Poor foam stability in gluten-free beers is associated with distinct protein composition compared with barley-malt beers

Why was the work done?: Gluten-free (GF) beers typically exhibit poorer foam stability than conventional barley malt-based beers, yet the molecular basis underlying this difference remains poorly understood. This study aimed to investigate protein-level factors associated with foam stability in GF and barley beers. How was the work done?: Three commercially produced GF beers, comprising two lagers brewed from rice or sorghum, and one pale ale brewed from a millet-buckwheat-rice blend, were compared with two commercially produced barley-malt beers, comprising a lager and a pale ale. Soluble protein was isolated from freeze-dried beer powder using TCA-acetone. Protein profiles were examined using SDS-PAGE, and proteomes were characterised and compared using label-free quantitative LC-MS/MS. What are the main findings?: GF beers showed lower soluble protein concentrations and significantly lower foam stability than the barley beers. SDS-PAGE revealed fewer and weaker protein bands in GF beers compared with barley beers. Proteomic analysis showed that barley beers were enriched in known foam-active proteins, particularly lipid transfer protein 1 (LTP1) and Protein Z (serpin family members), whereas these proteins were not detected or were detected only at very low levels in GF beers.