258 FISHERY INDUSTRIAL PRODUCTS 



protein will be less, but the biological value of the protein present will 

 not be diminished. 



After meals are removed from the driers, the oil oxidizes and the meals 

 go through a period of heating spontaneously. If care is not taken, the 

 meals will heat to very high temperatures, high enough to char or ignite 

 them. Meals have a greater tendency to heat if they have a high oil con- 

 tent. Olafsson^^ found that for oil extracted from meal on the first day, 

 the lower the moisture content in the meal the higher is the peroxide 

 number of the oil. If meals are allowed to heat to high temperatures, 

 their nutritional value is affected, due at least partially to decreased 

 digestibility. 



The problem of spontaneous heating has been practically eliminated 

 in modern commercial operations. The meal is permitted to heat under 

 controlled conditions that keep the temperature low and the damage to 

 the nutritional quality of the meal at a minimum. 



The temperature of drying and the method of processing have long 

 been suspected as important reasons for variability in nutritional values 

 of fish meals. Conflicting reports about their importance have appeared 

 in the literature. High temperatures at the end of the drying period, when 

 the moisture content is low, will scorch the meal. A survey of commercial 

 menhaden meals'^ was made to determine their protein quality. The values 

 of 97 meals varied by more than 100 per cent in these tests in which the 

 fish meal was fed as the sole source of protein and the growth rate of 

 chicks was measured. Although two-thirds of the meals dried at high 

 temperatures were of good or intermediate nutritional value, one third 

 were of poor quality. In contrast, none of the meals dried at low tem- 

 peratures were of poor quality. Thus meals of good nutritional value can 

 be dried at high temperatures under some conditions. Although tempera- 

 tures of drying effect quality, other factors are also important. 



Fish Solubles 



The use of fish solubles in poultry diets was started about 1945'", after 

 a commercial process was developed to condense stickwater. These solu- 

 bles are sometimes added back to fish meal to produce 'Svhole" meal. Solu- 

 bles have also been spray-dried to make them easier to ship and handle, 

 but this is unsatisfactory because the dried solubles are hygroscopic. 



Solubles arc added to diets primarily for their nutritional value, al- 

 though they also have the advantage of reducing dust in mash feeds. They 

 are an important source of unknown growth factors, B vitamins, and trace 

 minerals. Although solubles do contain amino acids, they are not a good 

 source because the amounts are variable. 



