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Activity of NaCl and carrageenan on thermal conductivity and enthalpy of frozen surimi prepared from Adriatic pilchard

Determination of apparent enthalpy H, initial freezing temperature Ti, and thermal conductiv-ity k of surimi in the temperature range from -25 oC to +5 oC by differential thermal analysis DTA and a system for measurement of thermal conductivity of food by the method of unsteady responses from a line heat source are presented. Samples of surimi were prepared in laboratory conditions from Adriatic pilchard with addition of carrageenan and NaCl. Water content in surimi was 81.5% before mixing with the added substances. For interpretation of experimental results and determination of thermophysical properties mathematical models of H(T) and k(T) are used, while Ti are determined from DTA curves. Values of k, H and Ti of surimi samples are correlated with mass fractions of NaCl (w = 0, 2, 4, 6, 8 and 10%) and carrageenan ( w = 2% ). Increase of mass fraction of NaCl from 0 to 10% results in decrease of Ti from -0.19 to -9.1 oC. Below Ti thermal conductivity k(T) of samples of surimi decreases with increase of mass fraction of NaCl which increase the ratio of unfrozen and frozen water. This effect is most clearly observed by the function of enthalpy H(T).

thermophysical properties; surimi; DTA; carrageenan

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