  We use a coarse-grained model to study the conformational changes in two
barley proteins, LTP1 and its ligand adduct isoform LTP1b, that result from
their adsorption to the air-water interface. The model introduces the interface
through hydropathy indices. We justify the model by all-atom simulations. The
choice of the proteins is motivated by making attempts to understand formation
and stability of foam in beer. We demonstrate that both proteins flatten out at
the interface and can make a continuous stabilizing and denser film. We show
that the degree of the flattening depends on the protein -- the layers of LTP1b
should be denser than those of LTP1 -- and on the presence of glycation. It
also depends on the number ($\le 4$) of the disulfide bonds in the proteins.
The geometry of the proteins is sensitive to the specificity of the absent
bonds. We provide estimates of the volume of cavities of the proteins when away
from the interface.
