Determination of trimethylamine nitrogen and total volatile basic nitrogen in fresh fish by flow injection analysis

There are many chemical, microbiological and sensory indices of fish quality. Of the chemical indices, TMA-N and TVB-N are probably the most used in connection with remaining shelf-life determination. This paper reports on a study of modifications to a flow injection analysis (FIA) method necessary to make it suitable for TMA-N and TVB-N determination, specifically the optimal concentrations of NaOH and formaldehyde for releasing the volatile bases from the acidic fish extract and sequestering the non-TMA volatile bases respectively. The effects of using perchloric acid (PCA) and trichloroacetic acid (TCA) as fish extractants were also investigated. The fish species used were monkfish (Lophius piscatorius), skate (Raia clavata) and cod (Gadus morrhua). It was found that 1 M NaOH was the optimal concentration for volatile base release and that 200 g l⁻¹ formaldehyde was adequate for non-TMA base sequestration. Use of PCA and TCA as fish extractants appeared to have no significant effect on TMA-N and TVB-N determinations. © 1999 Society of Chemical Industry