Strength and Durability of Feed Pellets Influenced by Different Particle Size Distribution, Pellet Volume and Dehydration Techniques

This article describes the effect of particle size distribution, pellet size and dehydration techniques on the improvement of physical properties of the pelleted feed products. It is shown that dehydration with vacuum has positive effect on durability when compared to air technique. Products volume and particle size distribution also had an effect on physical properties. INTRODUCTION In porous feed solids, an internal mass transfer may occur through the solid part or within the void spaces1. The dehydration techniques (DT) used on feed solids differs by their heat transfer properties. Moisturecontaining solids can be dehydrated by subjecting them to reduced pressures, better known as the vacuum. Vacuum DT (VDT) can be defined as an act to reduce the density of a gas in a vessel to a value adequate for its planned purpose. The first known vacuum dehydration of a commercial product was performed in 1948 for reducing field heat of lettuce2. All recent research advances have confirmed that vacuum technique is a method to shorten processing time and improve product quality3,4,5. Factors affecting the speed and efficiency of the product being dehydrated might influence the product quality also. These factors are: the surface area exposed to the atmosphere5, specific heat of the product prior the dehydration6, density7,8, porosity4,9,10 and particle size of the product8. Different moisture removal rates observed between conventional air DT (ADT) and VDT are caused by differences in the dehydration mechanisms11. ADT is achieved by heat transfer, while VDT by mass transfer. VDT is caused by pressure difference between the saturation pressure on the walls of the micro pore and flow of water vapor through the pore spaces to the surface of the moist-solids and surrounding atmosphere12. In VDT the porous structure plays an important role in determination of water flow3 during dehydration. The steam and the water are the important ingredients for manufacturing the feed product. One of the reasons is the given hydrogen bonds which are connecting various particles of mixed ingredients with the help of an adhesion process13. Water state and its type, bonded or free water, play an important role in these processes14. Close contact between the wetting adhesive molecules and the solid surface of the feed particles give rise to Strength and Durability of Feed Pellets Influenced by Different Particle Size Distribution, Pellet Volume and Dehydration Techniques Dejan Miladinovic1, Mette Sørensen2, and Birger Svihus3 1 Centre for Feed Technology FôrTek, Animal Experimental Centre, Norwegian University of Life Sciences, Ås, Norway 2 Nofima – The food research institute, Ås, Norway 3 Department for Animal and Aquacultural Sciences, Norwegian University of Life Science, Ås, Norway