Microbial quality of Nile perch (Lates niloticus) and physico-chemical properties of salted sun-dried products sold at regional markets, Tanzania

This study was conducted to investigate the microbial and physico-chemical qualities of salted sun-dried Nile perch (Lates niloticus) products and frozen fish from various storage facilities in Mwanza, Tanzania. The bacterial flora, moisture contents (MCs), and water activity (Aw) were investigated using standard methods. A total of 120 samples were collected for microbiological analysis with 90 of the samples additionally analysed for MC and Aw. Findings showed that the mean total viable counts (TVCs) in salted sun-dried products sampled during rainy season was 4.5 log cfu/g in fish heads with MCs of 38.0% and Aw of 0.682. This was significantly higher (P<0.05) than what was recorded during the dry season with mean TVCs of 3.0 log cfu/g at MCs of 24.6% and Aw of 0.625. Fish chests had TVCs of 3.3 log cfu/g and MCs of 27.6% and Aw of 0.659 in rainy season with no significant seasonal difference (P>0.05). Fish belly flaps had TVCs of 3.3 log cfu/g at 26.4% MCs and 0.669 Aw in rainy season which were comparable (P>0.05) to those dried in the dry season. The microbial species recovered were Staphylococcus spp., Enterobacter spp., Psychrobacter spp., and Bacillus spp. Neither Escherichia coli nor extended-spectrum beta-lactamase producing Enterobacteriaceae were detected. Frozen Nile perch had TVCs of 5.7 log cfu/g on skin, 5.4 log cfu/g in gills and 2.9 log cfu/g in flesh and were within acceptable limit set by Tanzanian standards. These results reveal that dried Nile perch products are generally safe for human consumption; however, the recovered bacteria indicate a need of implementing hygienic procedures during processing of products for improved quality and safety.