The Contribution of the Inherent Restricted Mobility of Glassy Sugar Matrices to the Overall Stability of Freeze-Dried Bacteria Determined by Low-Resolution Solid-State 1H-NMR

Mathias Aschenbrenner, Eva Grammueller, Ulrich Kulozik, Petra Foerst

Publikation: Beitrag in FachzeitschriftArtikelBegutachtung

9 Zitate (Scopus)

Abstract

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 1H-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 {increment}T, the temperature distance to T g. Furthermore, both disaccharides showed an increase in T 2 already 20-40 °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 °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.

OriginalspracheEnglisch
Seiten (von - bis)1012-1024
Seitenumfang13
FachzeitschriftFood and Bioprocess Technology
Jahrgang7
Ausgabenummer4
DOIs
PublikationsstatusVeröffentlicht - Apr. 2014

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