[Quality changes in iced shrimps (Pandalus borealis). II Changes in the contents of trimethylamine oxide and volatile nitrogen bases during automatic boiling and peeling (author's transl)].

Post mortem trimethylamine oxide (TMAO) in marine animals is reduced to trimethylamine (TMA), and the degradation of proteins causes an increase in the ammonia (NH3) content. During ice-storage NH3 and TMA usually make up the major part of the total content of volatile nitrogen bases (TVN) which are formed during the degradation process. The formation of TMA and NH3 is probably caused mainly by bacterial enzymes. The contents of TMA and TVN in marine fish and shrimps are important objective criteria in supporting organoleptic examinations of such raw materials. During automatic boiling, peeling and rinsing processes in shrimp factories, some of these water-soluble and volatile compounds will be extracted by the boiling water and possibly evaporated. In this investigation we have attempted to estimate the loss of TMAO, TMA and TVN in shrimp muscle during this automatic processing. The investigation includes experiments in the laboratory (Table I, Figure 1) and in two factories (Table II-III, Figure 2-3). The results show that about 50% of the contents of TMAO-N, TMA-N and TVN probably will be lost from the shrimps during automatic processing. Adding approximately 100% TMA-N and TVN to the analysed contents in boiled, peeled and rinsed shrimps will therefore probably give the same level of these compounds as that found in the raw shrimps used. An accurate measurement of the TMA- and TVN-content in shrimp produced under known condition in North-Norwegian shrimps factories could give an objective indication of the quality of the raw shrimps used. In accordance with Norwegian shrimp regulations, only the fresh, healthy shrimps are allowed to be produced.