For the real time measurement of temperature of the sample during freezing an optical fiber was placed in the center of the sample and connected to an optical fiber station (OSB system Fiso, Québec, Canada) which in turn was connected with a PC
provided with proper data logging software (FISOCommander Workstation Edition v1.10.9 Fiso Technologies Inc. Québec, Canada). The data acquisition rate was at 1 Hz.