Biology Reference
In-Depth Information
et al., 2002), 42% isolated strains were
P. pentosaceus
. In
som-fak
(a Thai low-
salt fermented fi sh product), a succession of aciduric, homo-fermentative
lactobacillus species, dominated by
Lactobacillus plantarum, L. pentosus,
Lactococcus lactis, Leuconostoc citreum
was found during fermentation
(Paludan-Muller et al., 1999). Further, at the start of fermentation,
Leuconostoc
spp.,
Leuconostoc lactis
subsp.
lactis
and
Lactobacillus brevis
were dominant, followed by more acid tolerant species of
L. planatrum
, the
latter dominating the LAB microfl ora towards the end of fermentation.
Biochemistry
General Studies
Several studies have been carried out to study the biochemical pathways
followed during the degradation process of fi sh fermentation. Pearson
(1970) identifi ed the following fi ve chemical changes in deteriorating
fi sh:
• Enzymic degradation of nucleotides and nucleosides in the fl esh
leading to the formation of inosine, hypoxanthine, ribose, etc.
• Bacterial reduction of trimethylamine oxide (TMAO), a non-volatile
and non-odouriferous compound, to volatile trimethylamine (TMA)
which has an amoniacal smell
• Formation of dimethylamine (DMA)
• Breakdown of protein with subsequent formation of ammonia (NH
3
)
indole, hydrogen sulphide, etc.
• Oxidative rancidity of the fat.
In the degradative changes occurring during fermentation no signifi cant
changes were observed in the amino acids particularly the essential ones.
The degradation process, however, brings out certain characteristic
fl avours which are essential for the quality of the fi nal product.
Hiltz et al. (1976) reported that the volatile bases particularly TMA,
DMA and NH
3
, are associated with changes in the organoleptic and
textural quality of fi sh. The development of a specifi c aroma in fermented
fi sh sauces and pastes may not be due to the action of microorganisms.
Adams (1986) advocated that microorganisms play little or no part in
aroma production. Beddows (1985) isolated halotolerant organisms,
Bacillus
spp. and used them in pure culture but none of them produced
the typical fi sh sauce aroma.
Biochemistry of Fish Sauce and Paste
Amino acids are considered the major contributors to the taste of fi sh sauce
(Lopetcharat et al., 2001). The fl avour and aroma of fi sh sauce is thought to
arise in part from glutamic acid, histidine and proline (Saisithi et al., 1996;
Raksakulthai and Haard, 1992). For example, glutamic acid and lysine were
