Impact of acidic and basic pH on the interfacial shear rheology and foaming properties of transglutaminase cross-linked casein micelle: Structure-function relationship

This work investigated the pH effect (pH 3.5 to 9.0) on the interfacial behavior of native and transglutaminase cross-linked (TGase) caseins films at air-water interface using a rotational rheometer equipped with a BiCone geometry. Both caseins formed a viscous-like interfacial adsorbed layer within the range of frequency from 0.1 to 10 rad/s, with a maxima viscoelastic layer at alkaline pH (8.0 and 9.0). TGase caseins exhibited the highest interfacial shear surface moduli values, and the difference between them was pronouncedly, under acid pH conditions (3.5 to 5.5). The conformational studies revealed the pH and transglutaminase cross-linking effect on the protein structure. The foaming properties suggested a weakening and strengthening of foaming capacity and stability, respectively, by TGase in alkaline pH conditions. The combination of pH-shifting and transglutaminase treatment, especially, under alkaline pH conditions might be applied to improve the casein ability to stabilize the foams in several food applications. • Viscoelastic behavior of cross-linked casein significantly depends on pH value. • Formation of strengthened film for pH 8.0 and 9.0. • Maximum foam capacity and stability for pH 8.0 and 9.0. • Conformation modifications were reflected in viscoelastic and foaming properties. • Cross-linking in alkaline pH could be used to enhance protein functionalities.