Environmental Engineering Reference
In-Depth Information
4.
Plant phytases
enous phytase activity were found in stomach
chyme and small intestine, though in the colon
the phytate hydrolysis was of an endogenous ori-
gin. Intestinal bacteria with endogenous phytase
activity were discovered in several species of
fish. Huang et al. (
2009
) screened the intestinal
contents of grass carp and found the phytate-
degrading isolates,
Pseudomonas
,
Bacillus
and
Shewanella
species.
Many plant seeds contain significant amounts
of phytic acid that is degraded during germina-
tion by one or more phytases. Seeds contain both
constitutive phytase activity and phytases that are
synthesised again during germination; however,
this last mechanism is not well understood. The
activity of phytase has been well reported from
Arabidopsis thaliana
AtPAP15 (Li et al.
2012
),
Glycine max
GmPhy (Hegeman and Grabau
2001
), and
Medicago truncatula
MtPHY1 (Xiao
et al.
2005
). The optimum temperature and pH
measured for most plant phytases ranges from
45 to 60 ﾰC and from 4.0 to 7.2 pH, respectively.
Alkaline phytases with unique catalytic proper-
ties have been identified in plants. Garchow et al.
(
2006
) purified alkaline phytase from pollen
grains of
Lilium longiflorum
. These investiga-
tors suggested that the unique properties of this
alkaline phytase attributed to it the potential to be
useful as a feed and food supplement.
7.4.2
Consideration in Use of Phytases
in Animal Feeds
Over the past 20 years, animal producers raised
the issues and interventions demanding a more ef-
ficient, economical and environmentally friendly
approach to the industry. Phytase supplementa-
tion to animal feed is an effective way of increas-
ing the availability of P to animals, thus improv-
ing their performance and reducing manure-
borne P pollution. In addition to its major appli-
cation in animal nutrition, phytase is also used for
processing of human food. Wodzinski and Ullah
(
1996
), recognised that the addition of phytase
to the diet of every monogastric animal reared in
the USA would not only diminish the P released
into the environment by 8.23 ￗ 10
7
kg, but also
would save the animal producers $ 1.68 ￗ 10
8
/
year in its supplementation. Since then, the use
of phytase as a feed additive has become widely
accepted and several commercial phytase prepa-
rations (e.g. Natuphos
TM
, Ronozyme P, Phyzyme
XP) are used in Europe and the USA (Selle and
Ravindran
2007
). From their commercialisation
in the early 1990s, the sales value for phytase
was estimated at $ 50 million within the decade
(Sheppy
2001
), where today it represents more
than half of all feed enzyme sales (< $ 250 mil-
lion) (Wyatt et al.
2008
).
Microbial phytase is one of the most com-
monly used enzymes in monogastric animal diets
(Shim et al.
2004
). Paik (
2003
) conducted a series
of experiments in broilers and layers to evaluate
the effects of microbial phytase on several miner-
als such as N, P, Cu, Zn and K and showed that the
dietary treatment could reduce P excretion enor-
5.
Animal phytases
The existence of the first animal phytase was
demonstrated in the blood and liver of calves in
1908
by McCollum and Hart. Since then, con-
troversy has persisted regarding the existence of
phytases in animals in the digestive tract of ani-
mals (especially monogastric animals). Accord-
ing to Rapoport et al. (
1941
), other investigators
failed to find phytase in the extracts of intestine,
pancreas, kidney, bone, liver and blood of sev-
eral species of animals. Preliminary work on the
activity of phytase produced by rumen microor-
ganisms was initiated by Raun et al. (
1956
) and
undertaken again by Yanke et al. (
1998
). They
further examined the presence of phytase activ-
ity in species of obligatory anaerobic ruminal
bacteria and concluded that the most highly ac-
tive strain was
Selenomonas ruminantium
. With
the objective of outlining the complete system of
phytate degradation in the gut of humans and the
enzymes involved, Schlemmer et al. (
2001
), car-
ried out a study using pigs as model for humans
and concluded that negligent amounts of endog-
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