The development of protein–polysaccharide conjugates via the Maillard reaction represents a promising strategy to enhance the techno-functional properties of food proteins while simultaneously incorporating bioactive or prebiotic carbohydrates. In this study, whey protein isolate (WPI) was conjugated with two distinct prebiotic carbohydrates—Inulin and galactooligosaccharides (GOS)—and the structural, functional, and interfacial characteristics of the resulting conjugates were compared. Reaction conditions were optimized to promote controlled conjugation while minimizing excessive browning. The degree of conjugation, structural modifications, and changes in molecular properties were characterized using SDS-PAGE, FTIR spectroscopy, fluorescence analysis, and browning index measurements.

Both WPI–Inulin and WPI–GOS conjugates exhibited improved solubility and thermal stability relative to native WPI, although the magnitude of these improvements differed depending on the carbohydrate type. WPI–GOS conjugates showed a higher degree of glycation, likely due to the smaller molecular size and higher reducing sugar activity of GOS, leading to more extensive protein modification. In contrast, WPI–Inulin conjugates, characterized by lower reducing-end activity and higher molecular weight, generated less pronounced structural alterations but produced thicker conjugate layers at interfaces.

Interfacial tension measurements and droplet stabilization tests revealed key functional differences: WPI–GOS conjugates displayed faster adsorption kinetics and improved emulsifying capacity, attributed to their enhanced solubility and increased hydrophilicity following glycation. WPI–Inulin conjugates, however, formed more viscoelastic and robust interfacial layers, resulting in superior resistance to coalescence and improved long-term emulsion stability. These findings demonstrate that carbohydrate size, structure, and reducing-end activity critically influence the interfacial behavior of protein–carbohydrate conjugates.

Beyond their functional performance, both conjugates provide additional prebiotic benefits. GOS conjugates deliver short-chain oligosaccharides known for selective stimulation of bifidobacteria, while Inulin conjugates incorporate longer fructans capable of modulating gut microbiota composition and enhancing fermentation profiles in the colon. The successful formation of WPI–Inulin and WPI–GOS conjugates therefore offers dual advantages: enhanced protein functionality and the integration of prebiotic components into delivery structures.

Overall, this comparative study highlights how the choice of carbohydrate significantly affects the molecular, interfacial, and techno-functional properties of WPI-based conjugates. WPI–GOS conjugates excel in improving protein solubility and rapid interfacial adsorption, whereas WPI–Inulin conjugates provide greater interfacial strength and emulsion stability. These insights support the development of next-generation prebiotic–protein conjugates for functional food emulsions, nutraceutical delivery systems, and gut-health-promoting formulations.

Conference theme: physical properties of food hydrocolloids for enhanced product development