Probing heat-stable water-soluble proteins from barley to malt and beer

Abstract

Proteins determine the quality of barley in malting and brewing end-uses. In this regard, water-soluble barley proteins play a major role in the formation, stability, and texture of head foams. Our objective was to survey the barley seed proteins that could be involved in the foaming properties of beer. Therefore, two-dimensional (2-D) electrophoresis and mass spectrometry were combined to highlight the barley proteins that could resist the heating treatments occurring during malting and brewing processes. As expected, from barley to malt and to beer, most of the heat-stable proteins are disulfide-rich proteins, implicated in the defense of plants against their bio-aggressors, e.g., serpin-like chymotrypsin inhibitors (protein Z), amylase and amylase-protease inhibitors, and lipid transfer proteins (LTP1 and LTP2). For LTP1s, the complex pattern displayed in 2-D electrophoresis could be related to some chemical modifications already described elsewhere, such as acylation or glycation through Maillard reactions, which occur on malting. Our proteomics approach allowed the identification of the numerous proteins present in beer in addition to the major ones already described. The involvement of these proteins in the quality of beer foam can now be evaluated.

Differentially expressed genes during malting and correlation with malting quality phenotypes in barley (Hordeum vulgare L.)

“…It has been shown that the molds and bacteria in barley increase during malting, reaching a peak during the germination stage (Flannigan 2003), consistent with the observation that defense and stress response genes increased from steeping to day 4. Analysis of the proteome of malt and beer also showed the predominance of proteins involved in protection against pathogens and insects (Perrocheau et al 2005). In addition, seed germination may be considered a critical time point in a plant's life cycle and it is not surprising that a large number of defense-related genes are normally upregulated as a protective measure.…”

“…Other genes that were up-regulated from germination through kilning included those coding for peptidases, lipid transfer proteins, and proteinase inhibitors. These proteins were identiWed as thermostable components of malt and beer (Perrocheau et al 2005). Other genes that were up-regulated from germination to kilning were those for heat shock proteins, which function to protect enzymes during heat stress (Jinn et al 1995;Waters et al 1996).…”

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

“…A biphasic expression, similar to the expression of the TLP genes in barley and oat seeds 308 , has been reported for serpins 282 . Recent proteomics studies have confirmed the presence of high amounts of acidic proteins identified as protein Z in barley and malt, and a third isoform, Zx, which was not previously detected 247,260 . Analysis of the peripheral granule proteome in barley endosperm revealed only presence of BSZ4 27 .…”

“…They probably play a role in the dough aqueous phase and the dough's ability to form an elastic interface lining the bubbles, maintaining integrity during dough proving 291 . Proteomics has enabled the identification of CMs (CMb, BDAI-1, BTI-CMe2.1, BMAI-1) in beer 260 . These could affect beer foam quality and participate in haze formation.…”

“…Differences in the protein composition between barley varieties, as well as changes in seed protein composition during development and germination, and under different environmental conditions have been surveyed using proteomics 15,24,[86][87][88][89][90][91][92]202,247,248 . Recent proteomics studies of beer 260 , beer foam 118,243 and beer haze 139 enabled identification of proteins that may influence beer quality.…”