High hydrostatic pressure effects on membrane-related quality parameters of fresh radish tubers

The impacts of high hydrostatic pressure (HHP) treatments on metabolic functionality and quality of fruit and vegetables are still poorly understood. The effects of pressure intensity (100, 150 and 200 MPa) and holding time (5 and 10 min), and temperatures (20, 30 and 40 degrees C) during HHP treatment on fresh radish tubers has been studied. Colour, stiffness and turgor of the tubers were evaluated using colorimetry, texture analyses and direct turgor measurements with the cell pressure probe techniques. Comparison of turgor and stiffness losses, and colour changes, of skin and thin-walled parenchymatous inner radish tissue showed the effects of the various HHP treatment parameters on the permeability of biomembranes. HHP treatment resulted in a rapid reduction of cell turgor and, concomitantly of tuber stiffness, but also in a cellular redistribution of anthocyanins as indicated by colour changes. These responses were partially reversible up to 100 MPa applied pressure at 20-40 degrees C for 5-10 min, yielding a turgor threshold of 0.1 MPa. Beyond these limits, changes were irreversible, most probably due to the denaturation of membrane bound proteins such as ion channels and pumps. Overall, even short-term HHP treatments at room temperature are not suitable for sanitation by inactivating bacteria of perishable produce.