Biology Reference
In-Depth Information
Haze-related proteins have been analyzed using the proteome
approach. Haze-active proteins can be removed by physical treat-
ment, i.e., application of silica gel [
44
,
45
]
.
Therefore, brewers gen-
erally add silica gel during beer fi ltration to prevent beer colloidal
haze. Robinson et al. [
46
] prepared an antibody that specifi cally
bound to silica gel eluent proteins (SE proteins), and identifi ed tryp-
sin inhibitor CMe precursor (CMe) as a haze-active protein using
2DE and N-terminal sequence analysis of tryptic peptides. Iimure
et al. [
47
] analyzed four haze samples and SE proteins by 2DE and
mass spectrometry and suggested that BDAI-1, a component of tet-
rameric alpha-amylase inhibitor (CMb), and CMe were not predom-
inant haze-active proteins, but growth factors for beer colloidal haze.
In addition, Jin et al. [
48
] analyzed silica gel eluent proteins by 2DE
and mass spectrometry and identifi ed CMe, germin E, and protein Z
as possible haze-active proteins. Jin et al. [
49
] suggested that hordein
may be minor haze-active proteins but are crucial for haze formation
according to a 2DE analysis of malt, wort, and haze samples. Colgrave
et al. [
12
] quantifi ed the contents of hordein family proteins such as
avenin-like protein-a, B1-, B3-, D-, and
2.4.2 Beer Haze-Related
Proteins
-hordeins in commercial
beer samples by Multiple Reaction Monitoring (MRM) mass spec-
trometry. The hordein family contents in beer depended on the sam-
ples, suggesting that barley cultivar, malting, and brewing conditions,
type of beer, and adjuncts affected their contents. Polypeptides
derived from the hordein family have been suggested to be foam-
positive and haze-negative [
32
,
50
]. However, the relation between
hordein and foam quality has not been clarifi ed [
51
,
52
].
γ
A number of beer proteins and polypeptides have been identifi ed
[
8
-
12
,
19
], and these data form the basis of a strong platform for
further study of beer proteomes. Although several proteins related to
beer quality traits such as foam stability and haze formation have
been identifi ed, currently, the mechanism of the foam and haze for-
mation is still controversial. The objectives of beer proteome study
are identifi cation of quality-related proteins, detection of proteome
differences in malting and brewing conditions, and investigation of
proteome differences among barley cultivars. From this perspective,
however, beer proteome study is still at an early stage. As well as the
advancement of mass spectrometry, development of fractionation
methods of beer and wort proteins such as salt-precipitated proteins
[
35
], foam-concentrated proteins [
35
], silica gel eluent proteins [
46
-
48
], and prior capture using CPLL technology [
19
] are important to
detect objective protein species. In addition, collecting appropriate
samples that differ in the target quality trait is essential to identifying
the respective proteins. To apply the knowledge of beer and wort
proteomes in malting barley breeding, the genetic analysis of objec-
tive proteins is necessary as demonstrated by Robinson et al. [
46
]
and Iimure et al. [
28
]. From this perspective, proteomics must be
further improved according to the advancement of barley genomics.
