Enthalpy Determination of Frozen Surimi by Differential Thermal Analysis

D. Kovačević, Ž. Kurtanjek

Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, 41000 Zagreb

Article history:
Received July 20, 1993
Accepted December 30, 1993

Summary:
This work presents the results of determination of the enthalpy of frozen surimi by using the differential thermal analysis (DTA) method. Samples of surimi were prepared in laboratory conditions from Sardina pilchardus with addition of mixture of sorbitol and sucrose (S/S) in mass ratio of 1:1 and mass fraction of sodium tripolyphosphatc was 0.3 %. A DTA apparatus for on-line measurement and computer monitoring with high temperature sensitivity of 10 mK and high frequency sampling rate, 3500 readings in a second, was designed. Based on quantitative analysis of DTA results a model for determination of enthalpy in temperature range from -25 °C to temperatures of initial freezing points zvas developed. The model is based on the application of collocation technique for numerical approximation of the partial differential equation for heat transfer. Enthalpies of the samples with mass fractions of (S/S) from 0 to 12 % were determined. The DTA analysis yielded a linear relationship between initial temperatures of freezing and mass ratio of (S/S). For the regression model value of correlation coefficient r = 0.98 was established. Enthalpies determined by DTA arc in very good agreement with data from regression models based on calorimetric measurements. Experimentally obtained functional relationship between enthalpy, temperature and mass fraction of the cryoprotective mixture shows an increase in enthalpy as a function of the level of the mixture of sorbitol and sucrose (S/S), even at temperature of -20 °C, which is due to unfrozen water resulting from the cryoprotectant function of the (S/S) mixture.