12 



COMMERCIAL FISHERIES REVIEW 



Vol. 28, No. 8 



HEAT TREATMENT OF SAMPLES: The filled cans were removed from frozen storage 

 and equilibrated in an ice-water bath prior to their being heated; thus, the starting tempera- 

 ture was about 32° F. for all samples. The cans were then submerged in a thermostatically- 

 controlled water bath for the desired length of time and at the desired temperature. At the 

 end of the heating period, the cans were immediately placed again in the ice -water bath until 

 cooled. The samples were subsequently frozen and held at 0° F. until analyzed for residual 

 thiaminase activity. 



ANALYSES OF SAMPLES : Thiaminase analyses were carried out according to the pro- 

 cedure of Gnaedinger (1964). Proximate composition analyses were carried out according to 

 the Association of Official Agricultural Chemists Official Methods of Analysis (1960). 



RESULTS AND DISCUSSION 



The times required to inactivate all of the thiaminase in various species of whole fish at 

 various temperatures are shown in the table. In most cases, the results are reported as two 

 numbers (for example, 3-4, which indicates that some activity was observed at 3 minutes but 

 none at 4 minutes). Thiaminase activities of the unheated starting materials, the pH and prox- 

 imate composition of the raw fish, including date and location of their capture, are also in- 

 cluded in the table. 



Time-Temperature Relationships of Inactivating Thiaminase in Whole Fish | 



Species!/ 



Date of 

 Cacture 



Location 



pH 



Thiaminase 

 Activity 



Time to Inactivate Thianjinase at; 



Proximate Composition 



200" F. 



190°^?. 



180" F. 



170"F.ll60OF. 



150° F. 



Waterj Oil 1 Ash IProteii 











y 



206 







Bowfin 



1/-/64 



Arkansas 



6.60 



1-2 



1-2 



1-2 



4 



_ 



. 



76.161 1.54 



3..S8 



15.53 



:arp 



12/10/64 



Lake Erie 



6.75 



2,003 



2-3 



3-4 



4-5 



9-10 



105 



- 



71.59 



9.56 



3.15 



13.97 



ihad 



10/28/64 



Lake Erie 



6.65 



112 



2-3 



3-4 



4-5 



32 



. 



_ 



70.58 



14.16 



2.24 



12.01 



Jmelt 



10/28/64 



Lake Erie 



6.85 



47 



1 



1 



1 



1 



1 



1-2 



75,54 



7.60 



2,01 



12.71 



Shiner . 



12/3/64 



Lake Michigan 



6.70 



1,418 



1-2 



1-2 



1-2 



2-3 



4-5 



- 



69.90 



11.92 



2.22 



12.99 



Alewife A 



11/-/64 



Lake Michigan 



6.90 



173 



1-2 



2-3 



4-5 



26-27 



- 



_ 



71.99 



13.49 



1.89 



11.20 



Alewife B 



11/-/64 



Lake Michigan 



5.9 



124 



1-2 



2-3 



4-5 



74-75 



- 



- 



70.15 



13.30 



2.39 



11.87 



Alewife C 



11/-/64 



Lake Michigan 



8.2 



162 



1-2 



2-3 



3-4 



3-4 



- 



- 



70.63 



13.27 



2.82 



10.86 



Alewife fillets!/ 



11/ -/64 



Lake Michigan 



6.4 



152 



1-2 



1-2 



1-2 



6 



. 



- 



71.63 



13.78 



1.26 



11.72 



Alewife viscera4/ 



12/3/64 



Lake Michigan 



6.9 



572 



2-3 



3-4 



6-7 



45-46 



- 



- 



70.57 



16.15 



1.9fi 



9.34 



Alewife dilutedS/ 



11/-/64 



Lake Michigan 



6.9 



152 



1-2 



2-3 



3-4 



7 



- 



- 



85.38 



6.76 



1.06 



5.83 



1/Alewife (Pomolobus pseudoharenqusl; Bowfin (A 



jnia oalva); 



Carp(C 



y^prinus ( 



:arpiol; 



Shad (Dorosoma 



cepedianum); Smelt fOsmerus 



mordaxji Shiner (NoCropis hudsoniusj. 















2/Micrograms of thiamine hydrochloride destroye 



d in 20 minL 



tes per ( 



jram of 



protein 



of the unheated raw fish, | 



3/Low concentration of enzyme. 















4/High concentration of enzyme. 















EFFECT OF TIME AND TEMPERATURE ON THIAMINASE DESTRUCTION : The results 

 of this study indicate that a minimum time -temperature relation of 5 minutes at I8OO F. is 

 required to obtain a thiaminase-free product from whole raw fish. From the standpoint of 

 commercial application, this relation implies that the coldest part of any fish particle must be 

 held at 180° F. for at least 5 minutes at some time during processes relying upon heat to in- 

 activate the antimetabolite. When fish offal (rather than whole fish) is being processed, the 

 minimum time should be increased to at least 7 minutes at 180° F., as indicated by the results 

 obtained in the use of alewife viscera. 



At temperatures above 180° F., the thiaminases of different species of fish show relative- 

 ly small differences in their heat labilities. Below 180° F. however, marked differences begin 

 to appear. At 170° F., for example, the results indicate that the thiaminases of carp and shin- 

 er are destroyed much more readily than are those of whole alewife and shad, even though the 

 latter two species had relatively lower initial thiaminase activities. In smelt, the species with 

 the lowest activity, thiaminase was destroyed in less than 2 minutes, even at 150° F. Thus, 

 processing conditions for this species would probably not have to be as severe as, for example, 

 those for alewife. There was some indication that a very high oil content exerted a protective 

 action against heat destruction of thiaminase, although exceptions were evident, notably that 

 of the shiner. This species possessed both high initial activity and high oil content, but the 

 thiaminase was destroyed in 5 minutes even at 160° F. 



