Enthalpy Changes of Foods in Freezing and Thawing Processes (I)

A fabricated conduction calorimeter and its performance

Abstract

To know enthalpy changes of foods in low temperatures, a conduction calorimeter was fabricated by the authors.
The results obtained with sucrose solutions and other products were as follows.
1) From the measurements of freezing point (θ_fp) and melting point (θ_mp), both θ_fp and θ_mp were depressed as water contents decreased, but θ_fp did not agree with θ_mp. θ_fp shifted to lower temperatures as freezing rate increased. θ_mp was a little nearer to the calculated values than θ_fp.
2) From the measurements of specific heat, the experimental error of our calorimetry was within ±5%.
3) From the measurements of enthalpy changes, the effect of water contents on enthalpy (H) was predominant. H (293) and H (mp) decreased as water contents decreased. Ice crystal melted at lower temperatures as water contents decreased. Enthalpy increased in direct proportion to temperature increase in liquid zone, and the gradient decreased as water contents decreased.