Characterization of high hydrostatic pressure effects on fresh produce cell turgor using pressure probe analyses

To improve the safety of fresh high quality convenience products, high hydrostatic pressure treatments (HHP) may provide a gentle, quality retainion alternative to traditional chemical preservation. However, information about the potential impact of HHP on metabolic functionality of fresh produce is rare; the few published studies indicate HHP has effects on physiological activity. These effects were highly product specific due to pronounced variations in both pressure sensitivity and stress responsivity. Biomembranes generally seem to be major physiological targets of HHP treatments. Cell turgor inevitably requires fully intact cell membranes. Turgor has an important impact on the fresh appearance of fresh produce, especially texture. Up to now, there is no investigation available that has directly evaluated the effects of HHP treatments on turgor of fresh vegetable tissue. In this study, the pressure probe technique was applied to comprehensively analyse the turgor of red cabbage tissue by directly measuring the hydrostatic pressure of individual cells. The effects of HHP on the cell turgor were tested at pressures ranging between 150 MPa and 250 MPa, applied for 5, 10, 15 and 20 min. As pronounced changes in pressure could result in related temperature changes, the effects of temperature (35 °C to 55 °C) on turgor was characterised separately. At 35 °C and 45 °C, leaf turgor transiently declined after HHP treatment of 150 MPa (for up to 10 min) but recovered again within 24 h; at 55 °C, however, it irreversibly dropped to near zero. The same occurred when HHP of 175 MPa or above was applied. In general, HHP treatment and temperature increases as well as the duration of treatments interactively affected cell turgor of red cabbage leaves. Critical process parameters derived for gentle application of HHP were 150 MPa at 45 °C for 10 min treatment time.