July 1951 COMMERCIAL FISHSRIES REVIEW 5 



EFFECT OF ASCORBIC ACID ON KEEPING 

 QUALITY OF FROZEN OYSTERS 



By S. R. Pottinger* 



ABSTRACT 



SHUCKED OYSTERS WERE TREATED WITH ASCORBIC ACID IN AN ATTEMPT TO 

 PREVENT OR RETARD DARKENING AND OTHER UNDESIRABLE CHANGES DURING FROZEN 

 STORAGE ON THE BASIS OF ORGANOLEPTIC TESTS, CHANGES I N TH E FROZEN 

 OYSTERS TREATED WITH ASCORBIC ACID WERE NOT APPRECIABLY RETARDED IN 

 COMPARISON WITH UNTREATED FROZEN OYSTERS USED AS CONTROLS. 



INTRODUCTION 



Packers and distributors have from time to time encountered difficulties due to 

 color changes in frozen oysters. These changes are variously described as "darken- 

 ing," "discoloration," or "browniiig," and occur during frozen storage. This darken- 

 ing 'v;as also noticed in past studies of frozen oysters by the U. S. Fish and Wildlife 

 Service. 



The cause of these changes in color in oysters is not definitely knovm. It is 

 known, however, that enzymatic action will cause undesirable changes in the odor and 

 flavor of frozen fish and under certain conditions, will also cause color changes on 

 the surface of the fish. Possibly a similar reaction occurs in frozen oysters. 



Earlier work (Bauernfeind, et al, I948; Tarr, I946 and I948) indicated that as- 

 sorbic acid is a practical antioxidant in retarding discoloration and undesirable 

 flavor changes during freezing and frozen storage of certain types of fish. In sim- 

 ilar work with oysters, conflicting results have been reported as to whether ascorbic 

 acid is effective in maintaining quality and retarding the darkening of oysters dur- 

 ing frozen storage. 



In order to investigate further the effectiveness of this antioxidant in this 

 respect, a series of tests with frozen oysters were made at the Service's College 

 Park, Maryland, laboratory. Prior to beginning the tests, discussions were held 

 with repi-esentatives of manufacturers of ascorbic acid in order to benefit from their 

 experience with previous work along these lines. The concentrations of ascorbic acid 

 used in these tests and the method of incorporating it with the oysters are based on 

 the information obtained through these discussions. 



PREPARATION OF SAMPLES 



Freshly prepared, commercially shucked oysters were obtained from an oyster- 

 packing house in the Chesapeake Bay area and brought, well packed in crushed ice, to 

 the College Park laboratory. They were divided into eight groups for preparation 

 prior to final freezing and storage. 



The samples were prepared as follows: 



GROUP A: THE FRESH SHUCKED OYSTERS WERE DIPPED IN ONE-PERCENT ASCORBIC 

 ACID SOLUTION (ONE POUND OF OYSTERS IN ONE QUART OF SOLUTION) FOR ONE 

 MINUTE, AND THEN DRAINED FOR ONE MINUTE ON A LABORATORY-SIZE SKIMMING 

 TABLE, 



♦technologist, fishery TECHNOLOGICAL LABORATORY, BRANCH OF COMMERCIAL FISHERIES, U. S. FISH AND 

 WILDLIFE SERVICE, COLLEGE PARK, MARYLAND. 



