August 1966 COMMERCIAL FISHERIES REVIEW 13 



EFFECT OF ROOM - TEMPERATURE INCUBATION ON THIAMINASE DESTRUCTION : A 

 test was conducted (the results of which are not shown in the table) to determine the stability 

 of thiaminase at room -temperature incubation. Samples of ground whole alewife, carp, shad, 

 shiner, and smelt (at their natural pH) were sealed in T.D.T. cans and stored at 73°-83° F. 

 At monthly intervals, the samples were analyzed for residual activity. The samples, of 

 course, were putrid when analyzed, and all the cans were greatly distended. Carp, shad, and 

 shiner gave a positive thiaminase test even after 3 months of incubation. Smelt, which had a 

 low initial enzyme activity, was inactive at the end of one month. Alewife, which was incubated 

 for only 2 months, was still active at the end of that time. These results suggest that the 

 thiaminase enzyme is not readily destroyed at room temperature by the various proteolytic 

 enzymes of fish. 



EFFECT OF ENZYME CONCENTRATION ON THIAMINASE DESTRUCTION : The intital 

 activities of the unheated raw fish samples are expressed as the number of micrograms of 

 thiamine hydrochloride destroyed per gram of protein in 20 minutes under the conditions of 

 the assay procedure. The values are expressed on a protein basis so that some standard ref- 

 erence point can be assumed and comparisons between species can be made more meaning- 

 fully. As was indicated in a preceding paragraph, the initial activity of the raw fish is not 

 necessarily related to the time required to destroy the enzyme when different species are 

 compared. However, enzyme activity appears to be related to processing time when a single 

 species is considered. Alewife viscera, for example, which had an initial activity of 572, re- 

 quired 46 minutes at 170° F. for total destruction of thiaminase; whereas, diluted alewife and 

 alewife fillets (initial activity of 152 units) required only 7 minutes at 170° F. 



EFFECT OF £H ON THIAMINASE DESTRUCTION : The pH values reported in the table 

 are of the raw unheated fish, except in the cases of Alewife B and Alewife C, which were ad- 

 justed to 5.9 and 8.2 with HCl and NaOH, respectively, prior to heat treatment. All values 

 were read by inserting the electrodes (glass and standard reference) of a pH meter into the 

 ground fish. The results obtained with Alewife A, Alewife B, and Alewife C indicate that pH 

 has some effect on thiaminase destruction. High pH tends to increase the heat lability of the 

 enzyme; whereas, low pH tends to decrease its heat lability. As with the effect of enzyme 

 concentration, the effect of pH was studied on only a single species, so no conclusions can be 

 drawn on its effects between species. 



CONCLUSIONS 



A minimum time-temperature relation of 5 minutes at 180° F. is required to destroy all 

 of the thiaminase in whole raw fish. At temperatures above 180° F., thiaminase is very heat 

 labile; only small differences are evident between species. At temperatures below 180° F., 

 however, the thiaminases of different species show marked differences in heat sensitivity. 

 These differences are as' yet unexplained, although they may be related in part to protection 

 against heat destruction by a high content of oil. 



Enzyme concentration (as determined by the initial activity in the raw fish) is not neces- 

 sarily related to processing time when different species are compared, but it is related to 

 processing time when members of a single species are compared. 



The effects of pH on heat sensitivity of thiaminase was studied on alewife only. High pH 

 tended to increase the heat lability of thiaminase; low pH tended to decrease the heat lability. 



The thiaminase of canned raw fish, stored at room temperature, can remain active for at 

 least 3 months. 



REFERENCES 



ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS 



1960. Official Methods of Analysis . Association of Official 

 Agricultural Chemists, Washington, D, C, 9th Ed, 



BORCSTROM, GEORGE 



1962. Fish as Food , vol. U, p. 438. Academic Press, Inc. 

 Ill Fifth Ave,, New York, N, Y. 10003 



DEUTSCH, H. F. AND A. D. HALSER 



1943. Distribution of a Vitamin B^ Destructive Enzyme in Fish, 

 Proc. Soc, Exp . Biol . Med,, vol. 53, p. 63-65, 



GNAEDINGER, R. H. 



1964. Thiaminase Activity in Fish; An improved assay method. 

 Fishery Industrial Research , vol. 2, no. 4, pp. 55-59. 



