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Increases extrusion capacity and minimizes total operating and capacity-related costs.
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One of the most important and costly steps in dry pet food production is extrusion, during which the starch gelatinizes and becomes readily available to both cats and dogs. As cats and dogs are carnivores, they cannot digest raw starch, which is why the starch has to be thoroughly gelatinized during the extrusion step.
When starch gelatinizes, it forms an elastic, inflatable mass, which allows the food mass to expand upon discharge as water evaporates when pressure is released. On the other hand, when starch gelatinizes, the viscosity increases and the resistance at the die increases. Thus, the capacity of the extrusion process may be affected.
In some cases, the extruder capacity may vary by +/- 50% depending on food formulation, extrusion conditions and the size and shape of the kibbles. This variance in capacity may be minimized and overall extrusion capacity increased by approximately 25% if a Novozymes amylase is applied during preconditioning and extrusion. This increase is achieved without an ultimate increase in the energy requirement.
Depending on factory-specific circumstances, the savings in operating costs would normally be in the 5-10% range after costs for the enzymes.
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In order to ensure that the kibble quality is maintained, the following qualitative tests have been performed:
- palatability test and stool quality judgment
- starch gelatinization
- texture analysis
- storage stability at 30°C (86°F) and 80% relative humidity
- residual enzyme activity
The palatability test was carried out with 20 dogs for 4 days. In all cases the stool quality was judged as a 4, i.e. normal (1-5). Palatability (first choice and consumption ratio) was judged the same, i.e. no significant difference between samples treated with Novozymes amylase and untreated samples.
The starch gelatinization in kibbles treated with Novozymes amylase was not less than that in untreated kibbles; in fact, there was even a tendency to more complete starch gelatinization in the treated samples. The texture analysis did not show any significant difference between treated and untreated samples.
In the storage stability test, the kibbles did take up some water within the first week, but remained stable during the following 7 weeks. No apparent differences were observed between treated and untreated samples.
The residual enzyme activity measurements showed a residual activity of Extruzyme™ Pro and Extruzyme Plus in the range of 20-80%, the figure being highly dependent on actual extrusion conditions such as residence time and process temperature. Extruzyme Extra has no detectable residual enzyme activity under normal extrusion conditions.
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The range of Novozymes amylases suitable for this application as well as their selection parameters, i.e. residual enzyme activity in the final kibble and nature of the microorganism, are summarized below:
- Extruzyme Pro: Potentially a relatively high residual enzyme activity due to the heat stability of the enzyme. The enzyme is produced by GMOs.
- Extruzyme Plus: Potentially a relatively low residual enzyme activity due to lower heat stability of the enzyme. The enzyme is produced by non-GMOs.
- Extruzyme Extra: No detectable residual enzyme activity. The enzyme is produced by non-GMOs.
We recommend the following dosage ranges based on dry feed to the extruder:
- Extruzyme Pro............................0.10-0.20%
- Extruzyme Plus..........................0.025-0.05%
- Extruzyme Extra..........................0.03-0.06%
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The effect of using a Novozymes amylase in extrusion is very robust in respect of food formulation and starch content, provided the starch content is between 20 and 50%. In some cases, we have seen capacity increases of around 50% for cat kibbles with low starch content.
The enzymes must be applied in a liquid form and added with water during the preconditioning stage. They may also be added directly to the preconditioner, but in this case they should be diluted with at least 9 parts water to ensure proper distribution. The suggested set-up is shown in Figure 1 and Novozymes is in a position to recommend a dosage system.
As enzymes are heat-sensitive, it is important that the temperature is kept within 30-90°C (85-195°F) in the preconditioner and not above 150°C (300°F) at the end of the extruder.
It is important to relate the enzyme dosage to the feeding system, i.e. the RPM of the feed screw, which means that feed screw calibrations need to be performed. It is also obviously important to make sure that the surrounding system can deal with the increasing extruder capacity when the Novozymes amylases are added.
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When the Novozymes amylases degrade the gelatinized starch, the structure of the starch is to some extent weakened. The right dosage is therefore a balance between reducing viscosity and reducing the water-binding capacity of the starch.
An excessive enzyme dosage, e.g. twice that recommended above, will weaken the starch so much that the kibble will not be able to expand as much as usual. The kibble may even puncture when it leaves the die and the bulk density will increase significantly.
At the optimum dosage, i.e. the range listed above, the water-binding capacity of the starch will be reduced. At first glance, the kibble will appear sticky and wet. The solution to this is to reduce the water flow rate by approx. 10%, even when the feed rate is increased by 25%. This means that the moisture content in the kibble on leaving the extruder will go down. A reduction of 25% is often observed, meaning overall savings in the drying cost. The moisture level may be reduced from 28% to 21%.
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Ideally, the enzyme dosage system should be connected to the existing dosing system for the water, which enters the preconditioner immediately after the feed inlet. The enzyme line should be connected between the water flowmeter and the preconditioner. The enzyme dosage should be controlled by the flowmeter.
The enzyme flow at any given time should be regulated by the RPM of the feed screw. Thus, if the RPM of the feed screw changes, the enzyme feed should change correspondingly. If the metering pump controls the enzyme flow, the red loop is not necessary. If valve V1 controls the enzyme flow, then the red loop is necessary.
Further and detailed information with regard to the enzyme dosage system can be found in Enzyme dosing system for Amulases in extrusion.
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If the system is set up as in Figure 1, it is important to calibrate the feed screw so that the precise relationship between the feed screw RPM and the dry feed rate is known. The enzyme dosage is then calculated and the enzyme flowmeter calibrated, probably to between 0 and 250 ml/minute depending on the extruder capacity. It is important that the enzyme flowmeter is regulated and controlled by the feed screw so that the enzyme dosage is adjusted according to feed flow. This means that if the feed stops, the enzyme and water flow should stop immediately.
When the system is set up and ready to run, the following start-up procedure should be followed.
First run the extruder with the normal test food formula and at the optimized feed rate for at least 30 minutes to ensure that everything is running normally. Then open the enzyme valve and observe the power consumption indicated by the AMP meter. After a few minutes, the current requirement should go down by 15-25%. Then increase the RPM of the feed screw until the power consumption is similar to before addition of the enzyme. The feed RPM should usually be increased by at least the same magnitude as the decrease in current, i.e. an increase of 15-25% or more.
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Our experienced technical service staff are available worldwide to assist you with additional service and support, as well as assistance during start-up at your premises.
Novozymes is used to working closely with its partners and under conditions of full confidentiality, irrespective of whether any formal secrecy agreement has been concluded. However, if needed, Novozymes is prepared to enter into a formal secrecy agreement.
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