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Research article2006Peer reviewed

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

Schoug A, Olsson J, Carlfors J, Schnurer J, Hakansson S

Abstract

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 degrees 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/mI. At 10(11) CFU/ml, these thermophysical values decreased possibly due to increased amounts of cell-associated unfrozen water. (c) 2006 Elsevier Inc. All rights reserved

Published in

Cryobiology
2006, Volume: 53, number: 1, pages: 119-127
Publisher: ACADEMIC PRESS INC ELSEVIER SCIENCE

      SLU Authors

        • UKÄ Subject classification

        Agricultural Science
        Environmental Sciences related to Agriculture and Land-use

        Publication identifier

        DOI: https://doi.org/10.1016/j.cryobiol.2006.04.003

        Permanent link to this page (URI)

        https://res.slu.se/id/publ/8791