Table 1. — Results of adding chemicals to canned crab 

 meat to determine the responsible agent involved in 

 blue discoloration. 



Additive 



Concentration 



Visual 

 rating' 



NH4OH 



Fe(NH4)2 (804)2 



CuCl 



Cu(N03)2 



+ 

 + 







++++ 

 ++++ 



+ 

 + 







+ 

 + 

 + 



Distilled water 

 (control) . . . . 



' = no visible blueing 

 + == very slight blueing 

 -H- = slight blueing 

 +++ = moderate blueing 

 ++++ = heavy blueing 



A second experiment was designed to include 

 different compounds containing Fe++ and/or 

 Fe+++, NH+, and SO4 = ions alone. 



Dilute solutions of the following chemicals 

 were added to cans of crab meat as before: 

 ferrous ammonium sulfate [Fe(NH4)2(SOi)2], 

 ferric chloride [FeCls 6H2O], ammonium ci- 

 trate .[(NH4)2HC6H.507], ammonium nitrate 

 [NH4NO3], ammonium chloride [NH4CI], 

 ammonium sulfate [(NH4)2S04], cuprous 

 chloride [CuCl], cupric sulfate [CU2SO4], and 

 ammonium oxalate [(NH4)2C204 H2O]. Dis- 

 tilled water served as the control. After pro- 

 cessing and 3 days of storage, cans of each 

 variable were examined. Results are shown 

 in Table 2. 



The copper compounds were included again 

 to positively determine if copper could be in- 

 criminated in the blueing reaction. The results 

 show that every lot containing Fe++ and Fe+++ 

 ions had considerable blueing. Each Fe++ and 

 Fe-H-t- compound displayed about the same 

 degree of blueing when added at the same 

 concentration. Compounds (exclusive of 

 Fe(NH4)2(S04)2) containing either S04=, 

 NH4+, Cu+, or Cu++ ions did not discolor 

 the crab meat appreciably. Several addi- 

 tional experiments were conducted adding 



Table 2. — Results of adding chemicals containing S04=, 

 NH4+, Cu, and Pe++ and Fe+++ ions to canned crab 

 meat. 



Additive 



Concentration 



Visual 

 rating' 



CU2SO4 0.1 M 



CuCl 



(NH4)2C204 ■ HoO 



Fe(NH4)2(S04)2 



FeClg 6H2O 



(NH4)2HC2H507 



NH4NO3 



NH4CI 



(NH4)oS04 



.1 M 

 .1 M 

 .005 M 

 .1 M 



.05 M 



.01 M 



.1 M 

 .01 M 



.1 M 

 .01 M 



.1 M 

 .01 M 



.1 M 

 .01 M 







++++ 



++++ 

 ++++ 

 ++++ 



+ 

 + 



+ 



+ 

 + 



+ 

 



Distilled water 

 (control) . . . . 



' = no visible blueing 

 + = very slight blueing 

 ++ = slight blueing 

 +++ = moderate blueing 

 + I M = heavy blueing 



Fe(NH4)2(S04)2 to crab meat obtained from 

 various processing plants and on every occa- 

 sion the meat turned blue. These results dem- 

 onstrated beyond any reasonable doubt that 

 Fe++ and/or Fe+++ ions are responsible for 

 blue discoloration in canned crab meat. 



Apparently, at some time during the life of 

 the crab or during the processing procedure, 

 the meat is exposed to or contaminated with a 

 relatively high concentration of iron. Whether 

 the contamination comes from processing tech- 

 niques or is inherent to the crab is open to 

 conjecture. One possible source is through 

 airborne contamination. Thompson and Farra- 

 gut (1969) determined that airborne metallic 

 particles were responsible for green discolor- 

 ation in frozen raw breaded shrimp. Iron 

 processing baskets are often used. Pollution 

 of the waters which the crabs inhabit cannot 

 be ruled out. Whatever the cause, blueing 

 occurs spontaneously and sporadically. 



