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Stabilization of frozen Lactobacillus bulgaricus suspensions: interactions between cryoprotectants, freezing rates and storage temperature

Abstract : Improvement of the cryopreservation protocols of lactic acid bacteria (LAB) need to identify and control the principal factors responsible for cellular cryoinjury. An experimental design allowed us quantify the effects on Lactobacillus delbrueckii subsp. bulgaricus CFL1 of two cryoprotective agents (glycerol or maltodextrin), three freezing protocols (controlled nucleation at )5C followed by a cooling rate of 5 C /min or 2500 C/min, or direct immersion in liquid nitrogen), and two storage temperatures 20,80 C. Samples were frozen in 0.5 ml capacity straws. The LAB acidification activity was determined before and after the freezing and after 1 month of frozen storage by using the CINAC system. Fractured straws were examined following each freezing condition using the cryostage of a scanning electron microscope (CryoSEM) and by freeze substitution. Straws were also examined following storage at 20 C. The acidification activity of L. bulgaricus decreased after freezing (whatever the kinetics) and also during one-month storage at 20 C. Whatever the cryoprotectant used, resistance to freezing was improved by direct immersion in liquid nitrogen. When applying a controlled nucleation during freezing at 5 C, the acidification activity was also found to be higher for the higher cooling rate (2500 C/min). Considering interaction between factors, the detrimental effect of storage at 20 C was attenuated by an adequate combination of the cryoprotectant (glycerol) and cooling rate (nucleation followed by a low cooling rate of 5 C/min). But, immersion in liquid nitrogen and no additive remained better if storing at 80 C. The LAB acidification activity was related to the ice crystal size and distribution in the frozen samples, as well as the bacterial location in the heterogeneous frozen material.
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https://hal.inrae.fr/hal-02759750
Déposant : Migration Prodinra <>
Soumis le : jeudi 4 juin 2020 - 04:40:18
Dernière modification le : samedi 27 juin 2020 - 19:44:07

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Fernanda Fonseca, Michèle Marin, G. J. Morris. Stabilization of frozen Lactobacillus bulgaricus suspensions: interactions between cryoprotectants, freezing rates and storage temperature. 41. Annual Meeting of the Society for Cryobiology, Jul 2004, Bejing, China. ⟨10.1016/j.cryobiol.2004.10.001⟩. ⟨hal-02759750⟩

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