Heat-Induced Changes in the Chemical Structure, Hydrophobicity, and Size Distribution of Free/Bound Lipid Transfer Protein 1 and Their Effects on Beer Foam

During brewing processes, proteins such as lipid transfer protein 1 (LTP1) are exposed to high temperatures, which later affects the beer foam properties. To develop high-quality beer, it is therefore essential to understand the protein chemical modifications and structural alternations induced by the high temperatures and their impact on beer foam. This study characterizes heat-induced chemical modifications and changes in the molecular size distribution and structure of LTP1 and its lipid-bound isoform, LTP1b, using size-exclusion chromatography and reverse-phase chromatography/mass spectrometry. The results elucidate the relationships between these changes and foam properties. Specifically, heat treatment triggers lipid adduct dissociation from LTP1b, increases the concentration of deamidated hydrophobic LTP1 molecules, and causes deglycation. Both the dissociation of lipid adducts from LTP1b and the increase in deamidated hydrophobic LTP1 molecules result in lower quality foam. Thus, controlling brewing processes, especially in terms of heating conditions, can effectively retain LTP1b to enhance beer foam.