Blueing of Processed Crab Meat. 



II. Identification of Some Factors Involved in the 



Blue Discoloration of Canned Crab Meat (Callinecfes sapidus) 



By 



MELVIN E. WATERS, Research Food Technologist 



National Marine Fisheries Service Fishery Products Technology Laboratory 



Pascagoula, Mississippi 39567 



ABSTRACT 



An outbreak of blue discoloration in canned crab meat occurred during 1969. This 

 paper reports the result of a study we made to pinpoint the cause of blueing and sug- 

 gest a remedy. Factors found not to affect the color of canned crab meat are (1) 

 method of obtaining a vacuum, (2) the use of a parchment liner, (3) plant water used 

 in processing, (4) the use of dead and/or partially dead crabs, and (5) several metal 

 ions reported as the cause of blueing in other products. 



Results showed that iron was involved in the discoloration. It was further shown 

 that a buffered solution of citric acid (pH 6.5-6.8) prevented formation of the blue- 

 colored complex. 



INTRODUCTION 



In early summer of 1969 during the begin- 

 ning of the canned crab meat production 

 season on the Gulf coast, a local processor 

 experienced an outbreak of severe blue dis- 

 coloration in his canned product. The discov- 

 ery was made some 72 hr after processing and 

 was the first noted for the season. A close 

 examination of the product revealed that (1) 

 the blue discoloration was typical of that oc- 

 casionally found in canned crab meat, (2) the 

 discoloration was not limited to any particular 

 area of the can, (3) there was no evidence of 

 can corrosion at the seams, (4) not all fibres 

 of meat were affected nor was the entire fibre 

 always affected, and (5) the pH of the meat 

 was considerably higher than that normally 

 found in routine production when additives 

 were used. 



After the discovery of this discoloration, a 

 check made of subsequent production showed 

 (1) no evidence of discoloration and (2) a 

 lower pH than that in the affected crab meat. 

 The outbreak in this producer's pack was con- 

 fined to one day's production. We concluded 

 that someone inadvertently left out the addi- 

 tives (or a portion thereof) normally added to 

 prevent blueing. 



A survey of other processors in the area 

 showed that several of the processors were ex- 

 periencing discoloration of the product. The 

 raw material used was supplied from a wide 

 geographical area. The blue discoloration was 

 particularly prevalent in claw meat taken from 

 Texas crabs. We also learned that a severe 

 outbreak, such as that described above, had not 

 occurred for some 7 or 8 years. The industry 

 as a whole is affected at one time or another; 

 consequently, it asked our help in determining 

 the cause and suggesting a remedy. 



