new thermostable enzyme

1. AllAboutFeed.net - Vol 1 - Nr 5 - 2010
nutrition
New thermostable enzyme
helps meet demands for
safer feed
A new xylanase enzyme, developed by Danisco, has recently
been authorised by the EU commission for use in poultry
diets. This xylanase comes from a fungal production system
(Trichoderma reesei) and has been modified to maintain high
efficacy despite exposure to feed conditioning and pelleting
temperatures of up to 90º
C.
By Gwendolyn Jones,
Global Technical Manager,
Danisco, UK
Increasing pressure over feed safety
concerns and Salmonella control has
increased the need to use heat in pellet-
ing poultry feed. However, this is rarely
in favour of feed efficiency and bird
performance since it will increase the
viscosity of diets based on grains such
as wheat, triticale and barley. The use
of a heat-stable xylanase can reduce
the negative effects of increased viscos-
ity in poultry diets pelleted at 90º
C.
The effect of heat on feed efficiency
High processing temperatures can in-
activate endogenous enzymes in the
grains used in diets; potentially reduce
levels of certain vitamins; and poten-
tially reduce the availability of protein
and starch. Furthermore, increasing the
conditioning temperature above 80º
C
increases the viscosity of the diet and,
consequently, gut viscosity in the bird,
which will negatively interfere with the
digestion and absorption of nutrients
and increase the incidence of sticky
droppings (Table 1). Trials have shown
There are two options to protect an enzyme against high feed processing temperatures, namely coating
(Phyzyme TPT, pictured), or modifying the amino acid structure to improve thermostability

2. AllAboutFeed - Vol 1 - Nr 5 - 2010
that increasing the pellet condition-
ing temperature for poultry diets from
80º
C to 90º
C in ‘viscous’ grain-based
diets resulted in a significant decrease
in body weight gain by up to 7%, and
gave a poorer feed conversion ratio
(4.4%) in broilers.
Grains like wheat and barley contain
significant amounts of non-starch
polysaccharides (NSPs). Soluble arab-
inoxylans are the main NSPs in wheat
which increase the viscosity of the di-
gestive contents in the small intestine.
The heating process during pelleting
solubilises even more arabinoxylans,
which further increases the viscosity.
Apart from the direct physical ef-
fects of viscosity in the gut, increased
viscosity has a number of indirect
negative effects on the nutritive value
of poultry diets. These effects include
reduced rate of feed passage, increased
water consumption, and changes in
the gut microflora. A slower feed pas-
sage rate in the gut can also create an
environment that allows pathogenic
bacteria to multiply.
Xylanases increase feed efficiency
The arabinoxylan in wheat is a sub-
strate for the enzyme xylanase, which
will degrade arabinoxylans, and there
is much data to show that the enzy-
matic digestion of NSPs in poultry
diets will lead to reduced gut viscosity
and increased performance in birds.
The addition of xylanase increases the
energy value of wheat-based diets. It is
therefore particularly important when
formulating diets using viscous grains
such as wheat, triticale and rye that an
exogenous xylanase is used to mini-
mise the negative impact of viscosity
on bird performance.
Enzymes, however, are made of protein
and are therefore sensitive to excessive
heat. Enzymes differ in their intrinsic
resistance to heat inactivation. Once
the optimum temperature for a specific
enzyme has been reached, increasing
the temperature further, particularly in
conjunction with extended conditioning
times, can cause denaturing of the en-
zyme structure and thus irreversible loss
in activity. Any exogenous xylanase has
to be stable enough under higher pellet-
ing temperatures to maintain its activity
and efficacy in the animal.
Designing heat-stable xylanases
There are two ways of making enzymes
more heat-stable. One approach is to
use a coating to protect the enzyme;
the other is to manipulate enzymes into
more thermostable variants by chang-
ing their amino acid structure. Both
technologies have been found to sig-
nificantly improve enzyme stability and
have been successfully used to produce
commercial products.
A good coating needs to protect the
enzyme molecule through the feed
manufacturing process, but also needs
to release the product very quickly in
the upper part of the gut to ensure that
optimum efficacy is achieved. Achiev-
ing the correct balance poses a big
challenge for enzyme manufacturers as
in vitro studies have clearly shown dif-
ferences between products in the speed
at which they can release the active
enzyme. Danisco has used a patented
Thermo Protection Technology (TPT) to
design a free-flowing, dust-free phytase
granulate product (Phyzyme XP TPT)
with a recovery rate of 96% after expo-
sure to feed pelleting temperatures of up
to 95º
C. Trials have proven a fast release
of phytase activity from this coated
product and bioefficacy equivalent to
the uncoated product in mash diets.
The second technology, modifying an
enzyme by changing its amino acid
structure to improve thermostability,
has been widely tested in recent years.
This technique includes the substitution
of surface amino acids in the enzyme
with more hydrophobic amino acids,
as well as an increase in the number of
specific amino acids that are capable of
forming cross-bonds within the enzyme
molecule. It is this approach that Da-
nisco has chosen for the development
of the new xylanase.
Tests run at the Danish Technologi-
cal Institute at Kolding have shown
that the recovery rate of this enzyme
in pelleted feed samples was 80% at
90º
C (Figure 1). Danisco also provides a
service to its customers based on a soft-
ware programme (Avicheck), which de-
termines the most cost-effective dose of
this xylanase according to the viscosity
of the grain used in the diet. AAF
Table 1 - Properties of gut contents in broilers fed pelleted diets based on 77% wheat or barley,
either non-heat-treated or pelleted at 90º
C.
Barley Wheat
Non-heated Heat treated Non-heated Heat treated
Jejunal viscosity (cPs) 26.6b
80.8a
15.4b
30.2a
Dry matter in digestive 18.0a
16.6b
25.0a
19.8b
contents (%)
Faecal stickiness score* 2.9b
3.8a
2.9b
3.2a
*Subjective score of cage dirtiness, 5 for the dirtiest cage
a,b means P0.05 (Svihus 2006, Norwegian University of Life Sciences)
Figure 1 – Recovery rate of xylanase tests run at the Danish Technological Institute, Kolding,
Denmark. Pelleted feed processed at 80, 85 or 90º
C; steam conditioning time: 30 seconds; inlet steam
pressure: 2 bar (29 psi); pellet diameter: 3mm.
80o
C 85o
C 90o
C
No. samples (18) (21) (25)
91% 87% 80%