Evaluation of total volatile bases and trimethylamine in hake (Merluccius capensis) fish preserved at low temperature in Vanderbijlpark, South Africa

Fish is one of the most highly perishable food product and its quality aspects are of significance to retailers and consumers. The purpose of this study was to investigate the change in quality of hake (Merluccius capensis) fish preserved at -14°C over a period of seven weeks in other to evaluate fish spoilage indicators. The fish quality parameters assessed were pH, trimethylamine nitrogen (TMA-N) and total volatile bases nitrogen (TVB-N). The data revealed that there was an increase in pH from 7.4 to 7.7 during the storage period. The concentration of TVB-N in the hake samples increased from 7.21 to 23.35 (± 0.036) mg-N/100g while that of TMA-N increased from (range: mean ± std) 3.18 - 3.34: 3.25 ± 0.068 to 13.90 – 15.01: 14.29± 0.493 mg-N/100 g within the seven weeks of preservation, with percent increase of 69.13% (TVB-N) and 77.26% (TMA-N) of the initial amount. The overall data exhibited a steady and consistent increase in the amount of TVB-N, TMA-N and pH in the flesh of hake fish preserved at the temperature and duration of the study. This steady increase in these chemical parameters is a significant potent warning to consumers to resist lengthy storage of fresh fish and its products before consumption. One-way analysis of variance was adopted to assess the validity of the parallel increase of TVB-N, TMA-N, pH with storage duration at low temperature and the analysis revealed no significant differences between increase in the three chemical parameters and storage time. In other words increase in TVB-N, TMA-N, pH content is directly proportional to the increase in storage time. This study have provided useful data to benefit South African retailers on storage and maintenance of TVB-N and TMA-N limits of acceptance in the consumption quality of hake to be sold to consumers and  also for consumers on storage duration of hake in their refrigerators before consumption.