How does the process of extrusion affect the feed for our dogs
While thermal processing (extrusion) pet food offers a number of benefits, extensive processing can increase the variability, destroy essential nutrients and create bad products.
Thermal processing, also known as cooking or extruded pet food, offers a number of benefits, including convenience, better taste and texture, consistency, improved pathogen control whilst also reducing spoilage. However, extensive processing can destroy essential nutrients and create an unhealthy reaction through its byproducts. From the perspective of a food formulator, this creates a dilemma on how to ensure that the product is sufficiently fortified avoiding excessive addition of nutrients.
Given that we have been sharing food with dogs and cats since the dawn of civilization some 15,000 years ago, one would think that we would have dealt with most of the food issues, however, compared with human food, we only have limited information about how the process effects nutrition and viability of pet food.
Why is this important? By some estimates, more than 300 million dogs and cats around the world rely completely on commercial diets for their livelihood. For most pets, this means that they eat food that has been extruded. Given that many of the necessary nutrients are destroyed under thermal pressure, also taking into consideration moisture conditions common in cooking, we must be aware that their contents after processing may not ensure an adequate supply of nutrients and vitamins.
These factors have been a problem in our recent past, for example, looking at the causes of nutrition-based diseases, such as dilated cardiomyopathy in dogs and thiamine deficiency in cats. To do a better job of consistently providing for our pets, we need to gain a better understanding of the influences these processes have. This allows us to convert the "art of fortification" into more than a science. We have only fragments of information about how the process effects nutrition and viability of pet food.
In the pet food industry unlike that of humans, many of the raw ingredients used in commercial pet foods have been extensively processed (eg, meat and bone meal, tallow, rice bran, etc.), the ingredients in the feed are mixed together and then processed under harsh conditions (eg, extrusion) and the final product is expected to be shelf-stable for over one year at ambient temperatures.
In human food usually only a portion of the ingredients or components of the diet are processed, we eat several meals during the day and most of these are refrigerated, frozen or consumed within a few weeks of production. Livestock feeds use a similar approach to that of pets, but they are rarely subjected to heat treatment and are often provided as food the same day that they were produced, so shelf life is of little interest. These differences have profound implications on the nutritional value of the final product.
Along with feed ingredients, the most important challenge in processing is the result of the rendering process. This is important because protein meals are found in almost all dry pet food. These protein meals such as meat byproducts, bone and chicken flour, have been under intense rendering to reduce moisture and fat. While the intent of the process is to stabilize and homogenize the resulting material, significant variability exists nutritionally. The nutrients most affected by the process are essential amino acids such as lysine and sulfur, amino acids, methionine and cysteine.
Lysine loss from these protein meals due to a non-enzymatic reaction is well known, there is a decrease of a lesser extent in the región of 50 to 60% with methionine and cysteine. The rendering process also affects the viability of fats due to oxidation. If left without preservatives the oils remaining in protein meals can start to oxidize after a few days, resulting in the formation of peroxide and, ultimately, the destruction of essential fatty acids such as linoleic acid.
According to a study by Murray in 2001, over-cooked starch can increase fiber digestion. There his effect can alter the use of the fiber, changing the ratio of soluble fiber to insoluble fiber thus negatively effecting the specific contribution to total dietary fiber.
Thus, after many studies it can be said that the extrusion process itself may actually improve availability of amino acids such as lysine.
All vitamins seem to be effected to some degree in every step of the process from production to storage. The loss of fat soluble vitamins (A, D, E, K) are the most significant in extruded products, with rates of over 50% loss before packaging. With wet food vitamin B and water soluble thiamin soluble can be almost entirely lost due to their reaction with heat, moisture, sulfites, and high pH tiaminasa enzymes found in fish and meat organs.
This is not an exhaustive list, and many of the effects of heat treatment have not yet been described. From the information so far, it seems relatively obvious that this treatment has some significant effects on pet nutrition. Whilst some of the processes conditions are nutritionally beneficial for the animals, in several areas, nutritional fortification must compensate for significant losses during these processes. The three most significant groups in order of importance are vitamins, followed by, often overlooked, sulfur amino acids and finally essential fatty acids.
In these several areas, nutritional fortification must compensate for the significant losses due to extrusion.
Nowadays, we support the nutricional ideal of super-fortification before extrusion and the nutrient analysis after extrusion. Overall, this has proven to be effective, but there are occasional toxicities and deficiencies that can result in nutricional deficits. This would suggest a more comprehensive assessment of the nutritional effects of thermal processing of food for pets with the best models to support nutritional fortification.
SOURCE: http://www.petfoodindustry.com
By Greg Aldrich, PhD
