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

Spoilage of food means to deprive it of its quality. In totality food spoilage is the results of
metabolic processes that cause food to be undesirable for human consumption, (Adams and
Moss, 2008; Doyle, 2007; Gram et al., 2002, 1996). Therefore, generally spoilage is a
subjective quality which means products may be accepted or rejected by one person while
the same product may neither be accepted nor rejected by another person. Despite of the
important role of microorganisms in food spoilage, the final decision for rejecting the
spoiled food product concerned relies on sensory evaluation, (Gram et al., 2002; Connell,
1975; and Reineccius, 1990). This is because the microbial spoilage is normally associated
with a sudden onset which is noticed at late stages of spoilage of products when they
(microbial growth) are at log phases or the exponential growth phases. Therefore, it is
easier to identify chemical compounds that are responsible for a particular sensory index
such as off odours than the responsible spoilage organisms.
According to Baird Parker, (2000) and Anonymous, (1985), the current world food post
harvest and/or slaughter losses due to microbial spoilage estimates is about 25% of total
food produced. This is a big loss which can be reduced if the ecology of specific spoilage
organisms is well understood and controlled. However, every food product consistit of its
own spoilage micro flora associated with the raw materials, or post contamination, effect of
central processing parameters and storage conditions.
2.3.1 Microbiological spoilage of fresh fish
Despite that muscles of fresh or live fish are sterile, it contains high load of bacteria on the
surface slime of the skin, on the gills and in the digestive tract. Bacterial loads on surfaces
(skin) of fish from catch can range from hundreds up to millions per square centimetre (10 2
– 10 7 /cm 2 ); and in the gills and intestines in the range of 10 3 – 10 9 /g (Adams and Moss,
2008; Shewan, 1962; ICMSF, 1980b; Liston et al., 1976). These bacteria include Gram-
negatives of the genera Pseudomonas, Shewanella, Psychrobacter, Vibrio, Flavobacterium,
and Cytophaga and some Gram-positives such as coryneforms and micrococci. When the
fish is dead, the immune system collapses and bacteria are able to multiply. The bacteria on
the skin surface to a large extent colonize the scale pockets and invade the flesh by moving
between the muscle fibres during storage. Spoilage bacteria dominate and contaminate the
flesh/muscles through damaged parts of flesh and cause rapid spoilage of fish. Murray and
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