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16th Annual ASA-IM SEA Feed Technology and Nutrition Workshop

May 26-30, 2008 ♦ The Regent ♦ Singapore

Paper by Michael Bedford 3

Coating technologies improve thermotolerance of an enzyme by separating the enzyme

from the combination of heat and moisture of the pelleting process. Many enzymes arecapable of enduring high temperatures in the absence of moisture. Reducing simultaneous

exposure of the enzyme to “active water” and high temperatures by use of polyols or 

carbohydrates has been shown to be effective in improving thermostability of phytases,xylanases and amylases (De Cordt et al., 1994; George et al., 2001; Brugger et al., 2001).

The more obvious method of separating the enzyme from the environment through use of 

an encapsulating, hydrophobic coat has proved successful in enhancing thermotolerance

of enzymes (Klein Holkenborg & Braun, 2001)although such methods have also beenrelease may vary with different coating technologies, with some claiming no significant

delays at all (Owusu-Asiedu et al., 2007) although the experimental design used in such

trials (see issues below) does not always allow for confidence in the conclusions drawn.

 Nevertheless any effective coating will result in some initial delay in the release of theenzyme. Such delay may be of far greater significance for products which only act

in the upper intestinal regions than perhaps for those that work more later on. In thisregard coatings will have a greater significance for phytases than perhaps NSP’ases.

 Issues

Proof that an enzyme can survive the pelleting process is easily demonstrated through useof an appropriate assay. The ideal is that sufficient enzyme activity remains after the

 pelleting process to justify the nutrient matrix applied. For example, with phytases, the

nutrient matrix most often applied relates to the application of 500 units of enzyme per kgfeed. Provided the end user can find 500 units then the matrix applied is justified. The

 product used may guarantee delivery of 500 units post pelleting at a given temperatureeither through true thermo stability (ie 500 units applied and 500 recovered) or throughoverage (ie 1000 units applied, 50% lost in

 pelleting leaving 500 units) or a combination of both. As far as the end user is concerned,

either route results in the same outcome. It is not only essential that sufficient units of activity survive the pelleting process but also that the enzyme is active in vivo.

In consideration of coating, there is a fine balance between ensuring that sufficient is

applied to protect the enzyme from heat stress without compromising the ability of the

formulation to release activity rapidly in the animal.In assessing these properties of a coated enzyme, there are two errors that are often

encountered in trials which claim to demonstrate the efficacy of a coating

.1. The first is that the extent of the nutrient deficiency of the negative control is often not

well defined. Even inclusion of a positive as well as a negative control does not give

evidence as to the degree of deficiency of the negative control. For example, a test todemonstrate that 500 units of phytase is thermostable might employ a positive control

and negative control diet formulated to be 0.15% deficient in AvP. However, it is

 possible, due to ingredient variation, that the diet may actually be only 0.05% deficient

in AvP. If this were the case then as little as 200 units of phytase (ie 40% recovery)

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should easily equilibrate the performance of the negative with the positive control. The

 best solution in this case is to include several treatments which employ incremental doses

of an inorganic phosphate source so that the point at which AvP is no longer deficientcan be determined. Alternatively, a series of incremental doses of post-pellet liquid

applied phytase on the negative control would also demonstrate the optimum inclusion

level of units of phytase, beyond which further improvements become difficult to detect.In the example quoted above, if application of 500 units of the “thermotolerant” enzyme

through the conditioner/pellet press equilibrated performance with the positive control as

did 200 units of phytase applied post pellet, then the only conclusion that can be drawnis that at least 200 units of the thermo tolerant enzyme survived the pelleting process.

Similarly, any work using mash diets to demonstrate that a coating releases the enzyme

rapidly must demonstrate that at least the same dose of the uncoated enzyme is required

to achieve the same response, and that performance suffers if slightly less of the uncoated product is added

2. Comparisons of the efficacy of a coated enzyme sent through a conditioner / pellet

 press with enzymes fed in mash form cannot draw any conclusions. This is because the

subsequent performance of the animal is dependant as much on the amount of enzymedelivered to the animal as it is on the effect of diet form on intake. Moreover, if a given

dose of a coated form put through a pellet press is compared to a similar dose fed in amash diet, there is a possibility that both routes fail to deliver the target dose to the same

extent but for different reasons– e.g. a similar number of units of enzyme fail to release

from the product in mash diets as is thermally destroyed during the process of making

the pelleted diets

More recently, specifically in the case of phytase, it has also been recognised that gastric

stability is key to consistency in response

Feed composition also plays an important role in phytase stability. The feed composition

has an influence on friction heat and in some way on the residence time in the die, so theinfluence of the fat or fibre content on the activity loss cannot be overlooked (Eeckhout,

1999).