Christine Faille

Identification of surface characteristics relevant to the hygienic status of stainless steel for the food industry

Abstract The hygienic status of stainless steels used for food equipment was investigated by means of the number of residual adhering Bacillus cereus spores after a complete run of soiling and cleaning in place procedure. The 14 materials tested (304, 316 and 430 grades; pickling (2B), bright annealed (2R), and electropolished finishes) were shown to be highly hygienic with slight differences in the number of residual adhering spores. Nevertheless, they could be grouped into different classes according to their hygienic status. Grade, and to a lesser extent finish, were found to be related to the hygienic status. Among the stainless steel surface free energies, only γ + could be slightly related to the hygienic character. Moreover, surface topography by means of the R PK parameter, corresponding to the height of the top portion of the surface profile, was also shown to control the hygiene of stainless steel surfaces.

Cleaning in place: effect of local wall shear stress variation on bacterial removal from stainless steel equipment

Local wall shears stress analysis as well as cleanability experiments on di!erent pieces of equipment in various circuit arrangements were performed. Pieces of equipment used in this work, stainless steel made, were representative of production lines:straight pipes of di!erent diameters, sudden or gradual contraction or expansion pipes. Local wall shear stress values, obtained by an electrochemical method, were shown to be in9uenced by the loop arrangement. Geometry as the gradual expansion pipe had an e!ect on the upstream straight pipe where the wall shear stress values were two times lower than in other con:gurations as with a sudden expansion. In sudden geometry, the bacterial removal during cleaning was improved by the increase of the 9ow rate, corresponding to the increase of the mean local wall shear stress. However, in gradual expansion or contraction pipe, cleanability was not improved by the increase of 9ow rate. The e!ect of the mean wall shear stress on the removal has been con:rmed. Moreover, this work demonstrated a clear positive e!ect of an increase of the 9uctuation rate on the spore detachment. Low mean wall shear stress zones as in sudden expansion (around 0:15 Pa) could be cleanable because of the high 9uctuation rate (around 21%). These results underline the importance of the design and the 9ow con:guration. ? 2002 Elsevier Science Ltd. All rights reserved.

Using enzymes to remove biofilms of bacterial isolates sampled in the food-industry

The aim of this study was to analyze the cleaning efficiency of polysaccharidases and proteolytic enzymes against biofilms of bacterial species found in food industry processing lines and to study enzyme effects on the composition of extracellular polymeric substances (EPS) and biofilm removal in a Clean-in-Place (CIP) procedure. The screening of 7 proteases and polysaccharidases for removal of biofilms of 16 bacterial species was first evaluated using a microtiter plate assay. The alkaline pH buffer removed more biofilm biomass as well as affecting a larger range of bacterial species. The two serine proteases and α-amylase were the most efficient enzymes. Proteolytic enzymes promoted biofilm removal of a larger range of bacterial species than polysaccharidases. Using three isolates derived from two bacterial species widely found in food processing lines (Pseudomonas fluorescens and the Bacillus cereus group), biofilms were developed on stainless steel slides and enzymatic solutions were used to remove the biofilms using CIP procedure. Serine proteases were more efficient in removing cells of Bacillus biofilms than polysaccharidases. However, polysaccharidases were more efficient in removing P. fluorescens biofilms than serine proteases. Solubilization of enzymes with a buffer containing surfactants, and dispersing and chelating agents enhanced the efficiency of polysaccharidases and proteases respectively in removing biofilms of Bacillus and P. fluorescens. A combination of enzymes targeting several components of EPS, surfactants, dispersing and chelating agents would be an efficient alternative to chemical cleaning agents.

Potential occurrence of adhering living Bacillus spores in milk product processing lines

C. FAILLE, F. FONTAINE AND T. BÉNÉZECH. 2001.

Growth, morphology and surface properties of Listeria monocytogenes Scott A and LO28 under saline and acid environments

Aims: The effect of salt and acid on the growth and surface properties of two strains of Listeria monocytogenes was investigated.

Biofilm formation and cell surface properties among pathogenic and nonpathogenic strains of the Bacillus cereus group.

ABSTRACT Biofilm formation by 102 Bacillus cereus and B. thuringiensis strains was determined. Strains isolated from soil or involved in digestive tract infections were efficient biofilm formers, whereas strains isolated from other diseases were poor biofilm formers. Cell surface hydrophobicity, the presence of an S layer, and adhesion to epithelial cells were also examined.

Comparative evaluation of adhesion, surface properties, and surface protein composition of Listeria monocytogenes strains after cultivation at constant pH of 5 and 7

Aims:  To analyse the cellular mechanisms that influence Listeria monocytogenes adhesion onto inert surfaces under acidic growth conditions.

Occurrence of Bacillus cereus Spores with a Damaged Exosporium: Consequences on the Spore Adhesion on Surfaces of Food Processing Lines

This study was designed to evaluate the occurrence of Bacillus cereus spores with a damaged exosporium and the consequences of such damages on spore adhesion. The analysis of nine strains sporulated under optimal conditions (Spo8-agar, 30 degrees C) revealed that damaged exosporia were systematically found in one strain (B. cereus D17) and occasionally in two others (B. cereus ATCC 14579T and B. cereus D6). The prevalence of spores with damaged exosporia increased when sporulation occurred under less favorable conditions (Spo8-broth or high temperature); for example, more than 50% of the B. cereus ATCC 14579T spores were damaged when sporulation occurred at 40 degrees C on Spo8-agar or at 30 degrees C in Spo8-broth. Furthermore, when subjected to shear stresses by circulation of spore suspensions through a peristaltic pump, the exosporium of a significant amount of spores became partially or totally shorn off (for example, 40% of the B. cereus ATCC 14579T spores). The ability of damaged spores to adhere to inert surfaces and to resist cleaning under shear stress was significantly affected when compared with intact spores, resulting in a decreased number of adhering spores (P < or = 0.004) and enhanced resistance to cleaning (P < or = 0.008). This study provides evidence that, under various conditions, the exosporium of B. cereus spores can be partly or wholly damaged, thereby affecting the ability of spores to contaminate the surfaces of food processing lines. The presence of spores devoid of exosporium will be of importance in determining the risk associated with B. cereus spores adherent to food processing line surfaces.

Cleaning-in-Place: Modelling of Cleaning Kinetics of Pipes Soiled by Bacillus Spores Assuming a Process Combining Removal and Deposition

In food industries, thorough cleaning -in-place procedures for the unheated surfaces of food processing equipment are required to ensure the safety of food products by the removal of microorganisms. The aim of this work is to model the removal kinetics of Bacillus spores during a cleaning-in-place procedure. These spores were chosen for their occurrence in dairies. The removal of Bacillus cereus spores was found to be strongly dependent on both chemical action (sodium hydroxide), which lowers the adhesion strength of spores onto hard surfaces, and hydrodynamic conditions during cleaning through wall shear stress. A simple model (first-order reaction) assuming a process combining removal and deposition during cleaning was detailed and experimentally confirmed. In addition, a significant effect on the effective removal rate constant by both the flow conditions applied during the soiling procedure and applied during cleaning was observed.

Morphology and physico-chemical properties of Bacillus spores surrounded or not with an exosporium: consequences on their ability to adhere to stainless steel.

This study was designed to elucidate the influence of spore properties such as the presence of an exosporium, on their ability to adhere to materials. This analysis was performed on 17 strains belonging to the B. cereus group and to less related Bacillus species. We first demonstrated that spores of the B. cereus group, surrounded by an exosporium, differed in their morphological features such as exosporium size, number of appendages or hair-like nap length. We also found that the saccharidic composition of exosporium differed among strains, e.g. concerning a newly identified rhamnose derivative: the 2,4-O-dimethyl-rhamnose. Conversely, spores of distant Bacillus species shared morphological and physico-chemical properties with B. cereus spores. Some external features were also observed on these spores, such as a thin loose-fitting layer, whose nature is still to be determined, or a thick saccharidic layer (mainly composed of rhamnose and quinovose). The ability of spores to adhere to stainless steel varied among strains, those belonging to the B. cereus group generally being the most adherent. However, the presence of an exosporium is not sufficient to explain the ability of spores to adhere to inanimate surfaces. Indeed, when the 17 strains were compared, hydrophobicity and the number of appendages were the only significant adhesion parameters. Furthermore, the differences in spore adhesion observed within the B. cereus group were related to differences in the number of appendages, the exosporium length and to a lesser extent, the zeta potential.