High pressure–low temperature processing of foods: impact on cell membranes, texture, color and visual appearance of potato tissue

To design and optimize high pressure processes at low temperatures, a quantification of the effects of different processing steps on the food structure is required. Beside pressure-shift freezing, the processes of freezing to ice III and ice V, as well as storage at −27 °C and 250 MPa up to 24 h (metastable liquid state of water) of potato samples were examined. Analyses of the structural changes of the plant tissue included impedance measurements, texture analysis, color measurements and the evaluation of the optical appearance. Storage at subzero temperatures without phase transitions resulted in low membrane damage; however, cell lysis was triggered. Freezing to ice III resulted in the lowest damaging effect on the tissue compared to the other phase transition processes investigated. Samples frozen to ice V and pressure-shift frozen were more deteriorated compared to those frozen to ice III. However, considerable improvements compared to conventional freezing were found. The direction of solid–solid phase transitions (phase transition of ice I to ice III or phase transition of ice III to ice I) influenced the result of high pressure–low temperature processing significantly. It was previously shown that pressure supported phase transitions of ice I like pressure shift freezing are able to preserve the fragile stucture of biological samples like food better than conventional freezing. The present study extends the knowledge of pressure supported phase transitions to a higher pressure domain with the participation of other ice modifications. The authors demonstrate the influences of high pressure phase transitions of water on plant tissue material depending on the processing conditions. The study opens the way to new industrial processing concepts based on high pressure low temperature applications.