A new method for the measurement of added glaze on frozen foods

Abstract In this work the ice glaze on frozen foods such as cooked, peeled prawns has been measured by dissolving the ice in a solvent at known temperatures and measuring the change in the dielectric properties of the solvent. This change was calibrated for known water contents and hence the glaze could be deduced. It has been found that the glaze measured at sub-zero temperatures, where it was hoped that no tissue water would dissolve, is somewhat larger than that expected either from the CODEX standard reference method or from direct measurement of the weight gain during processing. It is however consistent and reproducible for a given product. Measurements of the glaze by three independent operators using the Codex method gave extremely variable results. It is suggested that the measured value is a combination of water added during glazing, that held on the surface after cooking, peeling and washing in dilute brine and that water which remains unfrozen due to eutectic like behaviour. In addition, perhaps that which is released from the tissue during freezing by damage to cell walls, under the influence of temperature gradients and fluctuations during storage could migrate to the surface. However, even though the storage conditions were not ideal, no effect of time after freezing was seen in the results. Using the same procedure at temperatures above zero coupled with a conductivity measurement of the solution allowed the determination of the time at which the superficial glaze was all removed and the transition to extraction of other water took place.