muramidase and n-hexadecane

The Oil Transfer Technique (OTT) was developed by Taisne et al. [1] to measure coalescence during emulsification and has been applied since in several studies. One of the main drawbacks of this technique is that it only gives a qualitative measure of coalescence. This paper proposes a new evaluation method of OTT experimental results for estimating qualitative coalescence rates, e.g. for investigating the scaling of coalescence with emulsification parameters (such as homogenizing pressure, and emulsifier concentration). The method is based on comparison with simulated OTT experiments using bivariate Population Balance Equation models. Simulations have been performed under a wide variety of conditions in order to investigate the influence of assumptions on coalescence and fragmentation kernels. These investigations show that the scaling of coalescence rates could be determined accurately when the scaling of efficient residence time of drops in the active region of homogenization is known. The proposed evaluation method is also exemplified by analyzing OTT data from two previously published studies.

Topics: Alkanes; Computer Simulation; Emulsifying Agents; Emulsions; Hydrocarbons, Brominated; Kinetics; Lactoglobulins; Models, Chemical; Muramidase; Oils; Sodium Dodecyl Sulfate; Thermodynamics; Water

The aim of the study was to evaluate the adhesion of Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus rhamnosus strain GG to saliva-coated surfaces in vitro.. Fifteen radiolabeled dairy L. delbrueckii subsp. bulgaricus strains and L. rhamnosus GG were tested for their ability to adhere to saliva-coated hydroxyapatite beads and polystyrene microtiter plates and the radioactivity was measured by liquid scintillation counter. The effects of lysozyme on the adhesion of lactobacilli and of pretreatment with lactobacilli on the adhesion of Streptococcus sanguinis were also assessed.. All strains tested adhered to saliva-coated surfaces but with significantly different binding frequencies. The adhesion of the L. delbrueckii subsp. bulgaricus strains remained lower in comparison to L. rhamnosus strain GG. One L. delbrueckii subsp. bulgaricus strain showed binding frequency comparable to S. sanguinis. Lysozyme pretreatment of the samples significantly increased lactobacillus adhesion to saliva-coated surfaces.. The present results showed significant variations in the adhesion capacity of the Lactobacillus strains studied. Adhesion to oral surfaces is of primary importance for bacterial colonization in the mouth. Only one of the L. delbrueckii subsp. bulgaricus dairy starter culture strains investigated had a high adhesion percentage. This strain might then be considered for further investigations in the oral environment.

Topics: Alkanes; Bacterial Adhesion; Biocompatible Materials; Coated Materials, Biocompatible; Dental Pellicle; Durapatite; Humans; Hydrophobic and Hydrophilic Interactions; Lacticaseibacillus rhamnosus; Lactobacillus delbrueckii; Muramidase; Polystyrenes; Probiotics; Saliva; Streptococcus; Streptococcus mutans; Surface Properties; Yogurt

Proteins adsorbed at fluid/fluid interfaces influence many phenomena: food emulsion and foam stability (Murray et al. Langmuir 2002, 18, 9476 and Borbas et al. Colloids Surf., A 2003, 213, 93), two-phase enzyme catalysis (Cascao-Pereira et al. Biotechnol. Bioeng. 2003, 83, 498; 2002, 78, 595), human lung function (Lunkenheimer et al. Colloids Surf., A 1996, 114, 199; Wustneck et al.; and Banerjee et al. 2000, 15, 14), and cell membrane mechanical properties (Mohandas et al. 1994, 23, 787). Time scales important to these phenomena are broad, necessitating an understanding of the dynamics of biological macromolecules at interfaces. We utilize interfacial shear and dilatational deformations to study the rheology of a globular protein, lysozyme, and a disordered protein, beta-casein, at the hexadecane/water interface. Linear viscoelastic properties are measured using small amplitude oscillatory flow, stress relaxation after a sudden dilatational displacement, and shear creep response to probe the rheological response over broad experimental time scales. Our studies of lysozyme and beta-casein reveal that the interfacial dissipation mechanisms are strongly coupled to changes in the protein structure upon and after adsorption. For beta-casein, the interfacial response is fluidlike in shear deformation and is dominated by interfacial viscous dissipation, particularly at low frequencies. Conversely, the dilatational response of beta-casein is dominated by diffusion dissipation at low frequencies and viscous dissipation at higher frequencies (i.e., when the experimental time scale is faster than the characteristic time for diffusion). For lysozyme in shear deformation, the adsorbed protein layer is primarily elastic with only a weak frequency dependence. Similarly, the interfacial dilatational moduli change very little with frequency. In comparison to beta-casein, the frequency response of lysozyme does not change substantially after washing the protein from the bulk solution. Apparently, it is the irreversibly adsorbed fraction that dominates the dynamic rheological response for lysozyme. Using stress relaxation after a sudden dilatational displacement and shear creep response, the characteristic time of relaxation was found to be 1000 s in both modes of deformation. The very long relaxation time for lysozyme likely results from the formation of a glassy interfacial network. This network develops at high interfacial concentrations where the molecules are highly c

Topics: Adsorption; Alkanes; Animals; Biofilms; Caseins; Cattle; Chickens; In Vitro Techniques; Membranes, Artificial; Muramidase; Pressure; Protein Conformation; Proteins; Rheology; Surface Properties; Thermodynamics; Water

Polycationic polymers have been noted for their effects in promoting cell adhesion to various surfaces, but previous studies have failed to describe a mechanism dealing with this type of adhesion. In the present study, three polycationic polymers (chitosan, poly-L-lysine, and lysozyme) were tested for their effects on microbial hydrophobicity, as determined by adhesion to hydrocarbon and polystyrene. Test strains (Escherichia coli, Candida albicans, and a nonhydrophobic mutant, MR-481, derived from Acinetobacter calcoaceticus RAG-1) were vortexed with hexadecane in the presence of the various polycations, and the extent of adhesion was measured turbidimetrically. Adhesion of all three test strains rose from near zero values to over 90% in the presence of low concentrations of chitosan (125 to 250 micrograms/ml). Adhesion occurred by adsorption of chitosan directly to the cell surface, since E. coli cells preincubated in the presence of the polymer were highly adherent, whereas hexadecane droplets pretreated with chitosan were subsequently unable to bind untreated cells. Inorganic cations (Na+, Mg2+) inhibited the chitosan-mediated adhesion of E. coli to hexadecane, presumably by interfering with the electrostatic interactions responsible for adsorption of the polymer to the bacterial surface. Chitosan similarly promoted E. coli adhesion to polystyrene at concentrations slightly higher than those which mediated adhesion to hexadecane. Poly-L-lysine also promoted microbial adhesion to hexadecane, although at concentrations somewhat higher than those observed for chitosan. In order to study the effect of the cationic protein lysozyme, adhesion was studied at 0 degree C (to prevent enzymatic activity), using n-octane as the test hydrocarbon. Adhesion of E. coli increased by 70% in the presence of 80 micrograms of lysozyme per ml. When the negatively charged carboxylate residues on the E. coli cell surface were substituted for positively charged ammonium groups, the resulting cells became highly hydrophobic, even in the absence of polycations. The observed "hydrophobicity" of the microbial cells in the presence of polycations is thus probably due to a loss of surface electronegativity. The data suggest that enhancement of hydrophobicity by polycationic polymers is a general phenomenon.

Topics: Acinetobacter; Alkanes; Bacterial Adhesion; Candida albicans; Cations; Cell Membrane; Chitin; Chitosan; Escherichia coli; Kinetics; Muramidase; Osmolar Concentration; Polylysine; Polystyrenes

Lipopolysaccharide-rich vesicles were released from Acinetobacter calcoaceticus 69V during growth on hexadecane. Vesicle formation occurred over the whole surface of the cell as demonstrated by scanning electron microscopy. In contrast, the surface of acetate-grown cells, for which little lipopolysaccharide was found in the growth medium, appeared smooth. The overall chemical composition as well as the protein and phospholipid composition of the outer membranes of both cell types was very similar. In the vesicles all outer membrane proteins were found with the exception of an Mr 10,000 polypeptide corresponding to Braun's lipoprotein. Compared with the outer membrane, the vesicles contained more phosphatidylethanolamine. Hexadecane-grown cells were susceptible to exogenously added phospholipase. Nevertheless the barrier function towards lysozyme was retained.

Topics: Acinetobacter; Alkanes; Bacterial Outer Membrane Proteins; Cell Membrane; Culture Media; Lipopolysaccharides; Microscopy, Electron, Scanning; Muramidase; Phospholipids

A method is proposed for the relatively simple and rapid separation of amphipathic biopolymers, based on adsorption onto and desorption from the surface of hexadecane droplets. Adsorption to the hexadecane:water interface was carried out by mixing hexadecane with aqueous protein solutions at room temperature. Desorption was performed by consecutive solidification and melting of the liquid hydrocarbon (m.p. 18 degrees C), resulting in coalescence of the droplets and reappearance of the desorbed moiety in the bulk aqueous phase. Of interest was the observation that lysozyme remains enzymatically active following this procedure.

Topics: Adsorption; Alkanes; Animals; Chickens; Humans; Muramidase; Proteins; Saliva; Solubility; Structure-Activity Relationship; Temperature; Water