Modulation of hydrophobic interactions in denatured whey proteins by transglutaminase enzyme

The role of enzyme crosslinking in mediating formation of hydrophobic association in chemically denatured whey protein isolates (WPI) is examined. WPI samples denatured with dithiothreitol (DTT) and incubated at 50 °C with and without transglutaminase enzyme show dramatic differences in viscosity, with the viscosity of the sample exposed to enzyme being lower by several orders of magnitude than the sample without enzyme. Upon further exposure of both samples to sodium dodecyl sulfate (SDS) to eliminate hydrophobic interactions, we observe no change in the viscosity of the sample previously treated with enzyme, suggesting this sample to have minimal hydrophobic associations. In contrast, the sample without enzyme shows a dramatic drop in viscosity indicating it to have had substantial hydrophobic associations. A similar trend but to a lesser extent is observed at a higher WPI concentration. These results taken together suggest that the formation of enzyme catalyzed ε-(γ-glutamyl)lysine bonds attenuates hydrophobic interactions through steric hindrance and formation of compact molecules that limits exposure of the hydrophobic moieties.