Evaluation of glass transition of frozen foods. A benchmark of selected methods using conventional DSC and modulated DSC. Application to selected food samples

LE BAIL, A; TIRONI, V. A.; DE LAMBALLERIE, M

Copenague (Dinamarca)

Congreso; European Congress of Chemical Engeenering – 6 (ECCE-6); 2007

Differential scanning calorimetric is a useful tool to determine phase transition in food systems. The glass transition is often indicated as an important parameter to determine the optimal temperature for frozen storage. Storage at temperature lower than the glass transition temperature is supposed to reduce quality changes during prolonged storage. Several protocols can be used to evaluate the glass transition temperature of frozen foods, and might result in quite different values. This paper gathers results obtained recently in an in depth comparison test applied to sea food and to a cell suspension. Several methods using conventional scanning and modulated scanning (MDSC) were compared with different experimental conditions (heating rate, annealing step application). It shows that the protocol used can have an impact on the result. Conventional scanning was for most of the case more efficient in determining Tg even though modulated DSC appeared to be also efficient in some cases. Bacillus subtilis 168 was used as a model cell suspension. Cells were studied either as pellets obtained by centrifugation or as cell suspension in 50 mM ACES (N-[2-acetamido]-2-aminoethene-sulfonic acid) buffer (pH = 7.0, adjusted with NaOH) at a concentration of 104 cells/ml (suspension 104 cells/ml). Results show that Tg of cells may be identified in the case of pellets, being between -20 and -25 °C according to the system analyzed. Sea bass (Dicentrarchus labrax) muscle was also used as a model system. Tg around –15°C was identified in this case.