Interfacial properties and interaction between beer wort protein fractions and iso-humulone.

It is well known that both protein and iso-humulone, originating from barley malt and hops respectively, play important roles in beer foam stability. In this study, we hypothesize that the interaction of iso-humulone and different beer proteins will give rise to adsorbed layers with different characteristics at hydrophobic surfaces. The properties of these adsorbed layers are likely to play a crucial role for beer foam formation and stability. Beer protein and iso-humulone were extracted based on the brewing process from barley malt and hop respectively. The proteins were fractionated into two fractions (lipid transfer protein (LTP) and a mixed fraction of LTP and protein Z) and their interfacial properties as well as interaction with iso-humulone in solution and at hydrophobic surfaces were investigated by surface rheology and ellipsometry. The results show that the composition and properties of the adsorbed layers depend on how the layer is formed and that iso-humulone plays an important role for the characteristics of the adsorbed protein layers. The interaction between iso-humulone and protein Z is found to have pronounced effects of yielding a coherent and elastic adsorbed layer and, thus, for beer foam stability. Image 1 • Synergistic effects on surface pressure and dilatational moduli from wort proteins. • Iso-humulone and protein Z interaction leads to increased dilatational moduli. • Iso-humulone disrupts lipid transfer protein layers, decreasing dilatational moduli. [ABSTRACT FROM AUTHOR]