Degradation of a foam-promoting barley protein by a proteinase from brewing yeast

The degradation of a major protein component in beer, the lipid transfer protein (LTP1), by the yeast proteinase A was determined. Another major protein fraction in beer, the protein Z-fraction, was not degraded by this enzyme. Protein preparations from beer and barley containing LTP1 were examined for degradation by proteinase A using SDS-PAGE, immunoblotting and RP-HPLC. LTP1 from barley was completely resistant to proteinase A, whereas LTP1 concentrated from beer was cleaved. We conclude that LTP1 was modified during the brewing process, thus rendering it more susceptible to proteinase A degradation.