Trimethylamine and Total Volatile Basic Nitrogen Determination by Flow Injection/Gas Diffusion in Mediterranean Hake (Merluccius merluccius)

The reliability of flow injection/gas diffusion (FIGD) methods to determine trimethylamine (TMA-N) and total volatile basic nitrogen (TVB-N) in hake was studied in order to find an alternative and accurate, simple, cheap, and rapid method for non-protein nitrogen determination. FIGD methods involved extracting volatile amines with 7.5% trichloroacetic acid, followed by the injection of the extracts into the FIGD manifold, previously adjusted for TMA-N or TVB-N determinations. Each determination took approximately 2 min. Reliability was satisfactory in linearity, precision, recovery, and sensitivity. There was good correlation (p < 0.001) between FIGD and the classic official methods, for both TMA-N and TVB-N determinations, and also between FIGD and the gas chromatographic procedure described for TMA-N. These results proved that FIGD methods are simpler, cheaper, and faster than current official procedures. To check the suitability of FIGD procedures over a wide range of analyte concentrations, changes of both TMA-N and TVB-N and the P ratio values throughout the ice storage of hake were monitored. The usefulness of each of these potential freshness indicators for hake is discussed.