This study was aimed to investigate the effect of Maillard reaction polymerization degree (PD) on functional properties of whey protein isolate. The whey protein isolate-gellan gum conjugate was synthesized by the Maillard reaction and the intermediate-to-final products absorption ratio (A294nm/A420nm), as the index of Maillard reaction PD, was evaluated. The whey protein isolate-gellan gum conjugates were then classified into three low, medium, and high PD using K-means clustering method, and their interfacial activity (interfacial tension reduction ability, emulsifying activity, and emulsion stability) and surface activity (foaming capacity and foam stability) were investigated. Interfacial tension at oil/water interface was reduced more efficiently by the medium PD whey protein isolate-gellan conjugate, indicating its higher adsorption rate to the interface (higher emulsifying activity), ability to form a viscoelastic thick layer at interface, and consequently increase the emulsion stability through steric repulsion. Although, foaming capacity was not significantly influenced by the PD (p>0.05), the foam stability in the presence of medium PD conjugate was significantly higher than the foams stabilized by other conjugates (p<0.05). Therefore, a medium PD is needed to improve the functional properties of whey protein and increase its industrial applications.

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