Experimental study and optimization of freeze-drying cycles of a model Casei type probiotic bacteria

Abstract

The objective of this paper was to present experimental results concerning the optimization of freeze-drying cycles of a model type casei probiotic bacteria with water based formulations using lactose and polymer (PVP) as cryo/lyo protectants. First, we investigated the influence of different formulations and of different freezing protocols (freezing rates and pre-freezing treatment) on the viability of the model probiotic strain after the freezing step. Secondly, the heat transfer coefficient was characterized by an overall heat transfer coefficient determined with pure water. In our very soft operating conditions - total gas pressure from 10 to 30 Pa and shelf temperature from −20 °C to 10 °C – the sublimation process was mainly controlled by the heat transfer from the vial surroundings to the sublimation front that take place by conduction, by contact at the vial bottom and by radiation from the self and from the chamber walls. Next, as concern the single freeze-drying process approach, with the preselected formulation - composition and freezing rate - we studied the influence of the sublimation operating parameters, namely the total gas pressure inside the sublimation chamber and the shelf temperature on the bacteria survival ratios and on the sublimation times. In agreement with previous literature data, we observed that the sublimation rate increased with the increasing total gas pressure and the shelf temperature. It is worth to note that these experimental data have shown that sublimation times could be reduced by about 40% without reducing the bacteria viability by realizing the sublimation at temperatures slightly higher (about 4 °C) than the classical limit temperatures encountered during the freeze-drying processes of thermosensible biological systems like vaccines i.e., the vitreous transition temperatures of the formulations.

Keywords:

• Formulation
• freezing
• freeze-drying
• sublimation times
• probiotics
• Lactobacillus Casei

Additional information

Notes on contributors

Pierre Verlhac

Pierre Verlhac completed his PhD in Process Engineering through the Université Claude Bernard Lyon 1. He focuses his research on the freeze-drying of probiotics and has presented his research at conferences in France and Spain. He is currently employed as Pharmaceutical Process Specialist in drug delivery systems in Lonza, Strasbourg.

Séverine Vessot-Crastes is Professor of Chemical Engineering at the Université Claude Bernard Lyon 1 (France) in the CNRS laboratory called LAGEPP (UMR 5007). She is working on the domain of pharmaceutical products (vaccines, proteins, probiotics, etc.) freeze-drying process study and optimisation with many industrial partnerships (Sanofi, Pfizer, etc.).

Claudia Cogné's activities focus on freezing process concerning the control of the nucleation step and ice crystal growth. Studies are developed both with an experimental and a numerical approach.

Julien Andrieu is presently Emeritus Professor of Chemical Engineering at the Université Claude Bernard Lyon 1 (France) in the CNRS laboratory called LAGEPP (UMR 5007). He is working on the domain of pharmaceutical products (vaccines, proteins, probiotics, etc.) freeze-drying process study and optimisation with many industrial partnerships (Sanofi, Pfizer, etc.). He is co-author of 218 revised full papers, namely 100 peer reviewed papers in Food or Pharmaceutical or Chemical Engineering International Scientific Journals and 118 revised full papers in International Congress Proceedings. More than 1700 total quotations. Factor H = 24 (May 2019).

Laurent Beney is Professor of Food Process Engineering at AgroSup Dijon. He is the director of the laboratory “Procédés Alimentaires et Microbiologiques” which gathers 60 permanent researchers and 50 PhD students. He studies the effects of environmental variables on microorganisms aiming the development of efficient long term preservation processes of ferments and probiotics.

Patrick Gervais is Emeritus Professor of Process Engineering at AgroSup Dijon. Founder of the laboratory “Procédés Alimentaires et Microbiologiques, his research concerns the effects of environmental parameters on microorganisms aiming to an improved destruction of pathogens or to an improved preservation of ferments and probiotics.