Modulating limonin release via pectin fine structure in Ca²⁺-citrus pectin emulsion gels

Despite the well-established role of calcium in pectin gelation, the regulatory mechanisms by which Ca²⁺ concentration governs the microstructure and functionality of emulsion gels derived from citrus pectin remain poorly understood. This study bridges this knowledge gap by employing citrus pectin with distinct fine structures to fabricate emulsion gel system via Ca²⁺-mediated cross-linking, systematically elucidating the influence of Ca²⁺ on gel microstructure, rheology, and stability. The results demonstrated that low-methoxyl pectin (LMP) formed a dense gel network through Ca²⁺ cross-linking. In contrast, the structure of high-methoxyl pectin (HMP) emulsion gels was stabilized predominantly by hydrophobic interactions. An increased ratio of rhamnogalacturonan I (RGI) side chains enhanced hydrogen bonding interactions, though excessive Ca²⁺ (10 mM) induced localized over-crosslinking in LM.HRGI, increasing droplet size and reducing homogeneity. In vitro digestion experiments revealed that LM.HRGI-based emulsion gels facilitated rapid limonin release in the colon (release rate constant k = 0.54 min^-1), whereas HMP-based gels showed sustained intestinal release (k = 0.17 min^-1). The encapsulation efficiency of limonin reached 85.24 % in optimally formulated LM.LRGI-based emulsion gels (5 mM Ca²⁺). The study established a quantitative structure-gel property-delivery behavior relationship model, demonstrating that the multivariate fine structure of pectin dictates the digestion fate of loaded bioactives, providing a foundational principle for the engineering of functional foods and precise design of nutraceutical delivery systems.