The Effect of Serial Passaging of Lactobacilli in Liquid Medium on their Physico-Chemical and Structural Surface Characteristics

The aim of this study was to examine the effect of serial passaging in liquid medium on physico-chemical and structural surface characteristics of two lactobacillus strains. To this end, starting cultures (p = 1) of urogenital isolate L. acidophilus RC 14 and poultry isolate L. fermentum B54 were serially passaged in liquid medium up to 20 times (p = 20). In both strains, similar physico-chemical and structural changes were observed following serial passaging. According to water contact angle measurements , cells in p = 20 cultures became less hydrophobic. Microelectrophoresis showed that isoelectric points shifted towards the acidic region upon serial passaging. Jn addition, the strains had become heterogeneous with respect to the pH dependence of their zeta potentials. According to FTIR and XPS, the surfaces of p = 20 cultures of both strains showed decreasing amounts of proteinaceous material and increasing amounts of polysaccharide-like substances as compared to p = 1 cultures. Heterogeneity of p = 20 strains was also reflected in structural features of the cell surface at the electron microscopic level. In p = 1 cultures of both strains, all cells had a stained layer: in contrast , in p = 20 cultures about half of the cells became devoid of this layer. The study clearly showed that surface characteristics of lactobacilli may change following serial passaging in liquid medium. Knowledge of these changes is of importance because these microorganisms are considered for use in biomedical applications like the restoration of a healthy vaginal microflora by cell seeding

New method to correct for the influence of organic contamination on intensity ratios in quantitative XPS

A new method is proposed to correct for attenuation effects by adventitious organic contamination in quantitative XPS, The corrected intensity ratio I-X(o)/I-Y(o) involving two different substrate peaks is determined as the slope of the plot of I-X/I-C1s as a function of I-Y/I-C1s for samples covered with organic overlayers of varying thickness. The thickness of deposited organic overlayers does not need to be perfectly uniform provided that it does not vary by more than +/-40%. The sample surface can either be flat or present a random roughness (e.g. powders), Shadowing effects accompanying overlayer non-uniformity are taken into account by a simple model involving effective thickness and fractional coverage, which is shown to enhance greatly the accuracy of computed intensity ratios. Constraints of the method and possible implementations were examined with an NaCl powder covered with adventitious contamination, polystyrene (PS) and polydimethylsiloxane (PDMS). The most straightforward implementation of the method would be to record repeatedly the peaks of interest while decreasing the adventitious contamination overlayer thickness by thermal desorption, The error on I-Na2s(o)/I-Na1s(o) is +10%, with the apparent overlayer thicknesses varying from 1.1 to 0.3 nm, The method is applied to check the reliability of the spectrometer transmission functions reported previously by Weng et al, Copyright (C) 1999 John Wiley & Sons, Ltd

Surface charging of insulating samples in X-ray photoelectron spectroscopy

Electrical charging of insulating samples during XPS is of direct concern for referencing the binding energy scale. Results are presented on charging of composite insulating samples that consist of an organic overlayer of polystyrene (PS) or polydimethylsiloxane (PDMS) deposited on NaCl particles. The samples were analysed using small-spot monochromatized radiation, the surface charge being stabilized with an electron flood gun. The charging shift of the NaCl substrate is influenced by three different factors: the total photoelectron flux, the energy of the electrons produced by the flood gun and the flux of electrons originating from the overlayer. The overlayer is acting as an additional electron source, which makes the substrate more negative and reduces inhomogeneities of the local potential affecting the peak full width at half-maximum. Comparison of substrate peak intensities with computed values showed that PS overlayers were less uniform compared to PDMS overlayers. The overlayer thickness and uniformity affect both the total photoelectron flux and the flux of electrons from the overlayer to the substrate. Overlayer charging, like substrate charging, is probably determined by the balance of electron fluxes in the phase considered. The kinetic energy of the photoelectron is determined by the electrical potential in the phase where photoemission occurs and not with respect to the sample surface. This was demonstrated by differential charging between the NaCl substrate and PS overlayer. (C) 1998 John Wiley & Sons, Ltd

INFLUENCE OF SOLUBLE POLYSACCHARIDE ON THE ADHERENCE OF PARTICULATE SOILS

peer reviewedThe removal of particulate soils from solid surfaces is the key process of cleaning many industrial devices, such as heat exchangers and spray dryers (food and pharmaceutical sector), and may be influenced by the presence of solutes, in particular of macromolecules. The present study deals with the influence of soluble polysaccharide on the adherence of particulate fouling of open surfaces and on subsequent cleaning. Model substrates differing by hydrophobicity (glass and polystyrene) were soiled with a suspension of quartz particles, taken as a model of hard hydrophilic soil. Dextran was chosen as a model of soluble polysaccharide. The substrates were soiled with or without previous conditioning with the polysaccharide solution (80mg/l). The quartz particles suspension was prepared in three ways: (i) suspension in a polysaccharide solution (80mg/l), (ii) same as (i) and subsequent washing three times, (iii) suspension in water. The substrates were soiled by spraying the suspension and dried for 30min before cleaning treatment with a water flow in a radial flow chamber. The aggregates observed after soiling differed considerably between glass and polystyrene, whether the substrate and/or the quartz particles were or were not conditioned with dextran. Conditioning polystyrene with dextran increased slightly the adherence of quartz particles, while the opposite was observed when conditioning glass with dextran, whatever the mode of quartz particles conditioning. The effect of conditioning quartz particles with dextran at the concentration used was not significant

Effet de la température sur l'intensité apparente des bandes de vibration de valence OH de solides inorganiques

Lorsqu'on enregistre les bandes de valence OH de nombreux minéraux maintenus à température élevée, tout en supprimant l'effet de l'émission, on observe une diminution de l'intensité d'absorption en fonction de la température.Rouxhet Paul G., Fripiat José Jean. Effet de la température sur l'intensité apparente des bandes de vibration de valence OH de solides inorganiques. In: Bulletin de la Classe des sciences, tome 57, 1971. pp. 101-124