Maillard conjugates of casein and isomaltooligosaccharides enhance solubility and emulsifying properties for clean-label dairy applications

To enhance the performance of CN as a natural emulsifier in complex food systems, this study prepared CN-isomaltooligosaccharide (IMO) conjugates via Maillard reaction under wet-heat conditions, systematically investigating their structural and functional changes. With increasing CN-IMO ratio, the grafting degree first increased and then decreased, reaching a maximum of 36.39% in the CI53 sample (CN:IMO = 5.3). Sodium dodecyl sulfate-PAGE, Fourier-transform infrared spectroscopy, UV-visible spectroscopy, and fluorescence spectroscopy indicated covalent bonding between CN and IMO, accompanied by significant protein conformational rearrangement. The Maillard reaction reduced the micelle size to 207.57 nm and made the ζ potential more negative (-30.38 mV), thereby enhancing colloidal stability. Compared with CN, CI53 exhibited improvements of 21.02% in emulsifying stability, 10.24% in solubility, and 139.06% in oil-holding capacity. Reductions in contact angle and surface hydrophobicity implied improved surface hydrophilicity due to hydroxyl group introduction. This study provides theoretical and technical support for developing clean-label casein-oligosaccharide natural emulsifiers.