The development of blue discoloration in var- 

 ious fishery products has been reviewed many 

 times, most recently by Waters (1970). The 

 cause (s) have been only suggested and have 

 never been positively identified. The presence 

 of copper ions has usually been implicated in 

 the appearance of the blue color. Ammonia, 

 sulfur, ferrous, and ferric ions have also 

 been suggested as causes. Since ammonia 

 appears to be involved, freshness of the meat 

 is all important. Corrosion of the can's 

 seams may supply the Fe++ and Fe+++ ions 

 involved in blue discoloration, as the literature 

 suggests. 



The remedial treatments proposed are mainly 

 organic acids such as ascorbic, lactic, and citric. 

 Citric acid is widely used in the shrimp and 

 crab processing industry to inhibit certain na- 

 turally occurring enzymes and sequester trace 

 minerals which can act as pro-oxidant catalysts. 

 The purpose of this paper is to ( 1 ) report on 

 our efforts to determine the cause of blue dis- 

 coloration in canned blue crab meat and (2) 

 recommend an approved food additive that will 

 eliminate blue discoloration in canned crab 

 meat. 



I. DETERMINING THE CAUSE OF 

 BLUE DISCOLORATION 



A. Dead or Decaying Crab Hypothesis 



If a production manager is asked what is 

 causing the blue discoloration in his canned 

 crab meat he will probably say his supplier is 

 picking some dead crabs. It is true that meat 

 from crabs that had expired prior to processing 

 is darker and the texture is somewhat dif- 

 ferent. In fact, in the debacking process the 

 employee is asked to discard a crab suspected 

 of being dead using these criteria for rejection. 

 The "dead crab theory" of the processors was 

 only a hypothesis and was not based on ex- 

 perimental facts. The idea, however, seemed 

 to have merit, particularly in that both ammo- 

 nia and pH have been thought to play a part 

 in the blueing phenomenon. The ammonia 

 would be formed as a product of the breakdown 

 of proteins and the pH of the crab meat would 

 be raised. 



The following experiment was designed to 



test this theory: 



1. Processing dead crabs. — One hundred 

 lb of very active crabs were selected for this 

 study. They were randomly divided into two 

 lots. One of the lots was processed without 

 further treatment. The method we used con- 

 sisted of removing the meat from the boiled 

 crabs, placing the meat in 307 X 113 C-enamel 

 cans, and adding about 100 ml of brine. The 

 cans were closed under a 10- to 15-inch vacuum 

 and heat processed for 45 min at 240° F. This 

 method is a laboratory reproduction of an often 

 used commercial procedure. 



The second lot was exposed to the sun (75- 

 95° F) for 24 hr without the aid of a cooling 

 water spray or any other cooling eff'ect. We 

 hoped that this unusual treatment would cause 

 the crabs to die. After 24 hr exposui^e to the 

 sun, the crabs were examined to determine 

 their condition. Only 40 ;f of the crabs had 

 actually died but the remainder were somewhat 

 less than active. The lot was processed using 

 the commercial method described above. 



Representative cans from both lots were ex- 

 amined after 1, 2, and 4 days of storage. There 

 was no detectable discoloration of the crab 

 meat. Generally, when blueing appears in 

 canned crab meat, it occurs within 24 hr after 

 processing. After studying the results of this 

 experiment, we thought that perhaps the crabs 

 had not been dead long enough for degradation 

 products to be present. Consequently, we con- 

 ducted another experiment. 



2. Discarded crabs from debacking line. 



— Fresh crab meat was obtained from the pro- 

 cessing line of a commercial crab meat plant. 

 This lot was processed by our usual method 

 and served as the control. Discarded crabs 

 that were found dead prior to boiling were ob- 

 tained from the debacking line. The dead crabs 

 were from the same lot of crabs. The color 

 of the meat removed from the carcass was a 

 light grey and entirely different in color from 

 the meat picked from fresh, live crabs. This 

 meat was also processed in the usual manner. 

 The processed samples were stored and exam- 

 ined as above. 



The results showed that heat processing did 

 not cause any added discoloration over that 



