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

NH3 Ammonia amino acids and urea
Acetate, CO2 (carbon dioxide), H2O
(Water)
14
carbohydrate and lactate
Esters, ketones, aldehydes amino-acids (glycine, serine, leucine)
2.3.2 Biochemical spoilage of fresh fish
Fish is very perishable, high protein food which contains high level of amino acids. Total
volatile basic amines (TVBA), a general term which includes trimethylamine,
dimethylamine, ammonia and other total volatile basic nitrogenous (TVB-N) are
compounds associated with seafood spoilage. The levels of TVB-N and TMAO are
different from each fish species and even in different parts of the fish. The TVB-N consists
of ammonia (NH3), monomethylamine (MMA), dimethylamine (DMA), and
trimethylamine (TMA). Their levels may change during bacterial activity and or enzymic
degradation of trimethylamine oxide (TMAO) in fish. Marine fish and some freshwater fish
contain trymethylamine oxide (TMAO) which is degraded by majority of spoilage microbes
to trimethylamine (TMA). The SSOs utilizes the available TMAO in anaerobic respiration
and produces off-odours and off-flavours following the formation of TMA, (Huss and
Larsen, 1980; Gram et al., 1987, 1990; Dalgaard et al,. 1993). Sulphur containing amino
acids; cysteine and methionine decompose to liberate off-odours and off-flavours; hydrogen
sulphides and methylmercaptane; aldehydes, ketones, esters, hypoxanthine as well as other
low molecular weight compounds in spoiling fish, Herbert and Shewan, (1975, 1976);
Ringo et al., (1974) and Shewan, (1962).
Karnicki and Lima Dos Santos, (1985) reported estimates of TVB-N in Nile perch fillets
stored for two days at ambient temperature in tightly closed bag to have initial value of
48.5 mg N/100g rising to 60.2 mg N/100g. TVB-N values for cod stored in ice are 35-40
mg N/100g, (Ozogul, 2000) and levels of 30-35 mg N/100g (Connell, 1995 and Huss,
1988) which have been considered the limits of acceptability for ice stored cold water fish.
Therefore TVB-N values above these are regarded to indicate spoilage of the fish stored in
ice.
Ammonia (NH3) has been identified as a volatile component in a variety of spoiling fishes. It
is formed by the bacterial degradation/ deamination of proteins, peptides and amino acids as