High pressure impregnation (HPI) of apple cubes: Effect of pressure variables and carrier medium.

High pressure impregnation (HPI) is a novel technique to infuse desired fluids into porous biomaterials. In this study, the effect of 24 different pressure-time combination treatments were studied: come-up time (0 to 6 min), pressurization rate [100, 150, 200, 300 (MPa/min)] and pressure holding times (0-30 min) at 100, 300 & 600 MPa. Experiments were carried out based on HPI of ascorbic acid (AA) as a low viscosity aqueous (1%) Newtonian fluid. AA infusion reached 215 to 250 mg/kg when reaching operating pressure of 200 MPa irrespective to pressurization rate or come-up time. A model for the entire process was developed based on the combination of a first-order kinetics during the come-up time and a linear diffusion process during pressure holding time. In addition, impregnation of 0.5%, 1%, 2%, and 4% chitosan (CH) into apple cubes, as a high viscosity non-Newtonian carrier fluid, showed a quadratic trend for CH uptake. Moreover, HPI pre-treatment with CH prior to freezing demonstrated significant reduction in texture breakdown and drip loss in frozen-thawed apple cubes. Finally, microstructural studies were also carried out, and the microscopic images showed a progression of perpendicular flow paths at the peripheral layers as well as certain cellular rearrangements.