Physico-chemical properties of alginate/shellac aqueous-core capsules: Influence of membrane architecture on riboflavin release

•Shellac was combined with alginate in the membrane or at the surface of capsules.•Feasibility of shellac incorporation was closely related to experimental conditions.•Shellac was incorporated by acid precipitation or calcium reticulation.•Microscopic study highlighted different capsule and membrane architectures.•Coated capsules by calcium reticulation showed high riboflavin retention. 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.