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

(around 6 log10 cfu/g) after 12 storage days regardless of the longer storage time of whole
Nile perch in ice prior processing at establishments. The long shelf life of fillets with initial
high counts of > 4 log10 cfu/g can be explained by the lower psycrophilic counts in
tropical/fresh water fish compared to temprate water fish (Disney (1976) and Shwewan
(1977).
Total volatile base nitrogen changes were small and parallel with the Enterobacteriaceae
counts during the first 12 days of storage. The increase in TVB-N levels depend on
numbers of SSO, H2S (black colonies) producing bacteria i.e. Aeromonas and Shewanella
(Gram et al., 1990). Likewise Enterobacteriaceae and non H2S (white colonies) producing
bacteria which include Pseudomonas, Alcaligens, Moraxella, and Acinetobacter can also
produce TVB-N (Gram et al., 1987). In all spoilage micro flora and chemical changes were
rapid after 12 days of storage. This means bacterial activity in the fish flesh leads to
accumulation of TVB-N. The TVB-N content include TMA which is produced by bacteria
when they are at higher numbers i.e. ≥ 10 8 -10 9 cfu/g (Chytiri et al., 2004; Rehbein and
Oehbeinschlager, 1982).
5.3.2.2 Establishment E2 (17 days iced whole Nile perch)
Estimated storage life for the fillets based on the spoilage microbiological (SSO and TVC)
counts is 8 days. This brings into attention that Nile perch fillets that are aimed to be stored
for a long time i.e. (>10 days) should be processed from a fish stored in ice for a maximum
of 10-14 days. In Establishment E2 the whole fish had been stored in ice for 17 days prior
to processing. Here the fillets showed a spontaneously log phase from the beginning of
storage to the end with highest counts up to > 10 log10 cfu/g which has rarely been reported.
The ICMSF, (1980b), reported four stages of fresh fish when stored in ice (table 4). At
stage IV (> 14 storage days in ice) microbiological counts may reach ≥ 10 8 cfu/cm 2 and
remain constant during the remaining storage time. The same was observed in the present
work and also in a study by Gram et al., (1989). Although super chilling treatment may
have arrested or killed most of the microbial load there are still many which have survived
and can account for the fast multiplication to levels beyond 10 log10 cfu/g within 2 weeks of
storage. This period (2 weeks) is declared by processors as the maximum shelf life/storage
time for chilled fillets. However, it is important to fulfill the markets/ consumers
requirements with respect to set shelf life as well as means of transportation and storage
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