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

ice there was only a small margin (different) of about 1 log10 cfu/cm 2 in both parameters on
the skin prior to wash between the three factories (establishments). The levels of TVC counts
reflect that whole fish was stored in ice for considerably time. In accordance with ICMSF,
(1986), normal micro flora counts on the skin of fish at the time of harvest are in the region
of 10 2 – 10 5 organisms per gram while an increase to levels of > 10 6 per gram indicates long
storage in ice (chill conditions). During storage in ice, the bacteria loads, blood and slimes
on skin are continuously washed away by melting ice. The Total viable counts (prior-wash)
in this study are within the range reported by Adams and Moss (2008); Shewan (1962);
ICMSF (1980b); and Liston et al., (1976); that, the bacterial loads on the skin of fish from
catch can range from hundreds up to millions per square centimetres (10 2 -10 7 numbers/cm 2 )
of skin. Gibson and Ogden, 1987; and Dalgaard and Huss, 1994), showed that the slow
increase in counts may be caused by effect of ice where by it retards the growth of
microorganisms to less than one-tenth of the rate at optimal growth rates. While compared
with the relative growth rate of microorganisms at 20-30 o C which is approximately 25 times
higher than at 0 o C. The effect of washing whole fish on reducing bacterial loads was more
significant for Enterobacteriaceae than for total viable counts. There were more than 1 log10
cfu/cm 2 decreases after wash in Enterobacteriaceae at all three establishments but only in
one establishment in TVC counts. Hence these results reveal a good bacteriological
freshness quality of whole fish for processing as the counts were within the limits refered to
previously.
The results prior and after washing for online fillets corresponding to the above different fish
lots and establishments show some difference between establishments. Counts prior to fillets
washing were 2,91 – 4,55 log10 cfu/g (Enterobacteriaceae) and 5,49 – 6,27 log10 cfu/g (TVC).
A guideline on TVC level for fresh fish and fish products microbiological quality including
fillets is 5x10 5 -10 7 colony forming units per gram (cfu/g) of muscle (ICMSF, 1986) and for
Enterobacteriaceae ≤ 10 3 cfu/g of muscles (fillets). According to the results before washing,
the counts in 2 establishments were above levels of 10 3 cfu/g and in all 3 establishments above
5x10 5 cfu/g for Enterobacteriaceae and TVC respectively. This is indicating a likely
contamination and or growth of microorganisms during the subsequent processing steps at
establishments. However after wash the microbiological loads for E2 and E3 in fillets were
significantly reduced below the maximum allowable limits < 10 3 cfu/g (Ent.) and