Calorimetry and Pressure-shift Freezing of Different Food Products

Abstract

Rapid depressurisation can create uniform, small and abundant ice nucleation during pressure-shift freezing (PSF) which can then protect the frozen food structure from cell damage. The amount of depressurisation-formed ice was evaluated using a high-pressure calorimeter for different food products (tylose, potato, salmon, pork and water). Experiments were conducted at an initial pressure of 62, 82, 112, 156, 180 and 196MPa, at temperatures set at −5, −7, −10, −15, −18 and −20°C, respectively (slightly above the phase diagram of water-ice I). Calorimetric thermograms recorded during PSF tests were used for computing the quantity of ice formed based on heat balance. A polynomial relationship was established for each product to compute the depressurisation-formed ice ratio as a function of the initial pressure applied. This model accurately predicted the maximum ice ratio for PSF at a given pressure (0.1 to 210MPa) or the minimum ice ratio for PSF at a given temperature (−22 to 0°C). Moisture content was the major factor affecting the sample-mass based (SMB) ice ratio with higher moisture yielding a higher SMB ice ratio. A general relationship between water-mass based (WMB) ice ratio ( R'ice-water) and initial pressure was found from the pooled data from all tested products: R'ice-water 0.114 P+0.00022 P2 (R2 0.94, n 47) which agreed well with relevant literature values for pure water.