High hydrostatic pressure treatment effects on selected tissue properties of fresh horticultural products

High hydrostatic pressure (HHP) treatments affect the integrity and function of biomembranes and proteins of fresh produces. Initially, pressure affects membrane permeability, directly linked to a reversible decline in cell turgor. Reversibility reflects the restoration of intracellular solute gradients by re-established membrane semipermeability and functionality of membrane-bound proteins. Above a certain threshold, pressure effects become irreversible resulting in tissue damage. Combining cell pressure probe and tissue impedance measurements allows differentiation between reversible and irreversible effects. Thus, these parameters were comparatively investigated in both fresh red cabbage leaves and in radish tubers, species-specifically exposed to various predetermined relevant HHP conditions (red cabbage: 150-200 MPa at 35-55 degrees C for 5-20 min; radish: 100-200 MPa, at 20-40 degrees C for 5-10 min). These specific treatments facilitated the evaluation of the transition between reversible changes in membrane and protein properties and irreversible damages. While turgor declined immediately after HHP treatments, tissue damage occurred only delayed. The two products differed in their responses to various HHP conditions. Generally, HHP effects were limited and reversible at (and certainly also below) 100 MPa but were amplified with intensity of pressure treatments. Industrial relevance: Increasing food security aspects but also growing concerns against conventional thermal treatments demand the application of novel and gentle nonthermal hygienisation techniques such as high hydrostatic pressure (HHP) also for the production of fresh ready-to-eat salads. However, knowledge about potential impacts of different HHP ranges on metabolic functionality and freshness of fruits and vegetables, and thus produce quality, is still only sketchy. This study comprehensively differentiated the reversible and irreversible effects of processing conditions on the physiological and structural basis of HHP effects on fresh red cabbage leaves and radish tubers. It thus provides valuable information on the absolute limits of the applicability of HHP for safety of fresh produces. The fact that pressure treatments above 150 MPa always resulted in irreversible tissue damage indicated that even short-term HHP treatments at room temperature are not suitable for the gentle sanitation of perishable fresh produces but may probably be useful as quarantine measure against parasites and viruses.