Reducing the environmental impact of hygiene procedures in refrigerated food processing plants through optimal use of air drying – EcoSec

In order to determine the ability of Listeria monocytogenes to withstand hydric stress, a dehydration protocol in a hyperosmotic medium was developed. For further work in conditions close to those prevailing in food premises, we investigated whether the soiling materials could be replaced by more standardized laboratory media. Soils and media were compared in terms of growth, structure and adhesion forces of populations grown on stainless steel. Finally, the feasibility of using a poorly cleanable material (therefore likely to allow for persistence of the bacteria) was verified and the reproducibility of weakly and strongly adherent bacterial populations was assessed.
The numerical modeling undertaken to predict the climatic conditions surrounding the bacteria on the surfaces of a processing room requires validation at the laboratory and industrial scales. For this purpose, a test cell is currently developed for measuring the velocity, humidity and air temperature close to a wet wall and the kinetics of evaporation of water from the wall. Similar measurements are carried out in the selected industrial workshop. The kinetics of evaporation of water from a wet surface under different conditions is studied to include this process in numerical models. The energy optimization of air dehumidification is addressed by studying the use of liquid desiccants and finding equations for describing the liquid / vapor equilibrium.

The development of the dehydration protocol was performed on Listeria innocua, avirulent model for L. monocytogenes. High resistance to osmotic stress was observed, comparable to the one of organisms highly adapted to this stress such as the yeast Saccharomyces cerevisiae.
Two soils were tested, smoked salmon juice and beef exudate. The first one appears to be replaceable by a modified laboratory culture medium. In the presence of meat exudate, cells of L. monocytogenes adhering after growth formed aggregates of elongated cells while in the modified laboratory media they had normal size and adhered as single cells. A ceramic tile with many small crevices on its surface proved to retain reproducibly ten times more L. monocytogenes cells than a smooth ceramic tile. Difficult-to-remove cells, likely those placed in crevices, are in a better physiological state after contact with cleaning agents than easy-to-remove cells. A numerical tool for predicting air characteristics (speed, temperature, humidity) in a processing room is being developed. The equations of Condé-Petit (2009), which provide access to a large range of vapor concentration, temperature and partial pressure, are used in this study. They predict the relative humidity as a function of the concentration of CaCl2 and temperature, at the application step (low temperature in the workroom that has to be dried) and the regeneration step (high temperature in the equipment).

The project is progressing according to the initial work program. As Listeria is highly resistant to osmotic stress, it is necessary to understand the genetic and structural bases that allow resistance. It will also be necessary to modify the speed and amplitude conditions of the dehydration stress to find those that favor the destruction of the bacteria. To place L. monocytogenes in field conditions, we will seek non-pathogenic bacterial species likely to persist and have a favorable effect on the adhesion of L. monocytogenes. Concerning air drying, the parameters for another usual salt (LiBr) will be determined. A model describing the behavior of the two solutions in the air processing equipment will be developed. It will allow comparison to other possible techniques (desiccant wheel, mechanical cooling).

No production for the moment.

Cleaning and disinfection (C&D) are among the most important hazard control measures in ready-to-eat food plants. However, these procedures require large amounts of water and generate huge volumes of sewage with high loads of cleaning agents and biocides. More sustainable C&D strategies are therefore needed. Several food business operators have already noted the positive effects of adding an air-drying step after C&D to dry surfaces and thus control growth of microorganisms that are not detached from surfaces. However, air drying is applied empirically and no attempts have been made to define optimal air drying conditions, which would increase the efficiency of lethal hydric stress.
The purpose of the present interdisciplinary project, which gathers seven partners including three private companies, is to define optimal air drying conditions in terms of lethal impact on bacteria, sustainability of various air-drying techniques and the distribution of relative humidity, temperature and air velocity in a food processing room. The project will assess whether optimal air-drying conditions can promote the use of environmentally friendly C&D products, decrease disinfection frequency — and thus sewage volume and biocide release into the environment, without affecting, and even improving, food safety and occupational health.
Fundamental knowledge on the impact of hydric stress on bacterial death, inactivation, resistance, and adaptation will be produced from experiments conducted on a selected pathogenic bacterium or its surrogate. This will be done to better understand the mechanisms involved and to design a tool to detect non-culturable, stress-adapted cells. Models will be constructed to predict: (1) the distribution of relative-humidity, temperature and air velocity in a food processing room; (2) the energy consumption attributable to the control of air humidity according to the drying technique; (3) the persistence potential of the selected pathogenic bacteria. These models, after validation, will be used to determine the most influential factors and recommendations will be issued on how to reach the lowest microbial load on solid surfaces with the lowest environmental impact.