Chemistry Reference
In-Depth Information
Table 8.2
(Continued)
Enzyme
Substrate
Activity
Source
Significance
Endo-
β
-glucanase
Solubilized
β
-glucan
Mixed linkages
Aleurone
Reduces wort
viscosity. Improves
mash filtration and
final beer filtration
Endopeptidase
Insoluble
hordein
Cleaves protein
chains
Aleurone
Breaks protein
matrix around
starch grains.
Improves mash
extraction. Improves
foam stability
Exopeptidase
Soluble
oligopeptides
derived from
hordein
Remove amino acids
from ends of peptide
molecules
Detectable in raw
barley
Carboxypeptidase
amino acids for
barley embryo and
eventually yeast
growth
Present prior to
germination
β
-Amylase
Starch grains
α
-1,4 linkages (two
glucose units at a
time from the end of
the chain)
Detectable in raw
barley
Rapid starch
solubilization
Present prior to
germination
Improves
fermentability
α
-Amylase
Starch grains
Starch internal
α
-1,4
linkages
Aleurone
Fermentability
α
-Glucosidase
Starch
α
-1,4 linkages
Detectable in raw
barley
Fermentability
α
-1,6 linkages
Some present prior
to germination, but
most from aleurone
Limit dextrinase
Starch
Cleaves amylopectin
α
-1,6 linkages
Detectable in raw
barley
Fermentability
Some present prior
to germination, but
most from aleurone
a
Many other endogenous enzyme reactions occur during malting which involve acid and alkaline phosphatases,
peroxidases, catalases, polyphenolicoxidases, lipoxygenase, phospholiases, phytase and others.
induced cell wall breakdown. Cell wall breakdown will be discussed in more detail later in
the chapter.
During germination, endogenous enzymes (Table 8.3), some directly influenced by phy-
tohormones such as gibberellic acid (GA3), hydrolyze proteins, β-glucans, arabinoxylan
and hemicellulose in the barley cell wall. The main effect of gibberellic acid is to stimulate
enzyme development within the aleurone of the germinating barley. Gibberellins are one
of the five main groups of hormones that coordinate plant growth. As well as affecting the
growth of mature plants, gibberellins are vital for germination of seeds. One of the first
responses of the embryo, once it is hydrated sufficiently, is the production and secretion of
gibberellins. These diffuse to the aleurone cells, via the scutellum, which are stimulated to
