Beer foam is a key quality attribute that greatly influences consumer perception and overall beer quality. Proteins play an important role in foam stabilization. Foam formation is driven by protein adsorption at the air–liquid interface, while intermolecular interactions among proteins form interfacial films that enhance viscoelasticity and stabilize the foam. Lipid transfer protein 1 (LTP1), a lipid-binding protein abundant in the aleurone layer of the barley endosperm, comprises eight α-helices that confer high structural stability and prevent precipitation even after boiling during brewing. However, exposure to high temperatures can alter the structure and chemical state of LTP1, ultimately affecting foam properties. Therefore, understanding how heat-induced modifications of LTP1 influence foam stability is essential for producing high-quality beer.

In this study, heat-induced chemical modifications and changes in molecular size distribution and structural characteristics of LTP1 and its lipid-bound isoform, LTP1b, were analyzed using size-exclusion chromatography and reverse-phase chromatography coupled with mass spectrometry. Heating caused lipid adduct dissociation from LTP1b, increased the proportion of deamidated hydrophobic LTP1 molecules, and induced deglycation. Both lipid dissociation and the accumulation of hydrophobic LTP1 molecules were associated with reduced foam quality, indicating that precise control of heating conditions during brewing is critical for retaining functional LTP1b and enhancing foam stability.

We further examined the role of LTP1/LTP1b in the complex beer matrix and monitored their changes throughout the brewing process. LTP1b concentration of commercial beers was 0 to 0.1 µM, and a positive correlation was observed between LTP1b content and foam stability. Supplementation with purified LTP1b improved foam stability more effectively than LTP1; however, LTP1b was added together with other barley proteins, the improvement was limited, suggesting that the relative abundance of LTP1b within the total protein content also affects foam stability. Comparisons among barley cultivars showed that those with higher lipoxygenase (LOX) activity, which is an enzyme involved in LTP1b formation, contained higher levels of LTP1b. Therefore, using barley with lower LOX activity may result in poor beer foam quality. Analysis of samples collected during brewing revealed a reduction in LTP1b during boiling, consistent with results obtained from purified samples, although deglycation was not detected in beer samples. Overall, this study clarifies the molecular basis of LTP1-mediated foam stabilization and offers practical guidance for optimizing both raw material selection and brewing conditions to produce superior beer foam quality.

Reference: Mizuguchi J, Asaka K, Konishi M, Inui T, Uchiyama S, Torisu T. Heat-Induced Changes in the Chemical Structure, Hydrophobicity, and Size Distribution of Free/Bound Lipid Transfer Protein 1 and Their Effects on Beer Foam. J Agric Food Chem. 2025 Sep 24;73(38):24343-24353