Degradation of a Foam-Promoting Barley Protein by a Proteinase from Brewing Yeast

Impact of propagation time on yeast physiology during bottle conditioning of beer on an industrial scale

Bottle conditioning occurs when yeast and a fermentable extract are added to beer prior to packaging. Aside from ethanol and carbon dioxide production, this process can minimize the production of off-flavors and increase the shelf-life of beer. The advantages of bottle conditioning rely on the yeast being able to quickly referment the beer and maintain viability during storage. In this study, a commercial ale yeast was propagated in wort on a large scale (30 hL) for 24 h or 72 h and seeded into pale ale beer for bottle conditioning. We found that yeast propagated until the post-diauxic shift (72 h) provided better longevity in the bottle and improved foam stability compared to the 24 h propagated yeast. At the time of seeding, yeast propagated for 72 h showed an upregulation of proteins involved in cellular respiration and general stress pathways that may indicate responses toward mitigating cellular stress levels.

Effect of Addition of Different Phenolic-Rich Extracts on Beer Flavour Stability

Flavour stability is a key factor in the beer production process. The stabilizing effect of six commercial phenolic-rich extracts was studied. The extracts were added to beer before bottling. Quality parameters (colour, turbidity, foam and dissolved oxygen content), antioxidant activity by 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), total polyphenols content, and sensorial analysis by a trained panel were performed over the course of storage. The beers were analyzed every 3 months for a total period of 6 months. Results indicated that all studied phenolic-rich extracts positively affected the beer flavour stability. In particular, the condensed tannins showed a significant protective effect. The condensed green tea tannins resulted as the most promising source of natural antioxidant able to prolong beer shelf-life and bring interesting organoleptic characteristics to beer. Also, grape seed tannins appeared suitable to boost flavour stability and improve organoleptic properties of beer.

Cell-Free Identification of S. cerevisiae Strains by Analysis of Supernatant Using LC-MS

Current literature shows a gap for methods which can identify yeast sub-species (strains or serovars) in samples where there are no viable cells remaining. Presented here is a technique for the analysis of yeast supernatant, including solid phase extraction, data-dependent acquisition liquid chromatography/mass spectrometry (LC-MS), and two chemometric methods to identify and classify yeast strains. Five strains of Saccharomyces cerevisiae were successfully identified in various stages of growth. In addition, peptide/protein identification was performed, without the need for additional data acquisition. Graphical Abstract ᅟ.

Overview of Serpins and Their Roles in Biological Systems

Serine protease inhibitors are ubiquitous regulators for a multitude of pathways in humans. The serpins represent an ancient pathway now known to be present in all kingdoms and often regulating central pathways for clotting, immunity, and even cancer in man. Serpins have been present from the time of the dinosaurs and can represent a large proportion of circulating blood proteins. With this introductory chapter, we present an overview of serpins as well as an introduction and overview of the chapters describing the methodology used in the new approaches to understanding their molecular mechanisms of action and their roles in health and disease.

Structural Changes in Barley Protein LTP1 Isoforms at Air-Water Interfaces

We use a coarse-grained model to study the conformational changes in two barley proteins, LTP1 and its ligand adduct isoform LTP1b, that result from their adsorption to the air-water interface. The model introduces the interface through hydropathy indices. We justify the model by all-atom simulations. The choice of the proteins is motivated by making attempts to understand formation and stability of foam in beer. We demonstrate that both proteins flatten out at the interface and can make a continuous stabilizing and denser film. We show that the degree of the flattening depends on the protein (the layers of LTP1b should be denser than those of LTP1) and on the presence of glycation. It also depends on the number (≤4) of the disulfide bonds in the proteins. The geometry of the proteins is sensitive to the specificity of the absent bonds. We provide estimates of the volume of cavities of the proteins when away from the interface.

Beer and wort proteomics

Proteome analysis provides a way to identify proteins related to the quality traits of beer. A number of protein species in beer and wort have been identified by two-dimensional gel electrophoresis combined with enzyme digestion such as trypsin, followed by mass spectrometry analyses and/or liquid chromatography mass/mass spectrometry. In addition, low molecular weight polypeptides in beer have been identified by the combination of non-enzyme digestion and mass analyses. These data sets of various molecular weight polypeptides (i.e., proteomes) provide a platform for analyzing protein functions in beer. Several novel proteins related to beer quality traits such as foam stability and haze formation have been identified by analyzing these proteomes. Some of the proteins have been applied to the development of efficient protein or DNA markers for trait selection in malting barley breeding. In this chapter, recent proteome studies of beer and wort are reviewed, and the methods and protocols of beer and wort proteome analysis are described.

The impact of different ale brewer's yeast strains on the proteome of immature beer

Background

It is well known that brewer’s yeast affects the taste and aroma of beer. However, the influence of brewer’s yeast on the protein composition of beer is currently unknown. In this study, changes of the proteome of immature beer, i.e. beer that has not been matured after fermentation, by ale brewer’s yeast strains with different abilities to degrade fermentable sugars were investigated.

Results

Beers were fermented from standard hopped wort (13° Plato) using two ale brewer’s yeast (Saccharomyces cerevisiae) strains with different attenuation degrees. Both immature beers had the same alcohol and protein concentrations. Immature beer and unfermented wort proteins were analysed by 2-DE and compared in order to determine protein changes arising from fermentation. Distinct protein spots in the beer and wort proteomes were identified using Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and MS/MS and revealed common beer proteins, such as lipid transfer proteins (LTP1 and LTP2), protein Z and amylase-protease inhibitors. During fermentation, two protein spots, corresponding to LTP2, disappeared, while three protein spots were exclusively found in beer. These three proteins, all derived from yeast, were identified as cell wall associated proteins, that is Exg1 (an exo-β-1,3-glucanase), Bgl2 (an endo-β-1,2-glucanase), and Uth1 (a cell wall biogenesis protein).

Conclusion

Yeast strain dependent changes in the immature beer proteome were identified, i.e. Bgl2 was present in beer brewed with KVL011, while lacking in WLP001 beer.

Cloning and characterization of the beer foaming gene CFG1 from Saccharomyces pastorianus

Foam production is an essential characteristic of beer, generated mainly from the proteins present in the malt and, to a minor extent, from the mannoproteins in brewer's yeast cell walls. Here, we describe the isolation and characterization of the novel fermentation gene CFG1 (Carlsbergensis foaming gene) from Saccharomyces pastorianus. CFG1 encodes the cell wall protein Cfg1p, a 105 kDa protein highly homologous to Saccharomyces cerevisiae cell wall mannoproteins, particularly those involved in foam formation, such as Awa1p and Fpg1p. Further characterization of Cfg1p revealed that this novel protein is responsible for beer foam stabilization. This report represents the first time that a brewing yeast foaming gene has been cloned and its action fully characterized.

Evidence for an extracellular acid proteolytic activity secreted by living cells of Saccharomyces cerevisiae PlR1: impact on grape proteins

In this work, Saccharomyces cerevisiae PlR1, a strain isolated from Pinot noir grapes in the Champagne area, was shown to secrete an acid proteolytic activity against bovine serum albumin. This proteolytic activity was detectable in cell-free culture supernatants at the beginning of the exponential growth phase and increased with yeast growth. Using a zymography method, only one protease band with a molecular mass of 72 kDa was observed. This extracellular proteolytic activity was detected in the pH range from 2 to 4 with a maximal value at pH 2.5 and 38 °C and was completely inhibited by pepstatin A. The secretion of this protease did not need any protein inducer and seemed to be insensitive to nitrogen catabolic repression. S. cerevisiae PlR1 was also able to secrete this proteolytic activity during alcoholic fermentation, and it was found to be active against grape proteins, with a molecular mass around 25 kDa, at optimal conditions of 38 °C, pH 3.5.

Novel prediction method of beer foam stability using protein Z, barley dimeric alpha-amylase inhibitor-1 (BDAI-1) and yeast thioredoxin

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.

The influence of barley malt protein modification on beer foam stability and their relationship to the barley dimeric alpha-amylase inhibitor-I (BDAI-I) as a possible foam-promoting protein

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.