Casein and pectin: Structures, interactions, and applications

Proteins and polysaccharides are the most abundant biomaterials and often present together in food and biological systems. The exploitation of protein-polysaccharide interactions offers opportunities for the design of new ingredients and biopolymeric complexes with applications in different fields. Casein and pectin are two examples of most extensively studied proteins and polysaccharides in recent years, and can be used to create different types of colloidal systems with unique properties, including nanoparticles, microparticles, emulsions, hydrogels and films. This review sets out our current understanding of the nature of casein and pectin, and their interactions at the molecular level in different contexts, i.e. acidified milk drinks, oil-in-water emulsions, particulate and other colloidal systems. The affecting factors, including pH, ionic strength, concentrations of two biopolymers, processing factors, and others are considered. Furthermore, current and potential food and pharmaceutical applications of some selected colloidal systems are also discussed with illustrative examples. It has been revealed that the interactions between casein and pectin in their mixed system and a more complex system where a hydrophobic phase is present, could happen as co-solubilization, thermodynamic incompatibility, complexation, flocculation or segregation. The understanding of casein-pectin interaction mechanisms offers the possibility to design tailor-made colloidal systems, which have great applications in enhancing stability of acidified milk drinks and emulsions, encapsulation and protection as well as controlled release of bioactive compounds, developing edible packaging films and fat replacement for various food products.