Biology Reference
In-Depth Information
Microorganisms in Fermented/Salted Fish
Most fermented fi shery products are made from fatty fi sh. Lean fi sh has
sometimes been noted to give a less acceptable texture and fl avour. The
role of fats in the fermentation process has not, however, been studied
in any detail. Fish oils are highly unsaturated and hence very prone to
oxidation. Certain pro-oxidants, such as
haem
, in the proteins catalyze the
oxidation reaction. Similarly, iron impurities in the crude solar salt used
for curing also accelerate auto-oxidation (Saisithi, 1967). Oxidized fi sh oils
have a characteristic taste and paint-like smell, but the acceptability of
products having the typical taste and fl avour of oxidized fats depends
very much on local preferences. The products of fat oxidation take part
in further reactions especially with amines (Saisithi, 1967) and with
other decomposition products of proteins (Bal and Dominova, 1967) to
produce coloured compounds as well as substances with odour (Jones,
1966). Lipases present in the fi sh fl esh also hydrolyze the lipids (Lovern,
1962), but the extent is dependent on the level of salting and fermentation
(Amano, 1962; Lee et al., 2008).
Pathogens rarely multiply at high salt concentrations; however, Karnop
(1988) demonstrated that
Pediococcus halophilus
is able to produce histamine
during long storage at ambient temperatures of 20 to 25°C. Toxins
produced by
Clostridium botulinum
in poor quality fi sh before salting may
be stable in the salted product (Huss and Rye-Petterson, 1980).
A study by Knochel and Huss (1984) on the microbiology of barrel
salted herrings revealed that both aerobic and anaerobic viable counts (in
media containing 15% NaCl) were low, i.e. not more than 3 x 105/g of fi sh.
Villar et al. (1985) also showed that
Pediococcus halophilus
is the dominating
organism in salted anchovies. Other halophilic bacteria isolated from
fermented fi sh products were:
Lentibacillus jeotgali
(Korean fermented
seafood) (Jung et al., 2010),
Gracilibacillus thailandensis
and
Salinivibrio
siamensis
(from
Plara
) (Chamroensaksri et al., 2009, 2010),
Piscibacillus
salipiscarius
(from
Plara
) (Tanasupawat et al., 2007). Anihouvi et al. (2007)
studied the microbiological changes in naturally fermented cassava
fi sh (
Pseudotolithus
sp.) for
lanhouin
fermentation. A total of 224 isolates
belonging to the genera
Bacillus
,
Staphylococcus, Micrococcus, Streptococcus,
Corynebacterium
,
Pseudomonas
,
Achromobacte
r and
Alcaligenes
were isolated
from the fermenting fi sh samples.
Lactic acid bacteria (LAB) are also found as the dominant microorganisms
in many fermented fi sh products (Paludan-Muller et al., 2002). The primary
role of LAB is to ferment the available carbohydrates and thereby cause
a decrease in pH. The combination of low pH and organic acids (mainly
lactic acid) is the main preservation factor in fermented fi sh products. In
plaa-som
, major LAB isolated were
Pediococcus pentosaceus
,
Lactobacillus
alimentarius
,
L. planatrum,
L. garviae
and
Weisella confusa
(Paludan-Muller
