Crosslinking of Casein Components by Transglutaminase

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Abstract
Transglutaminase catalyzes the formation of ε-(γ-glutamyl)lysyl crosslinks and the substitution of a variety of primary amines for the γ-carboxyamide groups of protein-bound glutaminyl residues. As a first step in the use of transglutaminase for enzymic modification of food proteins, the reactivity of bovine casein components (αs1-, β-, and κ-caseins) in the transglutaminase reaction was compared, and the properties of casein modified by this enzyme were examined. The reactivity of κ-casein was lower than that of αs1 or β-caseins. Sodium dodecyl sulfatepolyacrylamide gel electrophoresis analysis indicated that each casein component was polymerized through formation of intermolecular crosslinks by transglutaminase. Ultracentrifugal experiments in the absence of calcium ions revealed that complex formation between αs1-casein (or β-casein) and κ-casein was not impaired by this modification. The functional properties of αs1- and β-caseins in the presence of calcium ions (e.g. precipitation and micelle formation) were essentially retained after the modification. These results suggest that transglutaminase would be a useful tool to polymerize casein without damaging its special properties.