use of koji and protease in fish sauce fermentation - Agri-Food ...

Singapore J Pri Ind 32: 19-29 2005/06
Sample
number
TABLE 1
COMPOSITION OF MATERIALS FOR PREPARATION OF FISH SAUCE
Fish type Protease (%
of fish weight)
Monitoring of Fermentation Process
A series of chemical tests were carried out to monitor
the fermentation process. A small amount of the
liquid from the fermentation mixture was collected
regularly for chemical analysis. Acidity I, acidity II,
formol-N and total soluble solids tests were carried
out weekly while pH measurements were done
fortnightly. At the end of fermentation, the yield of
fish sauce was determined and analyses of total
nitrogen (Total-N), volatile basic nitrogen (VBN),
sodium chloride and amino acid composition of the
fish sauce were conducted.
The pH was measured by Istek pH meter, Model
725P. Acidity I and Acidity II were determined by the
analytical method for Japanese soy sauce (Okuhara,
1985). The content of amino-type nitrogen were
determined by the Formol-N method (Official Method
of Miso Analysis, 1968). Total soluble solids was
measured by using hand refractometer (Atago, Type
N1 (0 – 32%) and Type N2 (28 – 62%)).
The yield of fish sauce was measured by filtration of
the whole fermentation mixture at the end of the
fermentation period. The weight of liquid obtained
from the filtration would be calculated against the fish
weight. Sodium chloride content measurement was
done by potentiometric titration with 0.1 N silver
nitrate (AOAC, 1980). Total-N was determined by
Kjeldahl method and VBN was determined by
Conway microdiffusion method (Conway, 1950).
Amino acid composition was determined using high
pressure liquid chromatography by the Food and
Nutrition Branch, Veterinary Public Health Division,
Water (% of
fish weight)
22
Koji (% of fishwater
mixture
weight)
Agri-Food and Veterinary Authority of Singapore.
RESULTS AND DISCUSSION
Changes in Chemical Composition during
Fermentation Process
pH, Acidity I
The pH decreased from 5.51 and 5.67 respectively for
hard-tail and round scad at the beginning of
fermentation to 5.15 and 5.06 at the end of
fermentation (Fig 3). Note that in fish sauce
processing, most of the fermentation occurring is
lactic acid fermentation. This was shown further by
the measurement of acidity I, which is correlated with
the amount of lactic acid during fish sauce
fermentation (Fig 4). Acidity I was used to roughly
indicate the adequacy of fermentation, i.e.
fermentation process could cease once the acidity I
reached 10 ml NaOH.
Acidity II, Formol-N
Salt (% of fishwater
mixture
weight)
RS Round scad 1.0 30.0 25.0 16.0
HT Hard-tail 1.0 30.0 25.0 16.0
Acidity II measures the total amino acid level and
formol-N test measures the amino-type nitrogen. As
fermentation progresses, protein is broken down to
amino acids, affecting the flavour of the product. The
greater the amino acid content in the product, the
more flavourful the product will be, though the
overall amino acid composition still plays an
important part in determining overall flavour balance.
As fermentation proceeds, the acidity II and formol-N
values should increase until a certain extent, then
stabilize.