UC Berkeley

Isochoric freezing is a pressure freezing technique that could be used to retain the beneficial effects of food storage at temperatures below their freezing point without ice damage. In this study, potato cylinders were frozen in an isochoric system and examined using full factorial combinations of three processing procedures (immersed in water, vacuum-packed and immersed in ascorbic acid solution), four freezing temperatures/pressures (-3 °C/37 MPa, -6 °C/71 MPa, -9 °C/101 MPa and -15 °C/156 MPa) and two average compression rates (less than 0.02 and more than 0.16 MPa/s). The effects of process variables on critical quality attributes of frozen potatoes after thawing were investigated, including mass change, volume change, water holding capacity, color and texture. Processing procedure and freezing temperature/pressure were found to be highly significant factors, whereas the significance of the compression rate was lower. For the processing procedures, immersion in an isotonic solution of 5% ascorbic acid best preserved quality attributes. At the highest pressure level of 156 MPa and low compression rate of 0.02 MPa/s, potato samples immersed in ascorbic acid retained their color, 98.5% mass and 84% elasticity modulus value. These samples also showed a 1% increase in volume and 13% increase in maximum stress due to pressure-induced hardening.