Evaluation of histamine-producing bacteria in cold-smoked mackerel (Scomber scombrus) retailed in Ota, Ogun State, Nigeria

Abstract

Background: The occurrence of histamine-producing bacteria (HPB) in poorly preserved mackerel fish smoked and retailed in the majority of   Nigerian markets is of public health concern and therefore necessitated this investigation. Objectives: The aim of this study was to evaluate histamine-producing bacteria in cold-smoked mackerel (Scomber scombrus) retailed in Ota, Ogun State, Nigeria. Methods: Cold-smoked mackerel fish samples (36 pieces) were purchased from four selected markets in Ota: Oju-Ore (OJ), Iyana-Iyesi (IY) Iju (IJ) and Oja Oba (OO). Each of the fish samples cut into Head (H), Trunk (Tr) and Tail (Tl) were analyzed for microbial loads; total plate count (TPC; log CFUg^-1) and histamine-producing bacteria (HPB; log CFUg^‑1) using pour plate method of isolation. Data were generated in triplicates and analyzed using ANOVA and Duncan’s multiple range at α 0.05. Results: The microbial loads showed that all the fish samples were of unsatisfactory microbial quality having mean counts of ≥ 10⁷, with the highest TPC values of 8.59±0.17, 8.44±0.47 and 8.43±0.21 log CFUg^-1 respectively recorded in TL, TR and H parts. Iyana-Iyesi market recorded the least (7.80±0.51 (TL) to 7.89±0.35 (H) log CFU/g) while Iju market had the highest value range of 8.43±0.21 (H) to 8.59±0.17 (TL). Pseudomonas spp. (45%, 299 colonies), Proteus spp. (24%, 130 colonies), Escherichia coli (20%, 157 colonies) and Morganella morganii (11%, 95 colonies) were the isolated HPB. Conclusion: This indicates that the safety of smoked mackerel fish retailed in Ota is compromised and may therefore be unsafe for human consumption. This information can be useful for critical monitoring to improve their quality and safety.

Keywords: Cold-smoked, Erratic electricity supply, Histamine-producing bacteria, Mackerel fish, Poor cold storage