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pstinard · 05-07-2015, 10:39 AM

Effect of cooking on quality and digestibility of nutrients

Proponents of feeding raw food diets suggest that cooking decreases the nutritional value of meats by decreasing protein digestibility and by destroying enzymes naturally present in foods.

Natural enzymes present in ingredients are proteins and thus cooking temperatures will indeed change their physical properties and deactivate them. However, enzymes in food add very little, if any, value to the digestion processes of dogs and cats. Enzymes in meat and other food ingredients are not specialized digestive enzymes and will not participate in the digestion or assimilation of proteins. Some raw foods contain enzymes that actually serve to inhibit digestion or destroy essential nutrients, such as avidin in raw eggs, thiaminase in fish, and trypsin inhibitory factors in various raw foods. In this case, cooking greatly enhances the nutritional value of the ingredients.30 and 31

Grains and other plant-based ingredients benefit significantly from cooking. Cooking increased the digestibility of the starch from grains between 14% and 208% in multiple studies.32 Although overcooking can decrease protein digestibility, proper cooking can increase the digestibility of protein from both animal and vegetable sources.30, 31, 32, 33 and 34 This is thought to occur due to the physical restructuring or unfolding of proteins during the cooking process, providing more binding sites and making them more susceptible to digestive enzymes and reducing the energy required for digestion.32 and 34 Gentle cooking in a microwave did not compromise the digestibility of a raw feline diet and may provide a way to sterilize raw food diets for pets.35

About Extrusion Cooking

The effects of cooking on nutrient quality and digestibility can vary with type of cooking method, temperature, time, and amount of moisture.30, 34, 36 and 37 The vast majority of dry foods are cooked using an extrusion process. Extrusion uses a combination of moisture (25%–35%), temperature (100°–150°C), pressure (20–30 bars), and mechanical shear (0.5–5 minutes) to quickly cook the product.38 Correct extrusion conditions favor higher retention of amino acids, high protein and starch digestibility, decreased lipid oxidation, and higher retention of vitamins.36 In addition, the extrusion process denatures undesirable enzymes such as antinutritional factors (trypsin inhibitors, haemagglutinins, tannins, and phytates) and sterilizes the finished product.36 Although overcooking using any method, including extrusion, can decrease the nutritional quality of foods, the relatively high moisture content, moderate temperatures, and short cooking duration help to maintain the nutritional quality of extruded foods.38

Additives and preservatives

Pet owners may be concerned about the list of chemical-sounding names in the ingredient list of pet foods or may have read about “unnecessary additives or preservatives”. For these clients, it will be important to help them understand the meaning and use of the “chemicals”. It may help to observe a quote from Dr Nathan Myhrvold, shared during televised interview on PBS: “Lots of folks think of this as, ‘Oh, my god, there's chemicals in my food!’ Well, I'm here to tell you that food is made of chemicals; those chemicals are made of elements; and that's the way it is here on planet Earth. Everything actually is a chemical.”39
Many of the ingredients listed on pet food labels are vitamins and minerals. Pet owners may not recognize “pyridoxine hydrochloride” as Vitamin B6, “menadione sodium bisulfite complex” as Vitamin K, or “copper proteinate” as a source of essential dietary copper, for example. These are among the 40+ essential nutrients that dogs and cats require and are critical to assure a nutritionally complete and balanced diet.

Other additives may include natural (eg, mixed tocopherols or vitamin E) or synthetic (eg, BHA, TBHQ, ethoxyquin) antioxidant preservatives that function to keep dietary fats and other nutrients stable during storage. Without these antioxidants, the essential fatty acids could become oxidized or rancid and their nutritional value destroyed. Concerns have been raised about the use of chemical or synthetic antioxidants, suggesting that they can be toxic or carcinogenic. Toxicity, for all compounds, is related to dose as well as to route in exposure. For BHA and butylated hydroxytoluene, for example, an extremely high dose can induce adverse effects but the data show they are safe and even suggest they may be anticarcinogenic at lower levels of use.40, 41 and 42 As used in pet foods, these antioxidants are safe and are critical to maintain the nutritional value of foods.

05-07-2015, 10:39 AM	#6
pstinard YT 3000 Club Member Join Date: Apr 2013 Location: Urbana, IL USA Posts: 3,648	Effect of cooking on quality and digestibility of nutrients Proponents of feeding raw food diets suggest that cooking decreases the nutritional value of meats by decreasing protein digestibility and by destroying enzymes naturally present in foods. Natural enzymes present in ingredients are proteins and thus cooking temperatures will indeed change their physical properties and deactivate them. However, enzymes in food add very little, if any, value to the digestion processes of dogs and cats. Enzymes in meat and other food ingredients are not specialized digestive enzymes and will not participate in the digestion or assimilation of proteins. Some raw foods contain enzymes that actually serve to inhibit digestion or destroy essential nutrients, such as avidin in raw eggs, thiaminase in fish, and trypsin inhibitory factors in various raw foods. In this case, cooking greatly enhances the nutritional value of the ingredients.30 and 31 Grains and other plant-based ingredients benefit significantly from cooking. Cooking increased the digestibility of the starch from grains between 14% and 208% in multiple studies.32 Although overcooking can decrease protein digestibility, proper cooking can increase the digestibility of protein from both animal and vegetable sources.30, 31, 32, 33 and 34 This is thought to occur due to the physical restructuring or unfolding of proteins during the cooking process, providing more binding sites and making them more susceptible to digestive enzymes and reducing the energy required for digestion.32 and 34 Gentle cooking in a microwave did not compromise the digestibility of a raw feline diet and may provide a way to sterilize raw food diets for pets.35 About Extrusion Cooking The effects of cooking on nutrient quality and digestibility can vary with type of cooking method, temperature, time, and amount of moisture.30, 34, 36 and 37 The vast majority of dry foods are cooked using an extrusion process. Extrusion uses a combination of moisture (25%–35%), temperature (100°–150°C), pressure (20–30 bars), and mechanical shear (0.5–5 minutes) to quickly cook the product.38 Correct extrusion conditions favor higher retention of amino acids, high protein and starch digestibility, decreased lipid oxidation, and higher retention of vitamins.36 In addition, the extrusion process denatures undesirable enzymes such as antinutritional factors (trypsin inhibitors, haemagglutinins, tannins, and phytates) and sterilizes the finished product.36 Although overcooking using any method, including extrusion, can decrease the nutritional quality of foods, the relatively high moisture content, moderate temperatures, and short cooking duration help to maintain the nutritional quality of extruded foods.38 Additives and preservatives Pet owners may be concerned about the list of chemical-sounding names in the ingredient list of pet foods or may have read about “unnecessary additives or preservatives”. For these clients, it will be important to help them understand the meaning and use of the “chemicals”. It may help to observe a quote from Dr Nathan Myhrvold, shared during televised interview on PBS: “Lots of folks think of this as, ‘Oh, my god, there's chemicals in my food!’ Well, I'm here to tell you that food is made of chemicals; those chemicals are made of elements; and that's the way it is here on planet Earth. Everything actually is a chemical.”39 Many of the ingredients listed on pet food labels are vitamins and minerals. Pet owners may not recognize “pyridoxine hydrochloride” as Vitamin B6, “menadione sodium bisulfite complex” as Vitamin K, or “copper proteinate” as a source of essential dietary copper, for example. These are among the 40+ essential nutrients that dogs and cats require and are critical to assure a nutritionally complete and balanced diet. Other additives may include natural (eg, mixed tocopherols or vitamin E) or synthetic (eg, BHA, TBHQ, ethoxyquin) antioxidant preservatives that function to keep dietary fats and other nutrients stable during storage. Without these antioxidants, the essential fatty acids could become oxidized or rancid and their nutritional value destroyed. Concerns have been raised about the use of chemical or synthetic antioxidants, suggesting that they can be toxic or carcinogenic. Toxicity, for all compounds, is related to dose as well as to route in exposure. For BHA and butylated hydroxytoluene, for example, an extremely high dose can induce adverse effects but the data show they are safe and even suggest they may be anticarcinogenic at lower levels of use.40, 41 and 42 As used in pet foods, these antioxidants are safe and are critical to maintain the nutritional value of foods.