Water, ice and sucrose behavior in frozen sucrose–protein solutions as studied by 1H NMR

This work aimed at characterizing both the spin–spin (T2) and spin–lattice (T1) relaxations of water in frozen samples. Pure water and aqueous solutions (sucrose and/or casein) were studied, temperatures ranging from −13 to 20 °C. Three relaxation components could be distinguished after signal fitting. For example, the shorter spin–spin relaxation time was only observed at the frozen state and attributed to the ice crystals protons and the longer relaxation time was attributed to the liquid water and some of the sucrose protons. The exploitation of the ‘solid’ relaxation parameters gave information on ice content (T2) and on ice structure (T1). The method developed for ice content calculation was coherent with calorimetric data. The changes in the spin–spin relaxation of sucrose protons with temperature showed that at low temperature (−13 °C) it could be fully distinguished from the relaxation of water protons and at positive temperature this discrimination was not possible anymore.