A new chemical criterion for the quality control of fish: trimethylamine/total volatile basic nitrogen (%)

Trimethylamine (TMA) and the total volatile basic nitrogen (TVBN) were determined in 169 samples of sea-fish (herring, cod, whiting, and mackerel) at all stages of decomposition. The comparison of these two parameters with the ratio P=TVBN/TMA (%) showed that P provides a useful index of freshness. It is relatively constant between species, its dispersion is less than that of TMA and it increases more rapidly than TVBN at the start of decomposition. Statistical analysis of the experimental results showed that there is a non-linear correlation between P and the decomposition index (i). The comparison of the line-equations defining log P as a function of i for different species of marine Teleostei led us to show that there is little or no intrapsace variation of this correlation under determined conservation conditions. It is noted that for a given species, this correlation is temperature-dependent. Statistical exploitation of these results permit us to determine the maximal admissible values for P which can be used as a support for the development of new standards