues treated by PEF and freezing/thawing demonstrate two consolidation stages of expression (primary and secondary). However, the freeze–thawed tissue tends to modify the expression mechanism under the higher loading pressure (60 bar) with approach to the primary consolidation behaviour. The simplified semi-empirical consolidation model permits a reasonably good prediction of expression behaviour from the denaturated sugar beet tissue and estimation of consolidation coefficient b under different pressures. The extrapolation of curves b(P) shows the value of hypothetical pressure, Pmax ≈ 90 bar at which the consolidation behaviour would be similar to both PEF-treated and freeze–thawed tissues.