The instability of pectin-based emulsions in the upper digestive tract investigated based on the molecular structure and interfacial properties of pectin

Pectin is a widely used natural emulsifier that is thought to stabilize emulsions in the upper gastrointestinal tract (GIT). However, changes in the structural characteristics and interfacial properties of pectin during its digestive treatment in the upper GIT and the effects on the stability of pectin-based emulsions are still unclear. This study showed that the stability of pectin-based emulsions steadily decreased in the upper GIT. Reductions in the molecular weight of pectin (from 2.74× 10⁵ to 1.61× 10⁵ g/mol) occurred mainly in the stomach, whereas the degree of esterification (from 61.2 % to 42.1 %) decreased throughout the digestive treatment. The change in the structure of pectin reduced its hydrophobicity in the upper GIT, and led to form a cross-linked network with Ca²⁺ in small intestine rather than adsorbing to the oil-water interface. The behavior was reflected in the increased interfacial tension and the decreases in the interfacial modulus and thickness of pectin. Our insights into the structural characteristics and interfacial properties of pectin and thus into the mechanism of pectin instability in the upper GIT will contribute to the development of more efficient encapsulation methods and improved targeted delivery for active substances or probiotics using pectin-based emulsions.