Effect of the degree of blockiness on the glycosylation and emulsification of citrus pectin-whey protein isolate conjugates.

BACKGROUND: Maillard reaction-derived pectin-protein conjugates are common functional food emulsifiers. As a key structural parameter of citrus pectin (CP), the blockiness degree (DB) independently regulates the Maillard reaction between CP and whey protein isolate (WPI) and the emulsifying properties of their conjugates, which remains poorly understood. This study aimed to clarify such regulatory mechanisms to support the targeted development of high-performance pectin-protein emulsifiers. METHOD: CP samples with similar methoxylation degrees (34.2-36.7%) and varied DB (27.4-88.3%) were prepared via sequential enzymatic de-esterification with plant and fungal pectin methylesterases. Dry heating was subsequently applied to trigger Maillard conjugation between modified CP and WPI, and the emulsion test was performed. RESULT: DB significantly accelerated the glycation reaction, raising the glycation degree of CP-WPI conjugates from 48.2% to 66.7%. This improvement stemmed from increased local charge density and better accessibility of pectin neutral sugar side chains to WPI during dehydration. At equivalent glycation levels, high-DB conjugates exhibited lower surface hydrophobicity, thicker hydrated interfacial layers and stronger steric-electrostatic stabilization, with only slightly impaired interfacial adsorption. All conjugates showed better interfacial activity and emulsifying performance than native WPI. CONCLUSION: CP DB is a decisive factor governing the CP-WPI Maillard reaction efficiency and conjugate emulsifying functionality. Modulating pectin DB is a reliable strategy to fabricate pectin-protein emulsifiers with tunable functions, providing practical guidance for the preparation of high-efficiency food emulsifiers.