Chemistry Reference
In-Depth Information
Table 8.3
Enzymes whose production
is influenced by gibberellic acid.
Aleurone enzyme
α
-Amylase
Endo-
β
, 1,3:1,4 glucanase
Endoprotease
Pentosanase
Limit dextrinase
Cellobiase (
β
-glucosidase)
Laminaribiase
produce the enzymes associated with germination. The action of gibberellic acid in barley
is to increase the production of the messenger RNA, which is responsible for the formation
of specific enzymes, from the DNA of the aleurone cell nuclei. It does this by switching on
specific genes that had previously been suppressed by other substances.
8.2.2.1
Cell wall breakdown during germination
The cell walls in the starchy endosperm of the barley kernel comprise 75% β-1,3 β-1,4 glucan,
20% arabinoxylan and 5% protein, plus traces of other constituents such as acetic and ferulic
acids. The cell wall polysaccharides are detrimental to brewing performances if they are
not sufficiently hydrolyzed during malting and later again during mashing. A simple model
(Fig. 8.1) has been proposed
5
to explain both the structure of the barley cell wall and the range
Outer
Inner
Xylan
Arabinose
Glucan
Acetic
Ferulic
Barley cell wall composition:
-75%
β
-(1-3)(1-4)-glucan
- 20% arabinoxylan
- 5% protein
Trichoderma viride
mode of attack:
1.
Endoxylanase
2.
Carboxypeptidase
3.
Endo-b 1,4 glucanase, arabinofuranosidase,
xyloacetylesterase, feruloyl esterase
4.
Endo-barley-
β
-glucanase
Fig. 8.1
Model of barley cell wall structure, barley cell wall composition and Trichoderma viride mode
of attack (adapted from Ref. [5]).
