Obesity significantly reduces quality of life and imposes a substantial socioeconomic burden. Increasing evidence links excessive fat intake to elevated risks of cardiovascular disease, certain cancers, and multiple chronic diseases. Therefore, the development of an effective dietary supplement that can mitigate intestinal fat absorption is of considerable interest. This study provides systematic evidence for a pH-engineered lecithin–soy protein microcage embedded within a κ-carrageenan hydrogel matrix for targeted intestinal fat trapping.

To fabricate the microcage, lecithin (2%) and soy protein isolate (2%) were dispersed in ethanol and mixed at 60 °C for 4 h under 500 rpm stirring. A pH-shifting treatment (pH 3, 7, and 10) was then applied to modulate the soy protein–lecithin phospholipid interactions and promote a functional self-assembly. The resulting dispersion was evaporated to dryness to remove ethanol and reconstituted in Milli-Q water. This concentrated suspension was introduced dropwise into a 2% κ-carrageenan solution (60 °C, 500 rpm, 4 h) to form a composite hydrogel, followed by cooling and overnight crosslinking in 0.3% KCl.

Comprehensive characterisation was conducted to evaluate the microcage formation, embedding efficiency, and digestive behaviour. FTIR, SEM, intermolecular force analysis, dynamic oscillation, and contact-angle measurements collectively demonstrated that the lecithin–soy protein microcages were stabilised predominantly by hydrophobic interactions. Particle-size analysis and CLSM confirmed successful incorporation of ~1 µm microcages into the κ-carrageenan network. pH shifting significantly influenced both zeta potential and hydrophobicity: microcages were positively charged at pH 3, while negative zeta potentials were observed at pH 7 and 10. Hydrophobicity increased markedly at pH 10, attributed to the enhanced exposure of hydrophobic domains caused by protein unfolding under alkaline conditions. Interactions with κ-carrageenan were likewise pH-dependent—positively charged microcages at pH 3 bound electrostatically to the anionic polysaccharide, whereas neutral or negatively charged microcages at higher pH were primarily incorporated through physical entrapment within the gel network.

In vitro oil-absorption capacity, evaluated using GC-FID and CLSM, revealed that the κ-carrageenan–embedded microcages absorbed at least 50% of added rice bran oil, with strong retention of long-chain fatty acids (e.g. palmitic acid; C16 and linoleic acid; C18:2), likely due to their pronounced hydrophobic nature. Among all treatments, the pH 10 microcage system exhibited the highest absorption capacity, consistent with its increased hydrophobicity. In vitrodigestion studies also demonstrated that the composite hydrogel maintained structural integrity throughout gastrointestinal transit without being fragmented into fine particles, indicating its potential for safe passage and excretion following lipid sequestration.

Overall, this work presents a practical and scalable strategy for constructing protein–phospholipid microcages embedded within a carrageenan matrix for targeted intestinal oil entrapment. The findings provide new insights into pH-induced hydrophobic modulation in microcage assembly and subsequent function, offering a useful approach for developing the next-generation of fat-reducing dietary supplements.