Microbiology and Spoilage Trail in Nile Perch (Lates niloticus), Lake ...

3.3.2.1.3 Phase I – Trial 3: Whole Nile perch
Volume of 200ml (equivalent to 200g) of diluents (0.1% peptone and 0.85% salt solution)
was used to rinse individual fish samples placed in polyethylene bags. The rinse solutions
were treated as undiluted test samples. Volumes of 25ml of rinse solutions were added to
225ml of Buffered peptone water (BPW) enrichment medium for detection of Salmonella.
Similar volumes (25ml rinsed diluents) were added to 225ml of Alkaline peptone water
(APW) enrichment medium for pathogenic Vibrio spp. Subsequent analytical steps (in
3.3.2.1.1.) as for water analyses above were then followed for the Salmonella and Vibrio
analysis.
For examination of TVC and Enterobacteriaceae in fish guts 20g of fish guts were weighed
into 180ml of diluents and stomached in 400 stomacher for 1 minute to make 1/10 dilution.
Serial dilutions up to 1/1000 were made. Then subsequent analytical steps as for water and
sediments analyses (3.3.2.1.1 and 3.3.2.1.2) used above were then followed.
3.3.2.2 Phase II: Laboratory- shelf life for iced whole Nile perch and chilled Nile perch
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fillets
3.3.2.2.1 Phase II trial 1: Shelf life of iced whole Nile perch
Samples were sampled on different days: 4, 7, 10, 13, 15, 20, 22, 26, 28, 30 and 33 storage
days in laboratory refrigerator at 0-3 o C, see appendix III -A.Whole Nile perch samples were
sampled and put into polyethylene bag, then stored in the laboratory refrigerator at 0-3°C
prior to analysis. The laboratory samples were prepared according to NMKL method #91,
(2002). Plate Count Analysis was done according to the Iron agar (IA) method, (Gram et al.,
1987). The composition of the IA agar consists of the following ingredients:
• Peptone bacteriological (Oxoid LP0037B)
• Bacteriological agar –No.1 (Oxoid LP00113B)
• Yeast extract granules (Merck VM284953)
• Beef extract powder (Highmedia RM002)
• Ferric citrate salt
• Sodium thiosulphate
• Sodium chloride