FISHERY INDUSTRIES OF THE UNITED STATES, 1935 83 



to conduct a series of cooperative bacteriological studies at the food 

 products laboratory of the Massachusetts State College, Amherst, 



Mass. 



STUDIES DEALING WITH THE SPOILAGE OF FISH 



Studies dealing with the spoilage of fish were continued, attempting 

 to correlate chemical tests with the condition of the fish. Work was 

 limited to two species, the cod and the mackerel. The former is 

 representative of the nonoily fish and its spoilage proceeds in an 

 entirely different manner than do such oily fish as mackerel. It was 

 found that the ammonia content of cod increased fairly regularly with 

 spoilage, and by determining the amount of ammonia present, a 

 valuable auxiliary test for the freshness of cod was available to be 

 used with the electrometric method described in previous reports, as 

 applicable to haddock. It was found that a determination of free 

 amino acids in cod, during spoilage while packed in ice, was of very 

 little value in determining the relative freshness. This is due to the 

 fact that amino acids break down into intermediate spoilage products, 

 which are later decomposed. It was found that there was a small 

 initial rise in free amino acid content followed by a slow decrease. 

 Hydrogen sulfide determinations were also found to be of limited 

 value as a test of freshness in cod. In a few cases, significant amounts 

 of hydrogen sulfide were formed, but as a rule, the amounts were 

 almost negligible. 



In the case of mackerel, it was found that a determination of the 

 hydrogen sulfide content of the flesh was frequently a good index of 

 the degree of spoilage present. Mackerel frequently feed upon a 

 variety of minute shellfish known to the fishermen, because of the 

 peculiar orange-red color, as "red feed." It was found that fish 

 which had consumed large quantities of the "red feed" upon decom- 

 position gave off considerable quantities of hydrogen sulfide. In 

 some cases, 24 hours after having been caught, appreciable amounts 

 of hydrogen sulfide were found in the flesh of such fish. 



In the case of mackerel, the deterioration of the oil must be taken 

 into account. In order to be able to follow the changes occurring 

 in this oil without interference of the protein of the flesh, the oil was 

 extracted from the mackerel and stored under different conditions 

 of temperature and surroundings. It was found that a determina- 

 tion of the peroxide value of the oil could be correlated with the degree 

 of rancidity present if the storage temperature was less than about 

 65° C. At higher storage temperatures, this method is not applicable. 

 A determination of the free fatty acid content of the oil is in some 

 cases of some value but this test is far less sensitive than the peroxide 

 test. It was found that oil samples stored in a vacuum showed no 

 evidence of deterioration after 1 year's storage. \^'Tien stored in the 

 presence of carbon dioxide, the rate of oxidation of the oil was retarded. 

 It was found that maleic acid, which is sometimes used for retarding 

 decomposition of oils, had no effect when applied to mackerel oil, 

 but hydroquinone greatly decreased the rate of oxidation of mackerel 

 oil. Enzymes tend to facilitate the oxidation of the oil and, therefore, 

 a preliminary treatment to destroy enzymes decreased the rate of 

 oxidation of the oil, especially at low storage temperatures, but oxida- 

 tion still proceeded at an appreciable rate. 



