A CRITICAL REVIEW OF TOTAL VOLATILE BASES AND TRIMETHYLAMINE AS INDICES OF FRESHNESS OF FISH. Part 1.

The large literature on the formation of volatile amines, and of their aggregation as Total Volatile Base (TVB), during spoilage of vertebrate, teleostean fish in ice, and their used as indices of freshness is critically reviewed. This part reviews analytical procedures. The thermodynamics of the distillation process in determining TVB is reviewed and optimum conditions for the distillation are considered. Distillation other than at temperatures below about 50°C is accompanied by decomposition of nitrogen-containing compounds with the formation of ammonia additional to the intrinsic ammonia in the sample. The amount of decomposition differs among the various procedures used for determining TVB. Rapid distillation in automated distillation units produces the smallest amount of decomposition. Trimethylamine (TMA) is often determined by the picrate method, but this is not completely specific for TMA and some dimethylamine is included in the result depending of the alkali and the amount of formaldehyde used. Other analytical techniques such as GLC and Flow Injection Analysis are specific and are to be preferred for critical work. There are differences among procedures for determining TVB and TMA in the way concentrations in the sample are calculated when using protein-free extracts which leads to biases between methods.