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Freeze-drying of Lactobacillus coryniformis Si3-effects of sucrose concentration, cell density, and freezing rate on cell survival and thermophysical properties.

Author(s) : SCHOUG A., OLSSON J., CARLFORS J., et al.

Type of article: Article

Summary

Freeze-drying is commonly used to stabilize lactic acid bacteria. Many factors have been reported to influence freeze-drying survival, including bacterial species, cell density, lyoprotectant, freezing rate, and other process parameters. Lactobacillus coryniformis Si3 has broad antifungal activity and a potential use as a food and feed biopreservative. This strain is considered more stress sensitive, with a low freeze-drying survival, compared to other commercialized antifungal lactic acid bacterial strains. We used a response surface methodology to evaluate the effects of varying sucrose concentration, cell density and freezing rate on Lb. coryniformis Si3 freeze-drying survival. The water activity of the dry product, as well as selected thermophysical properties of importance for freeze-drying; degree of water crystallization and the glass transition temperature of the maximally freeze concentrated amorphous phase (Tg) were determined. The survival of Lb. coryniformis Si3 varied from less than 6 to over 70% between the different conditions. All the factors studied influenced freeze-drying survival and the most important factor for survival is the freezing rate, with an optimum at 2.8°C/min. We found a co-dependency between freezing rate and formulation ingredients, indicating a complex system and the need to use statistical tools to detect important interactions. The degree of water crystallization decreased and the final water activity increased as a function of sucrose concentration. The degree of water crystallization and Tg was not affected by the addition of 10^(8)-10^(10) CFU/ml. At 10^(11) CFU/ml, these thermophysical values decreased possibly due to increased amounts of cell-associated unfrozen water. [Reprinted with permission from Elsevier. Copyright, 2006].

Details

  • Original title: Freeze-drying of Lactobacillus coryniformis Si3-effects of sucrose concentration, cell density, and freezing rate on cell survival and thermophysical properties.
  • Record ID : 2006-3224
  • Languages: English
  • Source: Cryobiology - vol. 53 - n. 1
  • Publication date: 2006/08

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