The Impact of Feed Pelleting on Enzyme Thermostability
In animal feed manufacturing, the process of pelleting is used to convert mash feed into compressed pellets. Pelleting provides several advantages, such as ease of handling, reduction of dust and waste and standard composition. The use of pelleted feed is also known to improve the feed conversion ratio (FCR) due to better digestibility and absorption of nutrients by the animal. During the conditioning phase of pelleting, the feed is subjected to steam, which helps reduce or eliminate pathogens such as Salmonella that could be present in the feed.
Conditioning time can vary from a few seconds up to several minutes depending on the type and formulation of the feed. The temperature during conditioning typically ranges from 70°C to 100°C. After conditioning, the feed is extruded through a pelleting die, which for a short time raises the temperature of the feed incrementally due to friction. Because enzymes are proteins, they are susceptible to being denatured by heat and pressure. Denaturing essentially alters the structure of the enzyme, resulting in decreased activity levels and decreased efficacy of the enzyme.
Ways to Improve Enzyme Thermostability
Maintaining an acceptable level of enzyme activity post-pelleting can be challenging. To improve thermo-tolerance, multiple solutions have been developed.
- Post-pellet liquid application can be used to protect the enzyme from denaturation caused by heat treatment. This solution is relatively complex and expensive because it requires the purchase and installation of specialized equipment, space in which to store the liquid enzyme and careful calculation of the amount of enzyme to apply.
- Application of a protective coating to the enzyme before pelleting is another alternative that can protect the enzyme from exposure to high levels of heat and moisture during feed manufacturing. This approach may reduce the efficacy of the enzyme because the coating may not fully dissolve in the upper digestive tract of the animal. It is difficult to achieve a coating design that can withstand the high heat and moisture content of the pelleting process, but subsequently, dissolve in the lower temperature and higher moisture conditions of the animal’s gut.
- Intrinsically thermostable enzymes are considered by many enzyme manufacturers to be the optimum solution. These enzymes are developed from thermophilic and hyper-thermophilic organisms and are known to have unique structure and function properties of high thermostability at temperatures above 85°C. Intrinsically thermostable enzymes can be added to animal feed without special coating and still retain high activity levels post-pelleting.
Intrinsically thermostable enzymes are often a preferred option for both feed mills and animal producers because they are available in dry form. Dry-form enzymes work well with standard equipment as they can be hand-added in a premix to pre-pelleted feed or can be used with a micro-ingredient system. Enzymes in dry form have a longer shelf life than those in liquid form and can be easily transported, distributed, stored and handled. Most importantly, the activity level of intrinsically thermostable enzymes is not lost due to high conditioning and pelleting temperatures.
Blog post originally published in BioResource International website (http://briworldwide.com).
Amerah, A. M., C. Gilbert, P. H. Simmins, and V. Ravindran. 2011. Influence of feed processing on the efficacy of exogenous enzymes in broiler diets. World’s Poultry Science Journal 67: 29 – 46.
Ravindran, V., and J-H Son. 2011. Feed enzyme technology: Present status and future developments. Recent Patents on Food, Nutrition & Agriculture 3: 102-109.
Vieille, C., and G. J. Zeikus. 2001. Hyperthermophilic enzymes: sources, uses, and molecular mechanisms for thermostability. Microbiology and Molecular Biology Reviews 65: 1–43.