August 1966 COMMERCIAL FISHERIES REVIEW U 



HEAT INACTIVATION OF THIAMINASE IN WHOLE FISH 



By R. H. Gnaedinger and R. A. Krzeczkowski* 



ABSTRACT 



The time required at various temperatures to inactivate all of the thiaminase in 

 several species of whole fish was studied. Some effects of pH and enzyme concentra- 

 tion on the time-temperature inactivation were also determined. Whole raw fish 

 were ground, sealed in specially-constructed metal cans, heated at various tempera- 

 tures for various lengths of time, and analyzed for residual thiaminase activity. Re- 

 sults indicate that a minimum time-temperature of 5 minutes at 180° F. is required 

 to inactivate all the thiaminase of whole fish. Enzyme concentrations, pH, and pos- 

 sibly oil content of fish influence the time required to destroy thiaminase. 



INTRODUCTION 



The heating conditions employed by commercial mink-food producers and mink ranchers 

 to destroy thiaminase in whole fish are empirical. The conditions are not based on predeter- 

 mined time -temperature relations for the thermal inactivation of this antimetabolite. A com- 

 mon practice, for example, is to cook the fish at 1800-200° F. for 15 minutes (Borgstrom 1962). 



Most of the specific data available on the time-teinperature relation is found in various 

 research publications dealing with the occurrence of thiaminase in fish, or with studies on the 

 chemistry of the enzyme. Deutsch and Hasler (1943) used 15 minutes at 100° C. (2120 p_) to 

 inactivate thiaminase in whole fish and viscera homogenates . Sealock, Livermore, and Evans 

 (1943) destroyed most of the thiaminase in carp by heating at 100° C. for 30 minutes. They 

 found that with dilute or purified preparations, thiaminase can be destroyed completely in a 

 bath of boiling watfer in 5 minutes. Melnick, Hochberg, and Oser (1945) used 20 minutes at 

 100° C. to destroy thiaminase in ground fish suspended in water at pH 4.5. Somogyi (1949) 

 used only 10 minutes at 100° C. to destroy the thiaminase in a carp intestinal extract. Simi- 

 larly, Kuusi (1963) used 10-30 minutes in a bath of boiling water to inactivate thiaminase in 

 Baltic herring and bream. 



The time -temperature conditions used by those researchers can be used, however, only 

 as general guidelines by commercial processors. There appears to be no published data re- 

 garding minimum times and temperatures that are sufficient to inactivate all of the thiami- 

 nase in whole fish. Such data would be important in the development of improved fish-reduc- 

 tion methods that are designed to yield safe, high-quality products. 



The purpose of this study was to determine minimum time -temperature relations re- 

 quired to inactivate all of the thiaminase in several species of fresh-water fish. Some effects 

 of pH and enzyme concentration on time -temperature relations were also studied. 



EXPERIMENTAL 



PREPARATION OF WHOLE - FISH SAMPLES : Fresh whole fish were passed twice through 

 a meat grinder, first using a i-inch plate and finally using a i-inch plate. The homogenous 

 ground material was then immediately packed and sealed in metal 208 x 006 Thermal Death 

 Time (T.D.T.) cans, was frozen, and stored at 0° F. until used. Sufficient ground material 

 was used so that no air space remained in the cans. These cans (which have a capacity of a- 

 bout 20 grams) are specially constructed so that the entire contents can be heated (or cooled) 

 very rapidly and uniformly, thereby eliminating the need to measure the internal temperature 

 of the cans; thus, the internal temperature is assumed to be equal to the temperature of the 

 heating medium. 



♦Chemists, Technological Laboratory, U,S, Department of the Interior, Bureau of Comnaercial Fisheries, Ann Arbor, Mich, 



S. DEPARTMENT OF THE INTERIOR 

 Fish and Wildlife Service 

 Sep. No. 769 



