Environmental Engineering Reference
In-Depth Information
last 20 years, interest in phytases has increased re-
markably, not only because of its wide range of ap-
plications in animal and human nutrition, but also
in response to heightened concerns over phospho-
rous pollution in the environment (Lei and Porres
2003
). Suzuki et al. first detected phytase activ-
ity in rice bran in 1907, but it was not until 1991
that the first phytase feed enzyme became com-
mercially available (Haefner et al.
2005
; Cao et al.
2007
). Phytase can be found in plants, bacteria,
fungi, yeast and animals. However, among mi-
croorganisms phytase activity has been observed
most commonly in fungi, particularly in
Aspergil-
lus
species (Kim et al.
1998
). Until now, a number
of phytase producing organisms have been re-
ported, but the search for a thermostable and acid-
stable phytase with broad substrate specificity and
high specific activity has been under progress for
animal nutrition purposes. The aforementioned
parameters were considered as key factors in the
use of phytase for animal nutrition. Additionally,
the low yield and high cost of enzyme produc-
tion are major limiting factors in use of phytase
enzyme in animal diet.
In this chapter, importance of P and phytic
acid in agriculture and animal nutrition leading
to P pollution is outlined. The consequences of
P pollution are discussed. Further, an insight in
phytases from different sources and various con-
siderations during their uses in phytic acid re-
moval and environmental pollution management
are discussed for better understanding and imple-
mentation of future strategies.
and micro-organisms, soil organic matter etc.).
Both forms of P are interconvertible with the aid
of soil bacteria and growing plants (Magette and
Carton
1996
). Mineral soil contains 33-90 % of
total P in inorganic form. In common with other
major elements, the concentration of total P in
soils is relatively higher considering the crop re-
quirements and available P fraction. The typical
range for total P content of agricultural soils is
estimated between 0.20 to 2.0 g/kg. Dissolved P
is typically less than 0.1 % of the total soil P and
usually exists as orthophosphate ions, inorganic
polyphosphates and organic P (Magette and Car-
ton
1996
).
In animal nutrition, P plays a key metabolic
role with more physiological functions than
any other mineral. These functions include P
as a major constituent of nucleic acids and cell
membranes, major constituent of the structural
components of skeletal tissues (80 % P found in
the bones and teeth), and is directly involved in
all energy-producing cellular reactions, mainte-
nance of osmotic pressure and acid-base balance,
protein synthesis, transport of fatty acids, amino
acid exchange, growth and cell differentiation,
appetite control, efficiency of feed utilisation and
fertility (NRC
1993
; Dobrota
2004
). The P nu-
tritional requirements for most farm animals are
well documented (dairy cattle 85-95 g/day, beef
cattle 35-40 g/day). The variation in P content
of natural feed has been observed in plants at
the species level. For example, the P content of
barley, maize and oats is very low compared to
rape seed meal. The P present in animal diet is
digested and metabolised differently by ruminant
and monogastric animals (Bomans et al.
2005
). P
deficiency in animal diet can affect the animal's
physical well-being including compromise of the
immune system, bone breakage, loss of appetite,
reduction in fertility and loss in live weight gain
due to low feed efficiency (Aehle
2007
). Diets
with low P content can be considerably improved
by the use of P feed supplement in the form of
compound feed or as separate mineral supple-
ments. P supplements are manufactured in many
chemical and physical forms to suit different
feeding and handling practices (http://www.nhm.
ac.uk/mineralogy/phos/) (Bomans et al.
2005
).
7.2
Importance and Need of P
in Animal and Plant Nutrition
7.2.1
Phosphorous: A Vital Source
of Animal Nutrition
Phosphorus is the 11th most abundant element on
earth. It exists in soil either in dissolved (i.e. solu-
tion) or solid form (particulate P), the solid form
being dominant. In solid form, P is classified as
inorganic P (P bound to Al, Fe, Ca, Mg etc. as
complex salts) and organic P (P bound to organic
material such as dead and living plant material
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