Novel Prediction Method of Beer Foam Stability Using Protein Z, Barley Dimeric α-Amylase Inhibitor-1 (BDAI-1) and Yeast Thioredoxin

Abstract

Foam stability is an important quality trait of beer. Our previous results of two-dimensional gel electrophoresis (2DE) analyses of beer proteins implied a relationship between barley dimeric alpha-amylase inhibitor-1 (BDAI-1) and beer foam stability as judged by the NIBEM-T analyzer. To develop a novel prediction method of beer foam stability under different conditions of barley cultivar and malt modification, multiple linear regression analysis was applied. The spot intensities of major beer proteins on 2DE gel were quantified and used as explanatory variables. The foam stabilities of 25 beer samples each brewed from malt with different malt modification in one of the three cultivars (cultivars A, B, and C) were explained by the spot intensities of BDAI-1 at the 5% significance level ( r = 0.421). Furthermore, two other major protein spots (b0 and b5) were observed on the 2DE gels of Japanese commercial beer samples with different foam stability. Then, multiple regression for foam stability was calculated using these three spot intensities as explanatory variables. As a result, 72.1% of the beer foam stability in 25 beer samples was explained by a novel multiple regression equation calculated using spot b0 and BDAI-1 as positive explanatory variables and spot b5 as a negative variable. To verify the validity of the multiple regression equation and the explanatory variables, the beer foam stability in practical beer samples was analyzed. As a result, 81.5% of the beer foam stability in 10 Japanese commercial beer samples was also explained by using spot b0 and BDAI-1 as positive explanatory variables and spot b5 as a negative variable. Mass spectrometry analyses followed by database searches revealed that protein spots b0 and b5 were identified as protein Z originated from barley and thioredoxin originated from yeast, respectively. These results confirm that BDAI-1 and protein Z are foam-positive factors and identify yeast thioredoxin as a possible novel foam-negative factor.

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

“…Proteolytic cleavage in the reactive site loop converts protein Z to a heat and protease stable form that can survive the brewing process. Multiple spots of protein Z have been observed on malt and beer 2D gels 67,78,79,130 . Protein Z contains 20 lysines per molecule; glycation occurs during the malting and brewing process and 16% of the lysine content has been found glycated upon brewing 70 .…”

“…Beer proteins from malting barley and the bitter substances from hops are essential for beer foam formation and stabilization, while lipids are detrimental 37 . Foam stability has been controlled by different foam promoting proteins from barley, as well as foam destabilizing ones from yeast 78,79 . Interactions of numerous foam influencing components are complex and the contribution of individual foam active proteins can be only evaluated in the context of the whole beer system.…”

“…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 .…”

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.…”