Thermal transitions of osmotically dehydrated tomato by modulated temperature differential scanning calorimetry

Abstract

Modulated temperature differential scanning calorimetry (MTDSC) was employed to examine thermal transitions of osmotically dehydrated tomato (Lycopersicon esculentum, var. Deborah). Tomato halves, soaked in sucrose solution (60% sucrose), sodium chloride (10% NaCl) and mixtures of salt-sucrose solution (60% sucrose-10% NaCl/40% sucrose-15% NaCl) for 3 h at 40 degreesC, were comminuted, freeze-dried for 48 It and kept in desiccator over saturated salt solutions at 25 degreesC until equilibrium was reached. A MTDSC 2920 (TA Instruments) was used in all tests. A cyclic modulation of +/- 0.5 degreesC/40 s was superimposed on a constant scanning ramp of 2.5 degreesC/min. Thermo-analytical curves of both osmotically dehydrated and untreated tomato allowed the determination of the glass transition data and the plot of state diagrams. Furthermore, a peak of enthalpy relaxation in the glass transition region that partially disappears on rescanning was detected. Structural recovery was modelled by Williams-Watts equation and glass transition temperature by Gordon and Taylor and Kwei equations. (C) 2002 Elsevier Science B.V. All tights reserved.