Dynamics of fluid migration into porous solid matrix during high pressure treatment

A mathematical approach was used to describe the mechanism of pressure-driven flow during the holding period of high pressure processing (HPP). A lumped method was used for the estimation of mass transfer parameters using an analogy to Fick's second law. In addition, a least squares optimization algorithm was introduced as inverse parameter estimators to obtain the associated mass diffusivity coefficients. The approach was verified using a model system involving liquid diffusion (1% w/w ascorbic acid solution) into a porous solid matrix (apple cubes) under HPP conditions (100-600 MPa) with different holding times (0-30 min). The associated fluid diffusivity values ranged 4.38 × 10−9-2.19 × 10−8 m2 s−1. Finally, a simple linear model was fitted to the experimental data at 100 and 600 MPa which could be used to estimate the total porosity of the solid matrix. Thus, finite element numerical solutions combined with simple Fickian approach could be used to model the unsaturated liquid flow in to a porous solid matrix. The study also showed that the liquid in-flow decreased in blanched apples subjected to similar HPP confirming the need for a porous structure for the efficient liquid flow.