2. Materials and methods
2.1. Plasom preparation
The original formula of Plasomconsists of 1 kg fi sh(Oreochromis
niloticus), 10 0 g table salt and 20 0 g sugar. The mixtures were
transferred to a bucket and covered with polyethylene fi lm. The
containers were incubated at room temperature (30 2
C) for 8
days ( Fig.1). During fermentation, each bucket was taken for LAB
isolation every two days. Prior to isolation the selected sample was
blended and used as a composite sample.
Plasom production processing
Raw material
Fish
Size selected and Cut
Washed
Fish+Ingredients
Fermentation
Mixed with roasted rice
Packed
Distribution
Ingredients
(Salt + Sugar and Roasted rice)
Fig. 1. Plasomproduction processing. Hwanhlem et al.
2.2. Isolation of L AB
Twenty- five grams of the sample were added to 225 ml of sterile
0.05 M potassium phosphate buffer pH 7.2 containing 1% NaCl (PBS)
and shaken for 5 min. Appropriate decimal dilutions were prepared
in PBS buffer and poured into a sterile petri dish on de Man Rogosa
and Sharpe (MRS, Labscan Asia Co., Ltd., Thailand) agar containing
0.3% (w/v) CaCO
3
(Maragkoudakis et al., 20 0 6). This was subjected
to incubation at 37
C for 24 h. Bacterial colonies that exhibited
clear zone on the plates were individually picked and streaked on
MRS agar containing 0.3% (w/v) CaCO3
. This procedure was
repeated in order to purify the isolates. Each of the isolates was fi rst
tested for catalase by placing a drop of 3% hydrogen peroxide
solution on the cells. Immediate formation of bubbles indicated the
presence of catalase in the cells. Only those isolates which were
catalase negative were Gram-stained, and only those which were
Gram-positive were maintained in MRS broth containing 25%
glycerol at 20
C. For routine analysis, strains were subcultured
twice in MRS broth for 24 h at 37
C. Selected LAB were identifi ed
by 16S rDNA analysis.