Modelisation de la thixotropie d'une solution de carboxymethylcellulose et de silicate d'aluminium

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Modelisation de la thixotropie d'une solution de carboxymethylcellulose et de silicate d'aluminium

National audienc

Cleanabilty study of a Scraped Surface Heat Exchanger

International audienceScraped Surface Heat Exchangers (Contherm SSHE model 6 x 3) are widely used industrially. In this kind of heat exchanger, the inlet and the outlet are difficult to clean due to their particular geometry and the presence of seals. A specific study was conducted on the inlet bowl of a SSHE, whose design has been optimized by the manufacturer in order to minimize risk of deposition by eliminating hydrodynamic dead zones. For this purpose, measurements of wall shear stress were made by an electrochemical method, for different hydrodynamic conditions. On the other hand, cleanability measurements were also performed. The bowl geometry tested presented no dead zones. However, the available space for flow significantly reduces the Reynolds number and turbulence intensity. As a consequence, three areas of increasing contamination appeared throughout the bowl due to the low mean and fluctuating shear stress values. The use of a pulsating flow increases these fluctuations, and thereby reduces the residual contamination. (C) 2012 The Institution of Chemical Engineers

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

International audienceAIMS: To analyse the cellular mechanisms that influence Listeria monocytogenes adhesion onto inert surfaces under acidic growth conditions. METHODS AND RESULTS: The adhesion capability of all the strains was significantly reduced after cultivation at constant pH 5 than at constant pH 7 and the cell surface was significantly less hydrophobic at pH 5 than at 7. At pH 5, the analyses of surface protein composition revealed that the flagellin was downregulated for all strains, which was confirmed by the absence of flagella and the P60 protein was upregulated for L. monocytogenes EGD-e, X-Li-mo 500 and 111. The use of L. monocytogenes EGD mutants revealed that flagellin could be involved in the adhesion process, but not P60 protein. It was also observed that the hydrophobic character was not linked to the presence or the absence of flagellin or P60 protein at the cell surface of L. monocytogenes. CONCLUSIONS: The decrease of L. monocytogenes adhesion at pH 5 could be attributed to the downregulation of the flagellin synthesis under the acidic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Conservation of food product at pH 5 will delay bacterial adhesion and biofilm formation during food processing on inert surfaces when the product is contaminated with L. monocytogenes

Cell adhesion and related fouling mechanism on a tubular ceramic microfiltration membrane using Bacillus cereus spores

International audienceAdhesion of microorganisms to the membrane surface is an important and critical first step in biofilm fouling. Fouling mechanisms governing the adhesion of Bacillus cereus spores on a 0.45 mu m tubular ceramic microfiltration membrane together with the relationship between hydraulic and microbiological cleanliness were investigated. Hydraulic cleanliness was evaluated using three parameters: percent flux recovery (FR), percent reversible removed fouling (RF) and a hydraulic cleanliness criterion (HCC). Microbiological cleanliness was assessed from the residual microbial population onto the membrane surface remaining after the fouling-rinsing sequence. The residual contamination (median value equal to 5.2 log cfu cm(-2) for the whole set of experiments) was found to be uniform along the membrane path. Flux versus time curves supported the intermediate blocking filtration law at the initial stages of fouling during which microfiltration behaves as a dead-end filtration. Under fixed hydrodynamic shear conditions and solution chemistry (pH, ionic strength), cell - membrane adhesion was shown to be predominantly controlled by the permeation drag force. The residual contamination level could be predicted by means of a linear relationship involving two independent variables derived from fouling data: the blocked area per unit filtrate volume associated with the intermediate blocking filtration law (sigma) and a fouling parameter (noted F-y). A correlation was found between the residual spore population (median log N) and the residual irreversible fouling resistance. FR appeared to be a good indicator of microbiological cleanliness. A calculation using the actual shape of Bacillus cereus spores appeared to partly explain the discrepancies observed between the predicted and observed normalized flux decline following rinsing. This emphasized the large fouling capability of adhered bacteria, which resulted in the substantial water flux declines left after rinsing

Des progres scientifiques et techniques dans la conception des echangeurs de chaleur a surface raclee

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Conception hygiénique de matériel et nettoyage-désinfection pour une meilleure sécurité en industrie agroalimentaire

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Influence des contraintes de cisaillement sur la nettoyabilité des équipements

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Viability and surface properties of spores subjected to a cleaning-in-place procedure: consequences on their ability to contaminate surfaces of equipment

International audienceThis study was designed to evaluate how conditions encountered by spores during cleaning-in-place (CIP) procedures affected their surface properties, their viability and ability to contaminate materials. Spores from five Bacillus cereus strains were treated with NaOH at high temperature. Results revealed that high temperatures (exceeding 60 degrees C) and NaOH concentrations (over 0.5%) were required to significantly decrease spore viability (3-5 log decrease). In these conditions, modifications were also clearly observed by microscopy to various surface structures of spores (appendages, exosporium, and especially to the hair-like nap) but also to their coat. Therefore, the ability of culturable spores to adhere decreased for the majority of strains tested. We then demonstrated that spores in suspension in NaOH could adhere to surfaces of a CIP rig and that the contamination level was controlled by flow pattern. Consequently, re-adhesion along the processing line might occur during CIP procedures and this phenomenon must be taken into account when defining cleaning strategies