The effect of transglutaminase treatment on the physico-chemical properties of skim milk with added ethylenediaminetetraacetic acid

The influence of transglutaminase (TG) treatment on the changes in the physico-chemical properties of reconstituted skim milk (10 wt%) with different amounts of added ethylenediaminetetraacetic acid (EDTA) (0–50 mM) was studied. The partition of salts (Ca, Mg, K, Na and inorganic phosphate) was determined experimentally by atomic absorption and emission spectroscopy, colorimetry and 31P-nuclear magnetic resonance spectroscopy, and calculated with a model of the salt partition in milk based on equilibrium thermodynamics. Hydrodynamic radius, skim milk viscosity and casein micelle medium resolution substructure were measured by dynamic light scattering, rheology, and small-angle X-ray scattering (SAXS), respectively. TG treatment of milk did not influence the partition of salts upon the addition of EDTA as TG crosslinking is unlikely to disrupt the phosphate centre motifs on the short exon-encoded amino acid sequences on caseins. However, TG treatment prevented full dissociation of casein micelles when >15 mM EDTA was added, and induced higher viscosity increase than TG-untreated milk upon addition of EDTA. In accordance with the particle sizing results, SAXS demonstrated that TG treatment reduced the extent of EDTA-induced micellar disruption, as compared to milk without TG treatment.