Chromatography Reveals Protein Modifications Driving Foam in Beer

A joint study by The University of Osaka (Japan) andSuntory Global Innovation Center (Kyoto, Japan) analyzed heat-induced changes in lipid adducts, glycation, other post-translational modulations (PTMs), and the structures of liquid transfer proteins (LTP1) to reveal their effects on beer foam properties. Collected LTP1 and LTP1b (LTP1’s lipid-bound isoform) fractions were concentrated and further purified by a second size-exclusion chromatograph (SEC), and the PTMs and structural changes caused by the thermal stress were evaluated by liquid chromatography/mass spectrometry (LC–MS). A paper based on this research was published in the Journal of Agricultural and Food Chemistry (1).

One of the most widely consumed alcoholic beverages worldwide, the demand for superior beer continues to increase (2,3). The foam of the beverage has been a crucial element in the determination of whether a beer is high-quality (4,5). Foam enhances the flavor and mouthfeel of beer while shaping the expectations of the consumer through its visual appeal, as well as acts as a barrier against direct oxygen exposure, obstructing the oxidative deterioration of the beverage (6-10).

The adsorption of proteins at the air–liquid interface drives foam formation, playing an important role in foam stabilization (9,11). Intermolecular interactions among proteins also create interfacial films and enhance interfacial viscoelasticity, which stabilizes the foam (12-14). Of the four primary ingredients in beer (water, barley malt, hops, and yeast), proteins in beer some mainly from the barley malt (15).

The team’s analysis of heat-induced changes in lipid adducts, glycation, other PTMs, and the structures of LTP1 and LTP1b revealed their influence on properties of beer foam properties, as well as the important aspects of LTP1 and LTP1b regarding optimal foam quality. Heat treatment increased the hydrophobicity of LTP1 molecules and induced various PTMs (deglycation, lipid adduct dissociation, and deamidation). Prior to heating, While LTP1b showed superior foam properties compared to LTP1 prior to heating, these properties significantly decreased after heating, primarily due to increased hydrophobicity and lipid adduct dissociation. In addition to deglycation, the brewing process produced other chemical modifications and increased protein hydrophobicity at a similar rate to those seen in the heat-treated purified LTP1 and LTP1b samples. The examination of samples which were taken directly from the brewing process implied that interactions with hop- or yeast-derived compounds may stimulate the creation of additional hydrophobic LTP1 molecules (1).

The researchers believe that their results clarify the relationships between changes in the molecular size distribution and structure of LTP1 and its lipid-bound isoform, LTP1b, and the properties of the resulting beer foam. Heat treatment triggers lipid adduct dissociation from LTP1b, increases the concentration of deamidated hydrophobic LTP1 molecules, causing deglycation. Both the dissociation of lipid adducts from LTP1b and the increase in deamidated hydrophobic LTP1 molecules result in lower quality foam. Controlling brewing processes, especially in terms of heating conditions, can effectively retain LTP1b to enhance beer foam. Future efforts by beer brewers should concentrate on the optimization of boiling conditions (for example,, pH, temperature, and duration) and analysis of the effects to determine maximum brewing conditions for the making of beer with high foam quality (1).

References

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