Physical and biochemical changes in feeds During processing

Materials used for feeding fish may be subjected to drying, freezing, grinding, radiation, hard pelleting and expansion pelleting. During these processes, physical and chemical changes occur due to inherent enzymes, contamination by microorganisms, oxygen, temperature, pressure and ionization of molecules. These changes are not reflected in the gross composition of the major nutrient classes (protein, fat, carbohydrate, ash), but in the intrinsic nutrients, organic additives and digestibility. Experimental work showed the hard pelleting process to be destructive to added enzymes.