Search

To enhance physico-chemical properties of alginate liquid-core capsules, shellac was incorporated into the membrane (composite capsules) or as an additional external layer (coated capsules). The influence of pH, coating time, shellac concentration and preparation mechanism (acid or calcium precipitation) were investigated. Results showed that shellac significantly influenced the capsules properties. The feasibility of shellac incorporation was closely related to the preparation conditions as confirmed by Infrared spectroscopy. Optical, fluorescence and scanning electron microscopy, highlighted different capsules and membranes architectures. In contrast to simple and composite capsules, coated capsules showed a pH-dependent release of the entrapped vitamin especially after shellac crosslinking with calcium. Heating of coated capsules above the glass transition temperature investigated by Differential Scanning Calorimetry, led to irreversible structural change due to thermoplastic behavior of shellac and enhanced riboflavin retention under acidic conditions. This global approach is useful to control release mechanism of low molecular weight molecules from macro and micro-capsules.

International audience; Hypothesis: Alginate capsules have several applications. Their functionality depends considerably on their permeability, chemical and mechanical stability. Consequently, the creation of composite system by addition of further components is expected to control mechanical and release properties of alginate capsules. Experiments: Alginate and alginate-sodium caseinate composite liquid-core capsules were prepared by a simple extrusion. The influence of the preparation pH and sodium caseinate concentration on capsules physico-chemical properties was investigated. Findings: Results showed that sodium caseinate influenced significantly capsules properties. As regards to the membrane mechanical stability, composite capsules prepared at pH below the isoelectric point of sodium caseinate exhibited the highest surface Young's modulus, increasing with protein content, explained by potential electrostatic interactions between sodium caseinate amino-groups and alginate carboxylic group. The kinetic of cochineal red A release changed significantly for composite capsules and showed a pH-responsive release. Findings: Sodium caseinate-dye mixture studied by absorbance and fluorescence spectroscopy confirmed complex formation at pH 2 by electrostatic interactions between sodium caseinate tryptophan residues and cochineal red sulfonate-groups. Consequently, the release mechanism was explained by membrane adsorption process. Findings: This global approach is useful to control release mechanism from macro and micro-capsules by incorporating guest molecules which can interact with the entrapped molecule under specific conditions.

Hypothesis To enhance physicochemical properties of alginate aqueous-core capsules, conventional strategies were focused in literature on designing composite and coated capsules. In the present study, own effect of liquid-core composition on mechanical and release properties was investigated. Experiments Capsules were prepared by dripping a CaCl2 solution into an alginate gelling solution. Viscosity of CaCl2 solution was adjusted by adding cationic, anionic and non-ionic naturally derived polymers, respectively chitosan, xanthan gum and guar gum. In parallel, uniform alginate hydrogels were prepared by different methods (pouring, in situ forming and mixing). Mechanical stability of capsules and plane hydrogels were respectively evaluated by compression experiments and small amplitude oscillatory shear rheology and then correlated. Capsules permeability was evaluated by monitoring diffusion of encapsulated cochineal dye, riboflavin and BSA. The core–shell interactions were investigated by ATR-FTIR. Findings Results showed that inner polymer had an impact on membrane stability and could act as an internal coating or provide mechanical reinforcement. Mechanical properties of alginate capsules were in a good agreement with rheological behavior of plane hydrogels. Release behavior of the entrapped molecules changed considerably. This study demonstrated the importance of aqueous-core composition, and gave new insights for possible adjusting of microcapsules physicochemical properties by modulating core–shell interactions.