Biomedical subjects

Aude Vernhet

Publications and source records attributed to Aude Vernhet.

3 recordsLinked to original sources

PubMed2006

Polar interactions in flavan-3-ol adsorption on solid surfaces.

The adsorption of flavan-3-ol monomers and grape seed procyanidin fractions of different mean degrees of polymerization was studied on three surfaces by means of adsorption isotherms. Reversibility upon dilution was also investigated. These surfaces were three polymeric microfiltration membranes, presenting close Lifshitz-van der Waals components of their surface tension but differing in their surface polar properties. The electron-donor character of the surface was of primary importance for the adsorption of nongalloylated monomers. Increasing the number of phenolic rings above two (galloylated monomers and procyanidins) sharply enhanced flavan-3-ol affinity for surfaces whatever their polarity. However, maximum adsorbed amounts were always much higher on the most polar material. The general trend was a partial reversibility with monomers, whereas an irreversible process was evidenced from the lowest molecular weight tannin fractions. This indicated the formation of multiple bonds with surfaces, in accordance with the high affinity type isotherms. The whole results indicated very different mechanisms in the buildup of the adsorbed layers when the surface electron-donor character varied.

Adsorption↗

PubMed2006

Shear-flow induced detachment of Saccharomyces cerevisiae from stainless steel: influence of yeast and solid surface properties.

The present study focused on the shear-induced detachment of Saccharomyces cerevisiae in adhesive contact with a 316L stainless steel surface using a shear stress flow chamber, with a view to determining the respective influence of the yeast surface properties and the support characteristics. The effect of cultivation of S. cerevisiae yeast cells on their subsequent detachment from the solid surface was particularly investigated. In order to elucidate the role of stainless steel, non-metallic supports were used as control, covering a broad range of surface properties such as surface free energy and roughness: polypropylene (hydrophobic), polystyrene (mildly hydrophobic, similar to stainless steel) and glass (hydrophilic). All materials were very smooth with respect to the size of yeast. First, experiments were carried out on two types of yeast cells, just rehydrated in saline solution, a biological model widely used in the literature. The influence of the ionic strength (1.5 and 150 mM NaCl) on glass and stainless steel was evaluated. Unlike on glass, no clear evidence was found for electrostatic repulsion with stainless steel since high adhesion was observed whatever the ionic strength. A lack of correlation in adhesion results was also obtained when considering the surface physico-chemical characteristics of type I (hydrophilic) and type II (hydrophobic) rehydrated cells and those of both polymers. It was postulated that unavoidable "sticky" compounds were present on the cell wall, which could not be completely removed during the successive washings of the rehydrated cell suspension before use. This could dramatically alter the yeast surface properties and modify the adhesion strength, thus clearly demonstrating the necessity to work with yeast coming from fresh cultures. Biologically active yeast cells were then used. Once cultured, type I- and type II-yeast cells were shown to exhibit the same hydrophilic properties. Regardless of the material used, for the same ionic strength (150 mM NaCl), yeast adhesion was drastically reduced compared to rehydrated yeast cells. Among all the materials tested, the specificity of 316L stainless steel was clearly established. Indeed, for glass and polymers, cell adhesion was substratum-dependent and driven by the balance between the Lifshitz-van der Waals and Lewis acid/base interactions. Despite nearly identical surface free energies for polystyrene and stainless steel, the metallic surface promoted a totally distinct behaviour which was characterized by a strong - although highly variable - yeast adhesion.

Cell Adhesion↗

PubMed2005

Formation of micella containing solubilized sterols during rehydration of active dry yeasts improves their fermenting capacity.

During their rehydration in aqueous media, active dry yeasts (ADY) may be supplemented with inactive yeasts, yeast derivatives, or other optional complementary nutrients to improve their fermentation capacity. We found that yeast sterols solubilized in situ during ADY rehydration were particularly efficient for stimulating the fermenting capacity of ADY. Spontaneous solubilization of sterols during rehydration occurred by the formation of micelles by membrane phospholipids and specific cell wall polysaccharides and sterols, both compounds being provided by inactive dry yeasts (IDY). These micelles contained a specific distribution of the initial sterols from the inactive yeasts. Above a concentration of 100 mg L(-1) in the rehydration medium, these micelles acted as emulsifiers. Their critical micellar concentration (cmc) was found to be about 4 g L(-1). During rehydration, purified micelles, at a concentration near the cmc, were able to interact quickly with yeast cell membranes by modifying the yeast plasma membrane order [monitored by steady-state fluorescence anisotropy of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene-p-toluenesulfonate (TMA-DPH) probe] and by increasing the sterol contents of ADY. Such an enrichment of ADY by very low concentrations of solubilized sterols was very efficient for the completion of fermentations. This is useful when musts are limited in available phytosterols or when micro-oxygenation is not desirable during fermentation.

Cell Wall↗