of enzymes to partially solubilize the cake pro- 

 duced by the pressing of fatty fish. A totally 

 soluble FPC from press cake would probably 

 not be feasible because the native fish enzymes 

 are inactivated in the initial cooking step. An 

 uneconomical level of commercial enzyme would 

 be required to obtain a good yield of soluble 

 product with an adequate amino acid profile. 



Feed to digesters. — A process outline based 

 on press cake is shown in Figure 15. The press 

 cake feed is prepared by the standard wet re- 

 duction process of the fish meal industry. The 

 whole fish are cooked and then pressed in a con- 

 tinuous screw press. The press liquor is screened 

 to remove suspended solid "foots" and then fed 

 from a hold tank to a centrifuge where the crude 

 fish oil is removed. The oil is clarified by a hot 

 water wash and a second centrifugation before 

 it is pumped to oil storage. The stickwater from 

 the first centrifugation is fed to the digesters 

 and mixed with the press cake to form the slurry 

 for hydrolysis. The system of evaporators used 

 in a fish meal plant to jirepare concentrated sol- 

 ubles from stickwater is not required. 



Enzymatic hydrolysis — A product with PER 

 equal to that of casein has been prepared using 

 the alkaline protease, Alcalase, at a level of 0.1 lb. 

 per 100 lb. of alewife press cake. Bromelin or 

 ficin might be more suitable since no pH adjusts 

 ment would be required. After a 3-4 hr hydrol- 

 ysis at 55°-60°C, the bones are separated from 

 the hydrolysate on passage through a vibrating 

 screen. 



Processing — Additional oil may be removed 

 from the hydrolysate by centrifugation, but ex- 

 perimental results thus far indicate that the de- 

 gree of oil removal possible by this means does 

 not justify the inclusion of a centrifuge at this 

 stage of the process. The lipid content of the 

 FPC would then depend on the efficiency of the 

 pressing operation. Based on nornial fish meal 

 operations a level of 6 to lO'^r residual lipids on 

 a dry weight basis would be expected. This level 

 could be reduced by hot water washing of the 

 press cake prior to hydrolysis. If most of the 

 solids could be recovered by screening, the wash 

 water would be mixed with the press liquor 

 for centrifugation. After oil separation the 



FISH 

 UNLOADING 



WEIGHING 

 CONVEYOR 



WATER DUMP 

 TANK 



STOmE - N "°"'' H ""^ 

 I _ iJJ s » ♦ * t I ISO. 16 



SCREEN 



HOLD 

 TANK 



OIL 

 CENTRIFUGE 



CHILLER 



SALT 

 STORAGE 



BRINE 

 MAKE UP 



SEA 

 WATER' 



SEA WATER 

 PUMPS 



190.101 



190 91 



FEEDER 



5 



i'l "1 WHIfR I SlUOCE 



HOLD 

 TANK 



OIL 

 CENTRIFUGE 



FISH OIL 

 STORAGE 



DIGESTOR 



Al 



Itllmi 190.121 

 INTIOXIOmil [90.19 

 Ca|0«)2 190. IS] 

 N30H 190.111 



SW 



SCRUBBER 



TaF)-*' EXHAUST 



|9l.2i 



SCREEN 



CONVEYOR 



Figure 1 5. — Suggested process outline for production of an FPC from fatty fish press cake by enzymatic hydrolysi: 



25 



