Gelatin-polyelectrolyte polysaccharide complexes for encapsulation of natural pigments: formation mechanisms and functionality

Gelatin, a popular protein, is limited by its uneven structure and mechanical and thermal defects, whereas polyelectrolyte polysaccharides can improve it by electrostatic interactions and promote encapsulation of naturally functional pigments in the resulting emulsions for functional applicability. The electrostatic bases of gelatin, including the isoelectric point effect, screening effect, and Hofmeister effect, are discussed. Electrostatic regulation on gelatin-polyelectrolyte polysaccharides owing to amino groups, carboxy groups, sulfate groups, phosphate groups, octenyl succinic anhydride, pyruvate groups, etc., is summarized, which induces variable emulsifying abilities. After the encapsulation of naturally functional pigments, the coloring mechanisms of gelatin-polyelectrolyte polysaccharide-based emulsions are analyzed in terms of pigment types and color quantification models (e.g., Kubelka-Munk). The functionalities of gelatin-polyelectrolyte polysaccharide-based emulsion systems containing naturally functional pigments, including nutrition, bioactivity, smartness, and innovation, are reviewed. This work proposes future development directions (structure-coloring mechanism-function relationships) and possible prospects for the efficient molecular design of gelatin-polyelectrolyte polysaccharide-natural pigments based on functionally colored emulsions for future food applications.