The Influence of Barley Malt Protein Modification on Beer Foam Stability and Their Relationship to the Barley Dimeric α-Amylase Inhibitor-I (BDAI-I) as a Possible Foam-Promoting Protein

Abstract

The foam stability of beer is one of the important key factors in evaluating the quality of beer. The purpose of this study was to investigate the relationship between the level of malt modification (degradation of protein, starch, and so on) and the beer foam stability. This was achieved by examining foam-promoting proteins using two-dimensional gel electrophoresis (2DE). We found that the foam stability of beer samples brewed from the barley malts of cultivars B and C decreased as the level of malt modification increased; however, the foam stability of cultivar A did not change. To identify the property providing the increased foam stability of cultivar A, we analyzed beer proteins using 2DE. We analyzed three fractions that could contain beer foam-promoting proteins, namely, beer whole proteins, salt-precipitated proteins, and the proteins concentrated from beer foam. As a result, we found that in cultivar A, some protein spots did not change in any of these three protein fractions even when the level of malt modification increased, although the corresponding protein spots in cultivars B and C decreased. We analyzed these protein spots by peptide mass finger printing using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. As a result, all of these spots were identified as barley dimeric alpha-amylase inhibitor-I (BDAI-I). These results suggest that BDAI-I is an important contributor to beer foam stability.

125th Anniversary Review: The Non-Biological Instability of Beer

“…In terms of protein Z, it seems that the Z4 component correlated with improved foam performance, whereas the reverse was observed for protein Z7 65 . It has been suggested that protein Z and an α-amylase inhibitor correlate positively with foam whereas yeast-derived thioredoxin was possibly foam negative 66,107 . The foam stability due to proteins reflects a balance between the respective levels of polypeptides derived from hordein and the albuminoid polypeptides Z and LTP1 17 .…”

A Review: The Role of Barley Seed Pathogenesis-Related Proteins (PRs) in Beer Production

“…BDAI-1, α-amylase/trypsin inhibitors CMb, probable trypsin-inhibitor CMe2.2, BMAI-1, α-amylase tetrameric inhibitor CMa and subtilisin-chymotrypsin inhibitor CI-1A have been identified in twice-foamed foam 67 . Among them, only BDAI-1 has been recognized as a foam-promoting protein 78,124 . The foam stability of different beer samples and comercial lager beers has been described by their levels of protein Z and BDAI-1 78 .…”

“…The majority of the beer proteins have been identified as PRs 67,79,130 . Proteome maps have also been used in beer quality control to associate particular beer proteins and respective beer quality traits [77][78][79]124 .…”

“…Beer foam, one of the most important aspects of beer quality, is determined by PRs. They play a major role in the formation, stabilization and retention of foam 37,60,124 . PRs may influence brewer's yeast fermentation 26,27,54,[57][58][59][60] .…”

A Review: Biological and Technological Functions of Barley Seed Pathogenesis-Related Proteins (PRs)

“…These could affect beer foam quality and participate in haze formation. BDAI-1 is assumed to be a foam promoting protein 140,243 , while BTICMe influences beer haze stability [284][285][286] . A proteomics study by Iimure 139 suggests that BDAI-1, CMb and CMe are growth factors of colloidal haze.…”