KOURV. SPINELLI, and WIEG: PROTEIN AUTOLYSIS RATES 



TEMPERATURE 

 30°C 



TEMPERATURE 

 40°C 



TEMPERATURE 



sec 



200 



TEMPERATURE 

 60°C 



10 20 30 40 

 TIME (MIN) 



TEMPERATURE 

 70°C 



20 30 40 

 TIME (MIN) 



TEMPERATURE 

 80°C 



20 30 40 

 TIME (MIN) 



Figure 5. — Protein autolysis rates of eviscerated hake (inside) homogenates held at various pH's and temperatures. 



times) with azeotropic IP A at a ratio of 2 parts 

 IPA to 1 part fish. The first extraction was 

 carried out at ambient temperature, and the 

 final three extractions were carried aut at 70° C. 

 Yields were calculated after drying the fish 

 solids for 16 hr at 70° C at 25 inches of vacuum. 



RESULTS AND DISCUSSION 



The effect of autol.\i;ic activity on the sub- 

 sequent yield of FPC is shown in Figure 6. It 

 can be seen that while the acidified samples 

 showed the greatest loss of yield with time of 

 autolysis, the largest yield losses occurred dur- 

 ing the first 20 min. The pH values, time, and 

 temperature were arbitrarily chosen to simply 

 demonstrate the effect of autolysis with respect 

 to yield. They do, however, show a close cor- 

 relation with the autolysis data shown in the 

 previous experiment. For example, in refer- 

 ring to Figures 1 through 5, it can be seen 

 that the rate of NPN formation is greatest dur- 

 ing the first 20 min regardless of pH and tem- 

 perature. Several investigators (Whaley, 1966; 

 Sen, Sayanarayana Rao, Kadkol, Krishnaswamy, 

 Venkata Rao, and Lahiry, 1969) have proposed 

 acidifying comminuted fish prior to processing 

 without taking into account the effect of protein 

 losses due to autolysis. The combined exper- 



iments presented here clearly demonstrate the 

 need to control temperature and pH, both before 

 and during processing. 



SUMMARY AND CONCLUSIONS 



The above study shows that the endogenous 

 proteolytic enzymes in fish hydrolyze the pro- 

 teins into subunits that are not coagulable by 



Figure 6. — Effect of protein autolysis on the yield of 

 PFC made from inside hake. Autolysis was allowed 

 to proceed for 0, 20, 40, and 60 min at 50° C prior to 

 preparation of FPC. 



245 



