Influence of chemically modified alginate esters on the preparation of microparticles by transacylation with protein in W/O emulsions.

Microencapsulation using the transacylation reaction in a W/O emulsion is based on the creation of amide bonds between the protein's amine functions and the ester groups of a polysaccharide in the aqueous phase after alkalization. Commercial propylene glycol alginate (PGA) has been the only modified polysaccharide involved in the process up to now. In the present work, we describe the effect of substituting the commercial PGA by other chemically modified alginates in the formation of microparticles. Alkyl and hydroxyalkyl alginate esters, were synthesized and tested in the encapsulation process with human serum albumin (HSA). It was found that the hydroxyalkyl alginates were suitable polysaccharide substitutes for PGA in the transacylation reaction, whereas the alkyl alginates did not lead to microparticle formation in the same process. Hydroxyalkyl alginates with high esterification degree (DE) (>50) led to microparticles when involved in the preparation procedure. However with lower DE (<30), no microparticles could be obtained from 2% ester solution concentrations. This difference in reactivity was explained by the formation of hydrophobic microdomains with the alkyl esters that hindered the transacylation reaction, as opposed to hydroxyalkyl esters that bore hydrophilic ester groups.

Serum Albumin-Alginate Microparticles Prepared by Transacylation: Relationship between Physicochemical, Structural and Functional Properties.

Our laboratory develops a method of microencapsulation using a transacylation reaction in a water-in-oil (W/O) emulsion. The method is based on the creation of amide bonds between free amine functions of a protein (human serum albumin (HSA)) and ester groups of propylene glycol alginate (PGA) in the inner aqueous phase after alkalization. The aim of this work is to study the influence of physicochemical properties of HSA-PGA mixtures on microparticle characteristics. Microparticles were prepared varying the concentrations of PGA and HSA, then characterized (inner structure, size, swelling rate, release kinetics). PGA and each polymer mixture used in the microencapsulation procedure were examined in order to elucidate the mechanism of microstructure formation. It was found that the morphology and functional properties of HSA-alginate microparticles were related to the two polymer concentrations in the aqueous solution. Actually, the polymer concentration variations led to physicochemical changes, which affected the microparticle structure and functional properties.

Gradient elution method in centrifugal partition chromatography for the separation of a complex sophorolipid mixture obtained from Candida bombicola yeasts.

Sophorolipids represent an important class of natural surfactants with a variety of environmental, cosmetic, and pharmaceutical applications. Despite their promising physicochemical and biological properties, the use of sophorolipids is hampered by the lack of information regarding their individual structure-activity relationships. The major difficulty in isolating pure sophorolipids arises from the high complexity of crude fermentation media composition and from their strong structural similarities. In this work, a centrifugal partition chromatography method was developed in an original gradient elution mode for the separation of sophorolipids produced by the yeast Candida bombicola. Experiments were realized by using three sets of solvent systems composed of n-heptane, ethyl acetate, n-butanol, methanol, and water in different proportions. The separation was performed at 5 mL/min in the ascending mode by increasing progressively the polarity of the organic mobile phase. In these conditions, more than 80% of the sophorolipids present in the initial crude fermentation extract were eluted successively from the most hydrophobic lactone forms to the most hydrophilic acid forms. The structures of the isolated sophorolipids were further elucidated by HPLC and NMR analyses.