Processing and preparation of pet animal foods 

Processing technology includes equipment, standards, methods, and quality controls employed in the making of prepared pet foods. The quality of the ingredients selected is an important aspect of providing a high quality pet food . However, another equally important factor to take into consideration is the impact the processing technology has on the nutritional quality of the food.

Processing determines the shape, size and destiny of the prepared pet food, plus most importantly, it affects: 

• Digestibility

• Palatability

• Sterility

• Nutritional values

A Few critical areas of processing includes: 

• Cooking temperature, pressure, time

• Ingredients combinations and sequence

• Extruder speed

• Design of extruder, screw thread and die .

These can all have impact of these important factors.

Manufacture of dry pet foods

Every aspect  of  manufacturing process is designed to ensure a high quality nutritionally complete pet food is produced. This is how it is done.

1. The ingredients are selected from ingredient suppliers who must conform to certain industrial standards. Some ingredients are refined to ensure their maximum digestibility and nutritional value. In addition, the storage of the raw materials is strictly controlled to prevent any loss of any nutrient quality. Raw materials are used in strictly date order, so that none gets consistently ‘left behind’ at the bottom of the storage container. A just-in-time system is employed.

2. First dry raw materials e.g. corn and rice are drawn from soils and mixed with vitamins, minerals, and other micro-ingredients. The ratio of ingredients in the mixture is computer controlled.

3. Once combined, this mixture is then ground to specifications, and then stored until the rest of ingredients are ready to be added.

4. This ground mix is channeled into a machine called a Conditioner, at a constant speed, while the liquid ingredients, including the meat injection plus processing aids, (such as water ) are added to it. This stage is carefully monitored as any variation in the ratio of ingredients can have detrimental effects. The temperature of the mixture is between 70-80° C before entering the extruder and contains 25-30% moisture.

5. The mixture is fed quickly into a mixer through the extruder, with the use of rotating screw. As it goes through the mixer is subjected to high pressure (30-60 bar) and heat (120-130° C) for 20 seconds, which cooks it in a uniform fashion. It takes between 20 and 60 seconds for the raw ingredients to be transformed into the cooked and formed product once it enters the extruder.

6. As the mix exits the extruder it runs through a die, which shapes it. As the pressurized mix rapidly exits the die opening water vaporizes from the product, resulting in expansion of the cooked doughy mix, which provides the desired texture.

7. The mixture then meets a rotating blade, which cut it into the desired size.

8. The kibbles are then put into dryers and dehydrated from 25-30% moisture to less than 10% moisture.

9. The kibbles are then allowed to cool , before being sprayed with a coating of e.g. liquid fat or digest, to enhance digestibility and add protien and fat to the food.

10. The dry food is then ready for packaging. The label includes a code that indicates the time and location of manufacture, plus a use –by date is stamped on the package.

11. The packages then go through a metal detector, by way of a final check, to ensure no foreign objects have been enclosed.

12. The packages are stored in a computerized warehouse before being transported by vehicles that must meet a certain appropriate standard for the transport of food to retailers and distributors.

Extrusion technology

Screw extrusion is the cooking, shaping and cutting of raw ingredients into a specific kibble shape and size in a very short space of time ,while simultaneously destroying detrimental microorganisms effectively. Today Extruders contain a straight shaft; with threads of specific heights (similar to the threads of a screw) that rotates ,while enclosed in a stationery barrel. The rotating shaft drives the mixed ingredients through the stationery chamber with sufficient heat and pressure to extrude a cooked and formed product through a small exit hole . In extrusion technology, extruder speed, design or configuration of extruder screw segments, and type of screw threads and opening, can all have major impact on the product’s nutritional value. The components and functions of extruder technology include: 

• Feeder: Feeds dry ingredients into the conditioner.  

• Conditioner: Where dry and wet ingredients are mixed.

• Screw: Moves the food forward and helps increases the pressure in the extruder chamber.

• Extruder chamber: Encloses the screw and contains the food . this is where the mixture

  is mixed vigorously and undergoes heat friction that causes and increase in the

  temperature in the chamber up to 180° C.

• Steam lock: Enables more mixing and an increase in heat through providing resistance to

  the flow of the mixture.

• Feed zones: Feeds the mixed ingredients uniformly for the conditioner to the extruder.

• Transition zone: Where the mixture becomes vicious and doughy and the pressure

  increases.

• Matering zones: Where pressure increases further as the mixture is moved towards the

  narrow exit hole, sufficient to extrude or push the mixture through the die.

• Die: This is the exit hole. Specific designs and sizes of die determine the different sizes,

  shapes and textures of kibbles that are produced.

• Cutter: Cuts cooked mixture into uniform size.

Extrusion technology is advantageous over other dry food technologies for the following reasons: 

• It is more productive than other dry food manufacturing processing as it allows for the

  continual production of different sizes and shapes of kibble without delay in

  production.

• It is more energy efficient, as lower moisture during the cooking process means less

  heat energy is needed.

• It is more environmental friendly than other dry feed technologies, as it produces less

  effluents and contaminants. It requires only water and /or steam to make the food.

• Meat injection technology which increases palatability.

• The ability to produce foods containing large amounts of fresh meat.

• It is able to process larger variety of foods by enabling many more different

  combinations of ingredients than before.

• Better control, providing a consistent good quality product.

Comparing pet foods 

Types of pet foods: The three main types of pet foods are dry, soft-moist and canned products. These vary in a number of characteristics including moisture, cost, palatability and amount of nutrition delivered per pound of food. Evaluating a pet food diet  should include consideration of all these factors. Inspite of this variation, with today’s advanced technology, all types of pet food and products can be formulated  to provide complete and balanced nutrition for dogs. 

Dry diets: Most dry dog foods contain 18 to 27% protein, 7 to 15% fat, less than 12% moisture and 35 to 50% carbohydrate ( also expressed as nitrogen free extract ). These diets deliver between 1400 and 2000 metabolizable kilocalories per pound of product. It is generally accepted that dry pet foods are more economical to feed than the soft-moist and canned varieties and offer more convenience to pet owners. Dry products also have crunchy kibbles, which help reduce the build-up of  plague and tartar on the pet’s teeth . 

Soft-moist diets: Soft-moist dog foods contain approximately 16 to 25% protein, 5 to 10% fat, about 25 to 35% carbohydrates and 30% water( moisture levels sometimes go as high as 50%). High quality soft-moist diets contain approximately 1200 to 1350 metabolizable kilocalories per pound of product. Soft-moist dog foods generally offer higher palatability as compared to dry diets, are convenient to serve and store easily. They are more expensive to feed than dry diets.

Canned diets:  Canned pet foods contain between 8 and 15% protein in dog food products. This type of diets contain between 2 to 15% fat, depending on the type(s) of animal tissue used in diet. The moisture content for canned pet foods is approximately 75% (less than 78%) . 

Canned dog foods deliver 375 to 950 metabolizable kilocalories per pound. Total food consumption is high because of the low caloric content. The nutrient balance is dictated a great deal by the type of animal tissue used in the diet. These diets offer the highest palatability and the highest cost per serving when compared to the dry and soft-moist product. In addition, canned products are less convenient to serve than other product type. Once a can is opened, unused food should be stored in the refrigerator. 

Table 1. Comparison of pet food types 

All types of products may be complete and balanced depending on the formulation. To determine if this is the case, be certain the label states that the product is completely balanced for the life stage of the pet to which it is being fed. 

Dog food categories for young animals

Growth foods-Growth or All Life Stages Claim

      Protein                         21% or greater

      Fat                                8% fat or greater 

Adult foods-All life Stages Claim or Maintenance Claim 

           Protein                         21% or greater

      Fat                                8% fat or greater

Dog food categories for adult animals

Growth foods-Growth or All Life Stages Claim

(Approximately for reproduction and hardworking dogs )

            Protein                         21% or greater

      Fat                                8% fat or greater

Adult foods-All life Stages Claim or Maintenance Claim

      Protein                         21 – 26%

      Fat                                8 – 18%

Reduced calorie foods -  Maintenance Claim

          Protein                         14 – 25%  

      Fat                                7 –8% 

Performance foods - All life Stages Claim

           Protein                         27% or greater

           Fat                                9% or greater

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