Biology Reference
In-Depth Information
Reduction of disulfi de bonds in barley grain, malt, and beer were
surveyed by 2DE using the labeling of free thiol groups of water-
soluble heat-stable proteins including LTP1 [
33
]. These results
suggested the presence of free cysteine in malt and beer LTP1 but
not in that of barley. In a very recent paper [
34
], differences in
protein compositions of beer brewed from protein Z4 defi cient,
protein Z7 defi cient, double defi cient, and control barleys were
detected by 2DE. The spots with different intensities among the
beer samples were analyzed by matrix-assisted laser desorption ion-
ization time-of-fl ight/time-of-fl ight mass spectrometry (MALDI
TOF-TOF MS), resulted in the identifi cation of lipid transfer pro-
tein 2 (LTP2). Iimure et al. [
23
] detected protein Z in sweet wort,
boiled wort, and trub by 2DE, MALDI TOF-MS, and LC-MS/
MS, and found that protein Z was precipitated during wort boiling
by binding to comparatively small specifi c fragment(s) derived
from the sweet wort protein, i.e., barwin.
Several novel foam-related proteins were identifi ed by beer
proteome analysis. In general, beer foam stability decreases by
increasing malt modifi cation. Okada et al. [
35
] found that foam
stability of beer samples brewed from malts of two Japanese bar-
ley cultivars decreased as the level of malt modifi cation increased,
however, the foam stability of a Canadian barley cultivar tested
stayed at a higher level. To identify the protein responsible for the
foam stability of the Canadian cultivar, three fractions of beer
samples namely beer whole proteins, salt-precipitated proteins,
and the proteins concentrated from beer foam were analyzed by
2DE and mass spectrometry. As a result, barley dimeric alpha-
amylase inhibitor-1 (BDAI-1) was identifi ed as a foam-positive
protein. They also found that beer protein composition depends
much on the barley cultivar and malting condition such as the
ex-steep moisture level. Iimure et al. [
36
] analyzed all-malt, stan-
dard (67 % of malt in total raw materials), and low malt (Happoshu:
below 24 % of malt in total raw materials) beer samples with dif-
ferent foam stability using 2DE and mass spectrometry, and
found that yeast thioredoxin was identifi ed as a possible foam-
negative protein. Proteinase A from yeast is well known as a foam
negative factor [
37
-
39
]. Iimure et al. [
36
] fi rst identifi ed yeast
thioredoxin as a foam-negative protein, other than proteinase A.
Yeast thioredoxin is reported to be an intracellular protein [
40
,
41
]; however, the identifi cation of thioredoxin in beer suggested
that yeast cells were damaged during brewing. In addition, sev-
eral beer proteome analyses revealed that some yeast intracellular
proteins such as enolase and triose-phosphate isomerase were
contained in beer [
8
-
11
,
19
]. Beer foam stability and fl avor sta-
bility were also affected by the physiological condition of the
yeast cells [
42
,
43
]. These yeast proteins could be effective mark-
ers for controlling the physiological condition of brewing yeast in
terms of stability in beer foam and fl avor.
