Odors and tastes are difficult to describe and there are no 

 absolutes on which to base a decision. To become an expert in the de- 

 tection of physical deterioration of shrimp, one miost be familiar with 

 the odor and appearance of the normal, unspoiled product. The quality- 

 inspector must have an opportunity to observe the decomposition of 

 shrimp under conditions as nearly identical as possible to commercial 

 practices. He must familiarize himself with the prodxiction processes 

 for all types of processed shrimp and study the changes which take place 

 as a result of these processes, since the odors of decomposition are 

 often partly dissipated or chanf^ed in the processing. Only repeated 

 tests will enable the expert to put reliance on his senses in making the 

 distinction between the spoiled and unspoiled product. 



Chemical Analysis 



In recognition of the fact that there is room .for honest dis- 

 agreement among experts in subjective examination, there have been many 

 investigations aimed at improving the method of chemical analysis, 

 /cceptable chemical tests are readily reproducible in the hands of dif- 

 ferent analysts and are not affected by such factors as fatigue, time 

 lag, emotional experience, foreign .odors, etc. Many substances have been 

 considered for measuring decomposition. A number of requirements have to 

 be met before a compound can be used as an index of decomposition. For 

 example: the volatile sulfur compounds in shrimp once appeared to be 

 very useful; however, two serious objections were raised to their use. 

 Sulfiir compounds united with the can lining in a persistent and unpre- 

 dictable manner and some waters used by the shrimp canners contained 

 enough of such compounds to make the results unreliable. 



It is mandatory that the substance selected as an index should 

 not be present in sound food, or if so, only in a small and reasonably 

 constant quantity. The ideal index would iir^sart some, if not most, of 

 the odor or taste which is recognized by subjective inspection and should 

 lend itself to comparatively simple and rapid isolation, identification, 

 aind measTirement procedures. To be most useful, the substance should not 

 be affected by processing or subsequent storage. No index meeting all 

 of these criteria has yet been found for detecting decomposition in any 

 food. 



There are substances, however, which meet enough of these re- 

 quirements to prove very valuable to the food chemists. Indole §''has 

 been used for several years as a means of measuring decon^josition in 

 shrimp and other shellfish. Indole results from bacterial action on 

 tryptophan, one of the amino acids found in the protein of seafood. 

 Absolutely fresh shrimp and oysters do not contain measurable amounts of 

 indole, although the test is capable of detecting as little as five 



^ For chemical method see Journal of the Association of Official 

 Agricultural Chemists, May 19U6, "Indole in Shrimp", R, F, Dugan 

 and L. W. Stras burger. 



79 



