Changes in physicochemical properties and gelation behaviour of caseinomacropeptide isolate by treatment with transglutaminase

The gelation behaviour of caseinomacropeptide isolate (CMPI) treated with transglutaminase at levels of 1 and 25 U g−1 protein was investigated at different pH and temperatures. Cross-linking of CMPI protein fractions by transglutaminase was confirmed using tricine-sodium dodecylsulphate-polyacrylamide gel electrophoresis. Cross-linking reduced the isoelectric point and hydrophobicity of CMPI. The gelation temperature of CMPI at pH 3 was reduced from 54 to 42 °C; a gel point (G'>1 Pa) was not observed at pH 4.5 after enzyme treatment during temperature sweep measurements. Cross-linked CMPI formed a gel with lower stiffness and fracture stress at 90 °C at pH 3.0 or 4.5 compared with gels of untreated CMPI. However, stiffness and fracture stress of CMPI gels formed at 70 °C at pH 3.0 increased by three- and four-fold, respectively, by cross-linking with 25 U g−1 protein of enzyme. Transglutaminase affected gelation of CMPI by cross-linking of both CMP and residual whey proteins.