Frédéric Peyrin

In Vitro Colonization of the Muscle Extracellular Matrix Components by Escherichia coli O157:H7: The Influence of Growth Medium, Temperature and pH on Initial Adhesion and Induction of Biofilm Formation by Collagens I and III

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 are responsible for repeated food-poisoning cases often caused by contaminated burgers. EHEC infection is predominantly a pediatric illness, which can lead to life-threatening diseases. Ruminants are the main natural reservoir for EHEC and food contamination almost always originates from faecal contamination. In beef meat products, primary bacterial contamination occurs at the dehiding stage of slaughtering. The extracellular matrix (ECM) is the most exposed part of the skeletal muscles in beef carcasses. Investigating the adhesion to the main muscle fibrous ECM proteins, insoluble fibronectin, collagen I, III and IV, laminin-α2 and elastin, results demonstrated that the preceding growth conditions had a great influence on subsequent bacterial attachment. In the tested experimental conditions, maximal adhesion to fibril-forming collagens I or III occurred at 25°C and pH 7. Once initially adhered, exposure to lower temperatures, as applied to meat during cutting and storage, or acidification, as in the course of post-mortem physiological modifications of muscle, had no effect on detachment, except at pHu. In addition, dense biofilm formation occurred on immobilized collagen I or III and was induced in growth medium supplemented with collagen I in solution. From this first comprehensive investigation of EHEC adhesion to ECM proteins with respect to muscle biology and meat processing, new research directions for the development of innovative practices to minimize the risk of meat contamination are further discussed.

In situ thermal denaturation of myofibre sub-type proteins studied by immunohistofluorescence and synchrotron radiation FT-IR microspectroscopy.

The thermal denaturation of proteins in skeletal muscle was studied and characterised for the first time taking into account the in situ metabolic and contractile fibre types. From serial histological sections, collagen, elastin, various type I, IIa and IIx fibres and type I-IIa and IIa-IIx hybrids were identified by immunohistofluorescence. Histological sections were incubated in buffer solutions at increasing temperatures (40, 50, 60, 70 and 80°C). Protein secondary structure was investigated by synchrotron radiation FT-IR microspectroscopy on connective tissue and in muscle fibres rigorously identified for sub-type. Whatever the target protein components, increasing temperature resulted in a decrease in α-helix secondary structure and an increase in β-sheet structure. This phenomenon was more pronounced for intracellular proteins than for connective tissue. Although hybrid fibres were generally somewhat less sensitive to unfolding than the pure types, the amplitude of the thermal denaturation of intracellular proteins was practically independent of fibre type.

Effect of turbulent integral length scale on heat transfer around a circular cylinder placed cross to an air flow

Abstract The effect of air turbulence on heat transfer around a cylinder is known to be dramatic. Relations based on the intensity of turbulence have been developed to take it into account. However the range of validity of these relations is under debate since they do not take into consideration the scale of turbulence which should also have an effect. This debate is not only theoretical because if the turbulent length scale is important most experiments usually performed at the laboratory scale would probably be disputable in practical conditions. This paper aims at providing some experimental arguments on the effect of the turbulent length scale on the average transfer coefficient value. The effect of a twofold multiplication of this scale from 0.05 to 0.10 m on the heat transfer coefficient has been measured around a circular cylinder placed in the cross-flow of air whose free stream turbulence intensity was 14%. In this range, the effect of the turbulent integral length scale on the average transfer coefficient value is very small and cannot be compared with the dramatic influence of the turbulence intensity.

Frontal UV–visible fluorescence polarization measurement for bovine meat ageing assessment

Among the techniques based on light interactions with biological tissues, fluorescence polarization offers a selective means of characterizing the organization of biological tissues. This paper presents a methodology for investigating the fluorescence polarization of muscle tissues in to obtain structural information, and specifically the structural modifications caused by meat ageing. A theoretical model of fluorescence anisotropy based on geometrical distribution and properties of tryptophan, the major fluorophore in muscle tissues, is proposed. Experimental data are fitted with the model and fitting parameters (C(1), C(2) and τ) are tracked during meat ageing. Results presented demonstrate how the method is able to show muscle structure modification during ageing. They highlight changes in structural proteins along the main axis of myofibrils and changes in the tryptophan environment resulting from the physicochemical and enzymatic processes at work during ageing.

Protein Matrix Involved in the Lipid Retention of Foie Gras during Cooking: A Multimodal Hyperspectral Imaging Study

Denaturation of the protein matrix during heat treatment of duck foie gras was studied in relationship to the amount of fat loss during cooking. A low fat loss group was compared with a high fat loss group by histochemistry, FT-IR, and synchrotron UV microspectroscopy combination to characterize their protein matrix at different scales. After cooking, the high fat loss group showed higher densification of its matrix, higher ultraviolet tyrosine autofluorescence, and an infrared shift of the amide I band. These results revealed a higher level of protein denaturation and aggregation during cooking in high fat loss than in low fat loss foie gras. In addition, the fluorescence and infrared responses of the raw tissue revealed differences according to the level of fat losses after cooking. These findings highlight the importance of the supramolecular state of the protein matrix in determining the fat loss of foie gras.

Sarcomere length determination using front-face fluorescence polarization.

Tryptophan is the major intrinsic fluorophore in muscle and is a constituent of proteins that have two preferential alignments both parallel and perpendicular to muscle fibre direction. A simple theoretical model and an experimental method based on front-face fluorescence polarization technique for tryptophan fluorescence anisotropy measurements were used for the estimation of post-rigor sarcomere length in beef in the range 1.6-3.4μm. Fluorescence anisotropy and structure-related model variables displayed changes in cold-shortened samples compared with normal and stretched ones. The anisotropy of contracted samples was lowered by misalignment of fibres in the sample. This method can therefore be used for in-line detection of cold shortening which has meat toughness as a consequence.

Polarized front-face fluorescence for muscle tissue structure evaluation

The fluorescence anisotropy of a rigid medium is a consequence of photoselection of fluorophores and their orientations. This makes it possible to use polarized front-face fluorescence to provide structural information on biological tissues like muscle. Tryptophan is the major intrinsic fluorophore in muscle. It is embedded in proteins which act as building blocks for muscle structuration because of their preferential alignment. Our working hypothesis is that when the arrangement of the proteins changes, there are concomitant changes in fluorescence anisotropy parameters. Our research is directed toward evaluating muscle structure and its evolution post mortem. We report a theoretical simple model of tryptophan fluorescence and an experimental method to measure the fluorescence anisotropy of biological opaque tissues. Instrumental and optical considerations have to be taken into account in experiments on front-face polarization to make certain of measurement accuracy. Therefore, we present a detailed report on the adjustments and corrections made on a conventional L-spectrofluorimeter to adapt it to fluorescence anisotropy measurements on biological tissues. Data from several experiments demonstrate how the method is able to show muscle structure modifications. We show how it is possible to fit experimental data with the model developed in order to obtain structural information.

Relationship between histochemical, structural characteristics and oxidative stability of rhea limb muscles

Histochemical and structural characteristics were investigated in Gastrocnemius pars interna (GN) and Iliofiburalis (IF) limb muscles of Rhea americana. The average myofibre area cross-section was greater in GN than IF muscle (p<0.001), whereas the fibre density per section was higher in IF than GN muscle. The only type of myofibre found in both the rhea limb muscles analysed in this study was fast-twitch oxidative-glycolytic fibres (FOG). Immunolabelling analysis and ultrastructural observation of myofibres confirmed the contractile and metabolic characteristics of rhea myofibres, revealing the absolute fast isoform of myosin heavy chain and the abundance of glycogen and mitochondria inside the cells, mainly in IF muscle. These findings converged with previous results on the biochemical and physicochemical characteristics of rhea meat to provide further evidence that myofibre composition substantially influences the oxidative reactions of the muscle and therefore the meat quality, but more in-depth examination is needed to establish the links between myofibre characteristics, myofibre glycogen concentration and meat stability during storage.

Sodium Chloride Diffusion during Muscle Salting Evidenced by Energy-Dispersive X-ray Spectroscopy Imaging

To better understand the relationship between the muscle structure and NaCl transfers in meat, we used energy-dispersive X-ray spectroscopy (EDS) coupled with scanning electron microscopy (SEM) to analyze brined and dry-salted rat muscles. The muscles were freeze-dried to avoid the delocalization of soluble ions that happens in regular dehydration through a graded series of ethanol. Na and Cl maps were superimposed on SEM images to combine the muscle structure and NaCl diffusion. Brining causes rapid diffusion of NaCl through the tissue. Most brine diffuses in a linear front from the muscle surface, but a small proportion enters through the perimysium network. The muscle area penetrated by brine shows heterogeneous patterns of NaCl retention, with some connective tissue islets containing more NaCl than other parts of perimysium. NaCl penetration is considerably slower after dry salting than after brining.