Biology Reference
In-Depth Information
analysis of up to 300 polypeptide constituents in microliter
volumes of unconcentrated beer. However, protein identifi cation
was not possible in these earlier studies. Therefore, the species of
beer protein was unknown, and the information, whether it was
related to beer quality, was not clear from these studies.
2.2 Proteome Maps
of Beer and Wort
A specifi c protein profi le may be required in each beer type. Protein
profi les are infl uenced by barley grain (cultivars) and their malting
and brewing conditions. In addition, differences in beer and wort
quality profi les can be detected by the comparison of protein con-
centrations. Beer protein analysis started with one-dimensional gel
electrophoresis. The analysis of the protein profi le of oat wort, as
measured by using Lab-on-a-Chip analysis, revealed that there
were no signifi cant differences in the protein profi les between oat
and barley worts [
13
,
14
]. Bobálová et al. [
15
] analyzed barley
grain and malt proteins of two cultivars by SDS-PAGE and mass
spectrometry and found no signifi cant difference in the two culti-
vars tested. Hao et al. [
16
] analyzed beer and beer foam proteins
by SDS-PAGE and tandem mass spectrometry, and identifi ed 21
and 24 proteins in beer and beer foam, respectively. However,
these one-dimensional gel electrophoresis analyses did not have
enough resolution to compare the protein profi les of the samples.
2.2.1 One Dimensional
Gel Electrophoresis
Analysis of Beer Proteins
Two-dimensional gel electrophoresis (2DE) is more appropriate for
comparing proteomes because it has improved resolution in protein
detection compared with one-dimensional gel electrophoresis i.e.,
SDS-PAGE. In past decades, exponential improvement in mass spec-
trometry techniques such as matrix-assisted laser desorption ioniza-
tion (MALDI) and electrospray ionization (ESI) methods, and
peptide searching systems in protein and DNA databases led to the
identifi cation of protein species on a large scale. Though the barley
genome has not been completely sequenced to date, expressed
sequence tag (EST) and full-length cDNA sequences strongly sup-
port the protein identifi cation [
17
,
18
]. Based on the advancement
in these research tools, beer proteome analysis is progressing rapidly.
A proteome map, which displays identifi ed protein spots on a
2DE image, is a platform for analyzing beer proteins. Perrocheau
et al. [
8
] analyzed beer proteins by 2DE and mass spectrometry
and identifi ed 30 protein spots. Iimure et al. [
9
] identifi ed 85 pro-
tein spots on 2DE gel out of 199 spots, and categorized them into
12 protein species. Based on these proteome maps, they compared
the 2DE images of beer proteins, which were derived from malt
samples of different barley cultivars and malt modifi cations, and
found that the spot intensities of several beer-quality-related pro-
teins were different among the beer samples. Fasoli et al. [
19
]
identifi ed more beer protein species, especially proteins derived
from yeast using a unique technique as follows: they analyzed beer
proteomes through prior capture with combinatorial peptide
2.2.2 2DE and LC-MS/
MS Analyses of Beer
Proteins and Protein
Identifi cation
