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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 (A_294nm/A_420nm), 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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This study was aimed to investigate the effect of Maillard reaction browning intensity (BI) on the interfacial properties of emulsion systems stabilized by soy protein isolate. The covalent bonding between soy protein isolate and gellan gum was confirmed by the BI and then the resulting protein-polysaccharide conjugates were classified into three low, medium, and high BI clusters using Hierarchical Agglomerative Clustering (HAC) method. Next, the emulsification properties (emulsifying capacity, emulsion stability, and the percentage of adsorbed protein), thermal stability, and rheological behavior of emulsion systems stabilized by the above clusters were evaluated. The emulsifying capacity and emulsion stability were increased more efficiently by the high BI soy protein isolate-gellan conjugate, showing its faster migration and absorption rate, and consequently higher percentage of absorbed protein to the interface, and also form a thicker, cohesive, and viscoelastic interfacial layer along with more steric repulsion at its oil/water interface. In addition, the apparent viscosity of emulsions in the presence of high BI conjugate was significantly higher than the systems stabilized by other conjugates (p<0.05). However, due to the more unmasked hydrophobic patches of the high BI conjugated protein, the thermal stability of its emulsion was lower compared to other counterparts. Therefore, the Maillard reaction under mild and controlled conditions along with minimal final compounds formation can improve the interfacial properties of soy protein to improve its application in the food industry.