Effect of transglutaminase-induced cross-linking of sodium caseinate on the properties of equilibrated interfaces and foams

The effect of transglutaminase (TG)-induced cross-linking on interfacial rheology and foam stability was investigated in sodium caseinate systems. Higher dilatational surface moduli values were found, when cross-linking was performed at an equilibrated interface. However, cross-linking prior to adsorption was not found to affect the moduli values, but increased the equilibrium surface tension value. Foaming ability of cross-linked sodium caseinate was little reduced, when short reaction times with the enzyme were used, but a considerable loss in foaming ability was observed with extensive cross-linking prior to foaming. Stability against drainage was increased with increasing reaction time. With 15 min reaction at 40 °C with 200 nkat/g TG, no liquid drainage was observed 2 h after foaming from 10% sodium caseinate foam. Much smaller bubbles were found in enzyme-treated foams as compared with the reference sodium caseinate foam at 30 min, 2 h and 24 h after foaming. TG-treatment retarded but did not inhibit bubble coarsening in foams. Most likely, the effects in stability were due to increase in continuous phase viscosity.