222 U. S&S. BUREAU OF FISHERIES 
DEVELOPMENT OF TESTS FOR DETERMINING THE QUALITY OF FISH 
During recent years there has been evidenced a need for the develop- 
ment of chemical and bacteriological tests as contrasted to organo- 
leptic tests for determining the quality of fish. This has been occa- 
sioned by the desire of the fishery industry for control of quality at all 
stages in the production and marketing processes, so that the consumer 
may purchase a product of uniformly high quality. Moreover, there 
is a need for the industry to meet the requirements of thenew food 
and drug regulations. Such tests also would be needed in an inspec- 
tion and grading service for the fishery industry, such as has been 
under consideration in Congress during the past year, if the products 
handled and marketed are to be judged for quality on an impartial 
basis. In order to solve these problems, the Bureau during past 
years has conducted, and is continuing to conduct, considerable 
technological research on practical tests for quality which can be 
applied under commercial conditions. Mention has been previously 
made in this report of such tests for the quality of fresh crab meat 
and shucked fresh oysters. Following is a brief summary of the 
past year’s progress in developing tests which properly identify the 
quality of fish under various types of preservation and having varying 
initial degrees of freshness. 
FORMATION OF LACTIC ACID AND ACTION OF ENZYMES AS INDICES OF RELATIVE 
FRESHNESS OF FROZEN FISH 
One of the principal indications of strictly fresh fish is the stiffness 
of the muscle tissue due to rigor mortis. This condition is accom- 
panied by the development of a high lactic acid content in the flesh 
of the fish. The development of lactic acid progresses to a maximum 
in a period varying from 24 to 36 hours, then gradually diminishes. 
until it has completely disappeared. This study was imaugurated 
for the purpose of observing whether there was a correlation between 
the lactic acid content of fish flesh and the relative freshness of the 
fish during periods of storage after freezing. If it can be established 
that there is a correlation between relative freshness and amount of 
lactic acid present, it will be possible to make use of this determination 
for the grading of fish as to quality. Early in the course of this study 
it was found that it would be necessary to divide the problem into 
three phases: First, a study of the development and gradual disap- 
pearance of lactic acid in the fish flesh; second, the effect of enzymes 
produced by bacteria which utilizes the flesh of the fish as a medium 
for growth; and third, the effect of the action of autolytic proteolytic 
enzymes contained in the fiesh of the fish. 
Lactic acid.—Information obtained thus far on this phase of the 
study indicates that the lactic acid content of the flesh of sea trout 
and striped bass was 0.60 percent at death, or in rigor mortis, and 
about 0.40 percent after 50 days in cold storage. Flesh of these fish 
kept on ice for 3 days showed a lactic acid content of about 0.40 
percent, which decreased after 50 days in cold storage to 0.35 percent. 
The lactic acid content of the same kind of fish flesh kept without 
ice for 3 days dropped to 0.12 percent and showed no further change 
during 50 days in cold storage. It seems likely, therefore, that this. 
reaction may be used as a test for judging the quality of fish, especially 
when frozen. 
