β-Casein micelles; cross-linking with transglutaminase

The association behaviour of β-casein was markedly affected by transglutaminase (TG)-catalysed crosslinking. Treatment of β-casein with TG at 35 °C eliminated the ability of β-casein micelles to monomerise on cooling, while β-casein pre-treated with TG at 0 °C was unable to associate into micelles when the temperature was increased to 40 °C. The effect of TG when incubated with β-casein at 35 °C is attributed to intermolecular crosslinking. While the effect of TG when incubated with β-casein at 0 °C is due to intramolecular crosslinking which inhibits micellisation by reducing molecular mobility and/or causes an alteration in the charge distribution of β-casein. The effect of TG treatment at 0 or 35 °C on some of β-caseinʹs physico-chemical properties (calcium sensitivity, hydrophobicity and viscosity) was studied and shown to be altered by TG treatment at both 0 and 35 °C. Changes in the physico-chemical properties of TG-treated β-casein appear to be due, in part, to charge modification.