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.