Hary Razafindralambo

Purification Of Antifungal Lipopeptides By Reversed-Phase High-Performance Liquid-Chromatography

A rapid procedure for the purification of antifungal lipopeptides from Bacillus subtilis, a potential agent for biocontrol of plant diseases, was tested. It consists of a solid-phase extraction on C18 gel followed by reversed-phase chromatography using a biocompatible PepRPC HR 5/5 column with a pharmacia fast protein liquid chromatographic system. This is a very effective method for isolating and fractionating iturin A and surfactin, two lipopeptides of different nature, co-produced by Bacillus subtilis strain S499. The presence of homologous lipopeptides was easily detected.

Foaming properties of a natural cyclic lipoheptapeptide belonging to a special class of amphiphilic molecules

Abstract The foaming properties of surfactin, a natural cyclic lipoheptapeptide from Bacillus subtilis, were investigated in comparison and in association with those of bovine serum albumin (BSA). An apparatus combining bubbling, optical and conductimetric methods was used to study continuously foam formation and stability in terms of the quantity and density offoam. The increase in surfactin concentration from 0.05 to 0.2 mg/ml had little effect on its foaming capacity, measured by the bubbling time to produce the required foam volume, but improved the foam maximum density significantly. Surfactin produced foam with higher maximum density and stability, and forms more regular and smaller bubbles than BS A. In addition, a synergistic effect was observed on the stability of liquid in foam prepared with a mixture of 50:50 surfactin/BS A. The liquid half-life of BSA foam was enhanced up to 40% when surfactin was added to the solution.

Monolayer Properties of Uronic Acid Bicatenary Derivatives at the Air-Water Interface: Effect of Hydroxyl Group Stereochemistry Evidenced by Experimental and Computational Approaches

By screening uronic acid-based surfactant interfacial properties, the effect of the hydroxyl group stereochemistry (OH-4) on the conformation of bicatenary (disubstituted) derivatives at the air-water interface has been evidenced by experimental and computational approaches. Physical and optical properties of a monolayer characterized by Langmuir film balance, Brewster angle microscopy, and ellipsometry at 20 °C reveal that the derivative of glucuronate (C(14/14)-GlcA) forms a more expanded monolayer, and shows a transition state under compression, in the opposite to that of galacturonate (C(14/14)-GalA). Both films are very mechanically resistant (compression modulus > 300 mN m(-1)) and stable (collapse pressure exceeding 60 mN m(-1)), while that of C(14/14)-GalA exhibits a very high compression modulus up to 600 mN m(-1) like films in the solid state. Computational approaches provide single and assembly molecular models that corroborate the molecule expansion degree and interactions data from experimental results. Differences in the molecular conformation and film behaviours of uronic acid bicatenary derivatives at the air-water interface are attributed to the intra-H-bonding formation, which is more favourable with an OH-4 in the axial (C(14/14)-GalA) than in the equatorial position (C(14/14)-GlcA).

Foamability and Foam Stability of Male and Female Date Palm Sap (Phoenix dactylifera L.) During the Collection Period

This work aimed to study the influence of date palm sex on the surface properties of date palm sap (DPS) (Phoenix dactylifera L.) during the collection period. The behavior at the interface and foaming properties were evaluated via equilibrium surface tension (drop volume) and bubbling method, respectively. Unlike male sap, the female sap was unable to produce foam due to its low rate of adsorption, low average hydrophobicity values, and low bulk viscosity values throughout the collection period. For male sap, there are significant differences (pu2009<u20090.05) on foaming properties throughout the collection period. In fact, the last 3xa0weeks of sap collection were characterized by a decrease pace of surface tension which explains the enhancement of both foam capacity and stability. The last week of collection period present the best foam power (0.9). To explain these differences, the interactions of several factors and their affects on foaming properties were examined. Results showed a positive correlation between foam capacity and average hydrophobicity values. In the other hand, foam stability exhibits a positive correlation with the increase of protein concentration and bulk viscosity.

Physico-chemical approach for characterizing probiotics at the solid and dispersed states

A physico-chemical approach was used for characterizing and generating fingerprints of single (L. bulgaricus and S. thermophilus) and multiple (Vivomixx) probiotic species. Such a methodology included thermal, colloidal, and surface analyses of powder (solid-in-gaseous phase) and dispersed (solid-in-aqueous phase) samples. Decomposition and transition phases analyzed by thermogravimetry and differential scanning calorimetry provide specific qualitative and quantitative data that serve as a probiotic fingerprint, and therefore a product quality control for each sample. Investigation of colloidal and surface properties of dispersed samples by light scattering and contact angle measurements informs on the probiotic size average, electrokinetic charge, and surface hydrophobicity. Besides their relevance in identity control, the physico-chemical data are also useful in probiotic performance prediction, since they govern the most crucial microbial functionalities such as thermostability, aggregation, and adhesion.