CONICET | Buscador de Institutos y Recursos Humanos

Galacto-oligosaccharides (GOS) are important prebiotic substances with interesting technological and nutritional properties. The ability of GOS to protect Lactobacillus delbrueckii subsp. bulgaricus upon freeze-drying was analyzed on the basis of their capacity to form glassy structures. Glass transition temperatures (Tg) of a GOS matrix at relative humidities (RH) within the range 11-80 % were determined by DSC. Survival of L. bulgaricus in a glassy state GOS matrix was investigated after freezing, freeze-drying, equilibration at RH equal to 11, 22 and 33 % (those where the matrix remains in a glassy state at room temperature) and storage at different temperatures (4, 20 and 32 ºC). At 32 ºC, a drastic loss of viability was observed in all conditions assayed. At 20 ºC, the survival was affected by the water content, being the samples stored at lower RH, those depicting the highest survival percentages. At 4ºC, no decay in the cells count was observed after 45 days of storage. The incorporation of propidium iodide (PI) into the freeze-dried microorganisms indicated that the presence of GOS matrix is not sufficient to prevent membrane damage. The correlation between molecular mobility [as measured by Proton nuclear magnetic resonance (1H NMR)] and loss of viability explained the efficiency of GOS to preserve L. bulgaricus. The preservation of microorganisms was improved at low molecular mobilities and this condition was obtained at low water contents and low storage temperatures. This integrated study about the thermophysical properties of GOS and their relation with the cell-sugar matrix provides information that could be important for the development of new functional foods containing pre and probiotics.