millionths of a gram. Unfortunately for the food chemist, only certain 

 bacteria produce indole from tryptophan; therefore, shrimp may be decom- 

 posed and have little or no detectable indole present. So far the indole 

 method has been used only to support the testimony of an expert who has 

 made a subjective identification of spoilage. 



Taste Panel Testing 



As an example of taste panel testing, a recent laboratory 

 experiment based on 5 different lots of shrimp revealed information with 

 respect to periods of maximuin safe storage of iced shrimp. 



Fresh caught shrimp retained their fresh sweet flavor during 

 the first 5 days of ice storage. From the sixth to the eighth day of 

 storage the shrimp rapidly lost their sweet flavor and became taste- 

 less ("stale shrimp"). From the eighth to the twelfth day of storage 

 the shrimp were tasteless but no off -odors or flavors were evident. 

 After 12 days of ice storage, spoilage took place and the cooked meats 

 had off -odors and flanrors. The results obtained from the use of the 

 chemical tests were in substantial agreement with those obtained from 

 taste panel testing. 



Frozen shrimp which are stored at 0° F. (-13° C.) lose their 

 quality very slowly. Both the quality of frozen shrimp and the length 

 of time they remain an acceptable product during frozen storage is 

 affected by the length of time that the shrimp are stored in ice prior 

 to freezing. Taste panel testing is more effective in discovering 

 quality differences resulting from differences in length of time of 

 iced storage prior to freezing than chemical testing. Chemical tests 

 showed only minor changes in quality over a 12Hnonth period for samples 

 of frozen shrimp stored in ice, 1, 6, and 12 days prior to freezing. 

 A taste panel group, however, was able to detect marked differences 

 between these samples after relatively short periods of storage. The 

 longer shrimp were stored in ice before freezing, the poorer the quality 

 of the frozen product. 



Ultraviolet Light 



A method of quality determination which differs from the ones 

 described above involves the stucfy of changes in the fluorescence in- 

 duced by ultraviolet ("black") li^t in iced shrimp. According to 

 experiments, any shrimp which shows brilliant white fluorescence of 

 the tissues at the headed end or elsewhere when peeled and exposed to 

 ultraviolet light of about 2,570 angstoras, can be graded as spoiled 

 or rapidly spoiling. A faint white fluorescence in the headed region 

 indicates the first onset of spoilage. In the experimentsjthe white 

 fluorescence generally occurred after 6 to 10 days when the shrimp had 

 been held in "Rickey" type ice. It was thought that buyers could use 

 the method for testing shrimp samples at the dock or from shipments of 

 iced shrimp delivered to processing plants. 



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