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Cryopreservation of Lactobacillus delbrueckii subsp. bulgaricus: towards a quantitative understanding of the cell biophysical response during freezing

Abstract : Concentrates of lactic acid bacteria are widely used for dairy fermentation processes to produce cheeses, yoghurts and dairy products with health benefits. Freezing and storage at low temperatures (<40 C) are commonly applied to preserve the viability of concentrates while maintaining their technological properties (acidification activity, production of aroma compounds and contribution to product texture) but cause significant cell injury and death. Recent studies demonstrated that formation of intracellular ice does not occur during freezing of Lactobacillus delbrueckii subsp. bulgaricus [2] and cell injury is mainly caused by cellular dehydration. Our objective was to investigate and quantify the water transport processes and the physiological injuries due to cell dehydration. Two complimentary approaches were developed to investigate cell dehydration. Firstly, suspensions of bacteria were submitted to osmotic stress by increasing rapidly or slowly the concentration on a non penetrating solute (sucrose). The response of the cells to hydric perturbations was analyzed by measuring the changes in cell volume by Coulter technique and in cell size by optical microscopy and was related to the corresponding physiological state. Secondly, preliminary experiments using the differential scanning calorimetric technique developed by Devireddy et al. [1] were performed in order to obtain data of the cell volume change during freezing. This DSC method appears to be more relevant than cryomicroscopic techniques for studying water transport during the freezing of small and non spherical cells. The biophysical parameters of water transport were estimated from both the DSC data and the osmotic dehydration experiments. The physiological response of Lactobacillus delbrueckii subsp. bulgaricus was compared to the bacterial dehydration response at different cooling rates.
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Submitted on : Wednesday, June 3, 2020 - 9:28:43 PM
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Stéphanie Passot, Aline Rault, Stéphanie Cenard, Fernanda Fonseca. Cryopreservation of Lactobacillus delbrueckii subsp. bulgaricus: towards a quantitative understanding of the cell biophysical response during freezing. 47. Annual Meeting of the Society for Cryobiology, Jul 2010, Bristol, United Kingdom. ⟨10.1016/j.cryobiol.2010.10.039⟩. ⟨hal-02755152⟩

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