The aim of this work was to evaluate whether, in case of freeze-dried bacteria, the protective effect of a surrounding glassy matrix can be ascribed to its inherent restricted molecular mobility. Lactobacillus paracasei ssp. paracasei together with three different protectants (lactose, trehalose and dextran) was freeze-dried and stored at different temperatures and water activities (a (w)). The spin-spin relaxation time T (2) was determined by means of low resolution H-1-NMR spectroscopy and described in relation to the storage conditions and the glass transition temperature T (g). Compared to the disaccharides, dextran generally showed lower absolute T (2) values and a weaker dependence on storage a (w) and temperature. For lactose and trehalose, the plasticising effect of water and temperature was significantly stronger. Their relaxation time T (2) was shown to be only dependent on a dagger T, the temperature distance to T (g). Furthermore, both disaccharides showed an increase in T (2) already 20-40 A degrees C below T (g). Thus, T (g) in reference to T (2) does not act as an absolute threshold. This fact could explain the finding of several publications that an absolute stability for freeze-dried bacteria can only be achieved 30-50 A degrees C below T (g). Further comparison between T (2) and the corresponding inactivation rates revealed that the relevance of mobility for the stability of lyophilisates is strongly temperature and system dependent. At low storage temperatures, a potential rate-limiting effect due to the lack of detrimental chemical and physical reactions is invisible. However, with increasing storage temperature, the restricted mobility is shown to become a rate limiting bottleneck. Thus, the harsher the environmental condition, the more relevant is the protective effect of a surrounding glassy matrix.     «

The aim of this work was to evaluate whether, in case of freeze-dried bacteria, the protective effect of a surrounding glassy matrix can be ascribed to its inherent restricted molecular mobility. Lactobacillus paracasei ssp. paracasei together with three different protectants (lactose, trehalose and dextran) was freeze-dried and stored at different temperatures and water activities (a (w)). The spin-spin relaxation time T (2) was determined by means of low resolution H-1-NMR spectroscopy and des...     »