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 restrictedmolecular 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 (aw). The spin--spin relaxation timeT2 was 1 determined by means of low resolution 1H-NMR spectroscow 2 py and described in relation to the storage conditions and the glass transition temperature Tg. Compared to the disaccharides, dextran generally showed lower absolute T2 values and a weaker dependence on storage aw and temperature. For lactose and trehalose, the plasticising effect of water and temperature was significantly stronger. Their relaxation time T2 was shown to be only dependent on ∆T, the temperature distance to Tg. Furthermore, both disaccharides showed an increase in T2 already 20--40 °C below Tg.Thus, Tg in reference to T2 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 °C below Tg. Further comparison between T2 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 restrictedmolecular 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 (aw). The spin--spin relaxation timeT2 was 1 determined by means of low resolution 1H-NMR spectroscow 2 py and de...     »