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- Document type:
- Zeitschriftenaufsatz
- Author(s):
- Higl, B.; Kurtmann, L.; Carlsen, C. U.; Ratjen, J.; Först, P.; Skibsted, L H.; Kulozik, U.; Risbo, J.
- Title:
- Impact of water activity, temperature, and physical state on the storage stability of Lactobacillus paracasei ssp. paracasei freeze-dried in a lactose matrix
- Abstract:
- The aim of this study was to determine whether the combined effect of water activity and temperature on inactivation rates of freeze-dried microorganisms in a lactose matrix could be explained in terms of the glass transition theory. The stabilized glass transition temperature, Tg, of the freeze-dried products was determined by differential scanning calorimetry at two different temperatures, T (20 and 37 degrees C), and different water activities (0.07-0.48). This information served as a basis for defining conditions of T and water activity, which led to storage of the bacteria in the glassy (T < Tg) and nonglassy (T > Tg) states. The rates of inactivation of the dry microorganisms subjected to different storage conditions were determined by plate counts and could be described by first-order kinetics. Rates were analyzed as a function of water activity, storage temperature, and the difference between Tg and T. Inactivation below Tg was low; however, Tg could not be regarded as an absolute threshold of bacteria stability during storage. When the cells were stored in the nonglassy state (T > Tg), inactivation proceeded faster, however, not as rapid as suggested by the temperature dependence of the viscosity above the glass transition temperature. Furthermore, the first-order rate constant, k, was dependent on the storage temperature per se rather than on the temperature difference between the glass transition temperature and the storage temperature (T - Tg).
- Keywords:
- Bacteria/metabolism; Biotechnology/instrumentation/methods; Cold Temperature; Freeze drying; Glass; Kinetics; Lactobacillus/metabolism; Lactose/chemistry; Specimen Handling; Temperature; Water/chemistry; X-Ray Diffraction
- Journal title:
- Biotechnology Progress
- Year:
- 2007
- Journal volume:
- 23
- Journal issue:
- 4
- Pages contribution:
- 794--800
- Fulltext / DOI:
- doi:10.1021/bp070089d
- Print-ISSN:
- 8756-7938
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