Influence of pea protein-κ-carrageenan composite microgel particle interfacial structure on lipid digestibility in O/W Pickering emulsions

The impact of interfacial structure on lipid digestion of emulsions remains controversial, presenting a key limitation in developing technologies for precise regulation of nutritional characteristics through rational food structure design. This study employed pea protein isolate (PPI) microgel particle (PPM) and PPI-κ-carrageenan (κ-CG) composite microgel particle (PPCM) as a model system. The mixing ratio of these macromolecules was adjusted, which changed the interaction of protein and polysaccharide molecules, as well as the interfacial structure of PPCM. Subsequent analysis of structural changes and emulsion digestion in an in vitro simulated digestion model elucidated the regulatory mechanism of interfacial structure on lipid digestion of Pickering emulsions (PPM-E and PPCM-E). The results demonstrated that free sulfhydryl and hydrophobic groups embedded in PPI became exposed during the heat-shearing process of microgel preparation, facilitating disulfide bond formation. The κ-CG gel associated with PPI gel through non-covalent bonds, effectively shielding the exposed hydrophobic groups of PPI. Based on the thickness of the interface, the amount of adsorbed protein, and the protein concentration at the interface, and the surface dilatational modulus, it was found that the deformability of microgel particles at the interface varies. This variation leads to differences in the interfacial structure: PPM formed thick but sparsely distributed interfacial layers due to its limited interfacial deformability; PPCM1 and PPCM2 formed thinner and denser interfacial layers with exposed κ-CG gels on the surface owing to because of their greater deformability compared to PPM; PPCM3, PPCM4, and PPCM5 exhibited the thinnest and densest interfacial layers among the microgel particles, with the exposed κ-CG interconnected to form a polysaccharide network surrounding the oil droplets. Compared with PPM-E, the κ-CG outside the interfacial layer of PPCM1-E and PPCM2-E promoted the expansion of the interfacial microgel in the simulated intestinal fluid and enhanced the hydrolysis by trypsin and lipase, resulting in higher free fatty acid (FFA) release than PPM. In contrast, the κ-CG network outside the interfacial layer of PPCM3-E, PPCM4-E, and PPCM5-E impeded the trypsin and lipase activity, thereby inhibiting the lipid digestion and resulting in lower FFA release than PPM.