Freshly caught miscellaneous fish were transported to the laboratory, gutted and washed before mechanical separation into bone and mince. Seven batches of the mince were then treated with seven different concentrations (Wt/Wt) of sodium chloride before cooking. The cooked mince was divided into two groups, pressed and unpressed. Percentage residual salt of the salted cooked mince, cooked water and salted pressed mince was determined. Also, the moisture content of the salted cooked mince and salted pressed cake was determine

Aliu, A.

Nwanekezie, R.U.

Sorinmade, S.O.

Talabi, S.O.

Aquatic Commons

HIGE TEMPERECURE SALTING OF FISH MIOCE
by
S.O. Talabi, S.O. Sorinmade,
R.U. Nwanekezie and A. Aliu
Nigerian institute for Oceanography
and Marine Research,
(Fish Technology Division)
Victoria Island
Lagos, Nigeria
ABSTRACT
Freshly caught miscellaneous fish were transported to thelaboratory, gutted and washed before mechanical separation into bone
and mince. Seven batches of the mince were then treated with seven
different concentrations (Wt/Wt) of sodium chloride before cooking.
The cooked mince was divided into two groups, pressed and unpressed.
Percentage residual salt of the salted cooked mince,cookpd water
and salted pressed mince was determined. Also, the moisture content
of the salted cooked mince and salted pressed cake was determined.
The moisture corten QS:. both the ,salted cooked mince and salted press
cake decreased with percentage added salt. and an equibirium was
reached around 'i level of added salt,. However, tha moisture content
of the pressed cake was lower than that Og the cooked mince after 10;
level ol added salt. It is interesting to note that the residual
salt in. both the cooked and pressed mn.ce increased with increase
added salt up to 20t where there was en equibirium in the pres6eJ1
mince. Furthermore, there was a direct relationship between percent-
age residual salt in salted cooked mince and-percentage salt in. the
cooked water,
INTRODUCTION
There is an abundant potential of small eized fish species which.
are under-utilized in most parts of the world, the extent of which
is estimated at ove" 6,000,000 metric tonnes, but most of these
fishes are mostly regarded as trash. Because of the need to
increase the protein consumption of the developing countries such
as.Nigeria,it is necessary to examine ways uf utilizing these
so-called trash fish.
Fish is an important nutrient as it is high in Proteins, lipids,
minerals and vitamins. However, these nutrients vary with species.
Because fish deteriorates quite rapidly, unlike meat, it is
necessary to preVent various stages or deterioration so as to make
it available for human consumption. Preservation techniques that
are designed to prevent deteriorative processes include icing,
freezing, canning, drying, smoking and solutes pari.7.icularly salt.
Solutes are used to reduce the water activity of fish tissue.
Scott (1953; 1 955 & 1957),introduced the concept of water activity
as a quantitative approach to the influence of water on microbial
nroliferation in foods. Essentially, the solutes must be compounds
that have good solubility in water and must be able to exhibit very
large negative deviation from Raoulth Law (Benmergui et al, 1979).
Benmergui et al (1979) have also shown that many compounds' including
calcium chloride, magnessuim chloride, calcium iodide, sodium
chloridc, potassium acetate and sodium"formate are all able to
exhibit negative deviations from Raoult Law thereby, depressing
water activity. However, these workers pointed out that no single
electrolyte can provide adequate depressions of water activity when
applied at a level that is organoleptically acceptable.
'132
Inspite of this theoretical consideration, it is to use
'sodium chloride at low levels to inhibit bauterial gro%tb and at
high levels to prevent their growth. Tho mechaniows oZ cha action
of salt as a preservative are more comple7: and thec E,F-Ders to be
a cohflicting understanding of the ?recess rilvole6. ever,
Scott (1957) reported that salt acts by iiering the available
water to micro-organisms. It has been o ved that halphilic
bacteria are able to srrvive high salt cJ-,ntration because they
need sodium chloride to maintain the sta ilitv of their cell walls
(Moht and LorsenT, 1963).
Duer aeld Dver (1952) revealed that the myosim fractions of fish
muscle proteeims were denatured when a criticei salt concentr,ition
of approxlmtely 8 - 10% 71as reached and thFA- ::he -:apid dna,:urn-
tion was acceanle.d by a sudden increase ID salt .reeeke and
moisture lc-,ss. Thus in oractice, it is necessary use levels,
above 1CM salt to lower the water activie c2'f fish as a means of
preservation,
Penetration of fish muscle by salt cannot be over emphasised.
Thus, high temperature has been employed in salting process of fish
mince and muscle because the 'penetration of sodium chloride into ane
the removal of water from fish mince have been found to be faster
(Taylor, 1922; Dyer, 1942; Talabi, 1982). These workers revealed
that the critical salt concentration was reached in a much shorter
time at higher temperatures. Furthermore, Kroemer and Knumbholz
(1931) observed that the maximum salt concentrations in which growtl
occurs is greater at lower temperatures.
Because the underutilized fish are generally throw' eway, we h6 e
attempted in this laboratory to develop a process eeerLey
fish can be fully utilized and made available for en
but the various properties of products from this preeess us Ugh
temperature, salting and pressing have not been elucidated. Thus,
the specific objective of this work was to make a ?preliminary
investigation into the effects of high temperature eelting on the
moisture and residual salt contents of the mechaniceely separated
fish meat in the fully understanding that the amoun of s:,AL
retained by the products and their moisture content can be used to
predict to a large extent the keeping quality of these.producte
MATERIALS AND METHODS
Fresh miscellaneous fish caught off Lagos area coastal water
using Federal Argonaught were Washed with seawater and stored in
ice before transporting to Nigerian Institute for Oceanogrx.hy and
Marine Research (NIOMR)'s processing room. The fish were gutted
and washed before being mechanically deboned using Boader 694
separator. The mince was collected and divided into seven batches
which were mixed thoroughly with different salt levels (0, 5, 10,
15, 20, 25, 30, and 35% wt/wt).
Each batch of salted mince was passed through a cooker/press
system with facilities'for collecting:-
the free at 80°C water produced du2-ing cooking, and
the press water.
The cooked mince was divided into two groups. One group was not
pressed (cooked mince) 'while the other group was pressed into
cakes (salted preseed cake: SPC). Liquid samples were collected
when salted mince was steaming, when it was cooked and the cooked
mince was being expressed and finally when mechanical pressure
was applied to the ,cooked mince. The cooked and pressed mince
were plit in polythene bags, while all water samples were put in
vials and stored in the refrigerator for salt and moisture
analysis.
133
Determination of SodiumChlor de
The salt content of the seated cooked mince (SCM), SPC and cooked
water was determined by a modified A.O.A.C. (1975) silver nitrate
titremetic method.
De ermination of .Moisture Conten
The moisture contents of the SCM and SPC were determined by direct
distillation (A.O.A.C., 1975)-
RESULTS
The effect of varying levels of salt on the moisture content of the
cooked mince and the pressed cake are presented in Figure 1.
Between 0 and 5% added salt, the cooked and pressed cake produced.
did not show much difference in their residual moisture since
approximately the same levels of moisture was observed. At a leVel
of 10% added salt, the residual moisture content of the pressed cake
fell to a. level (70%) that was lower than that of cooked mince
(75.25%). In general, between 0 and 10% added salt, the effect of
salting can be said to be directly related to a gradual,loes of
water with increasing addition of salt to the raw mince. Between
10 and 20% added salt, there was a drastic drop in the residual
moisture level of the cooked mince and pressed cake after which
equilibrium appeared io be attained. It is, however, interesting
to point out that the residual moisture levels in the SPC beyond
the 5% level of added salt were consistently lower than in the cooked
mince. This appears to be due to the effect of pressing and it seems
that the effect appeared to be taking place beyond 15% added salt.
The effects of salting on residual salt in cooked mince and pressed
cake are shown in Figure 2. The variation of added salt with the
residual salt in the cooked mince was up to the level of 20% added
salt. Between 20% and 35% added salt, there was a step-wise
increase in the residual salt content. Almost a linear relationihip
similar to what was observed in the cooked mince was also noticed in
the pressed cake between 0 and 20% added salt. Beyond 20% salt, there
was an equilibrium in the residual salt content of the pressed cake.
The salt levels were consistently lower in the pressed cake than in
cooked mince and the effect of pressing appeared to be fairly
constant until 25% salt was added to the mince. At this point and
beyond, the effect of pressing became significantly pronounced.
The shaded portion in Figure 2 represents the effect of pressing.
While 20% appeared to represent the equilibrium in pressed cake
in respect of residual moisture and salt (Figure 3), the moisture
and salt ecluilibrium in respect of the cooked mince material seemed
to be less-well defined. For instance, the moisture equilibrium
point was 20% whereas, in the salt, two equilibrium points (20% and
30%) appeared to have given rise to the step-wise curve in Figure 2.
The repression curve (Figure 4) shows that there'vas a direct
relationship between residual salt in the cooked mince and the
residual salt in the coOked water.
DISCUSSION AND CONCLUSION
Salt as a preservative has been widely used fer several years.
Unfortunately, with the development of refrigerative technology,
research efforts for food preservation has continued to'decline.
This is even true of the tropical third world countries which can
least afford the luxury of refrigeration. In the preliminary
work of Del Valle and Nickeson (1968), the equilibrium consider-,
ation relevant to fish mince were examined in resPect of ambient
temperature and considerable fundamental knowledge were established
which were later applied in products developtent studies (Bellos
and Pigott, 1979; Young et al, 1979). Salting of fi at room
temperature facilitates an energy efficient removal of water from
fish muscle thereby lowering the water activity and the
susceptibility of such product to microbial damage. Duerr and
134
Deer (1952) observed that salt dema uration point of cod protein
maeleat 10% ane this corresponded to the pointat which high moistureloein began during sa/ting.
There has been o few publicatione =the. application of these
cOncepts by Del Velee et al (1973) at tairly elevated temperature.
The .Most notable oie teese-Tieblications was by Talabi (1981) in
hich meat anel.oguee were suited at high temperture and which
resulted in a reduction ro tri4itearel ambients temperature salting
time when compared to traditional ambient temperature salting.
The approach has now been aduptee to the salting of mechanically
separated fish mince and forms tite basis of this study.
Remelts preuented in rigure 2 clearly ehows that an almost linear
relationship exists between the amount of salt added and the
residual salt that could be obtained when such a mince is subjected
to cooking. The ensuing product les, however, consideeed fairly wet
since it still centains a high moisture content when a high level
of salt (35e) is added (Figure 11. Sueh a material containing a
high level of salt (over 20%) would contain a minimum of 13% salt
as Figure 2 shoWs, However, it is felt in this study that it will
be poseible to remove part of the moisture by a process of preesing
in order to reaere the possibility og the microbial damage. When
preusine was carried out on the coced minces in Figure 2e some
degree of loss of :salt was expereenced and the ehaded protein shows
the effeet of the application of preesing. The technological
significance of pressing is that it enables a reductioe in the
amount of moisture that is available for microbial growth so tbat the
salt level that will be required to prevent such growth will become
considerably reduced. The overview of Figures 1 and 2 i.e. Figure 3,
clearly shows that because equilibrium is attained with pressure at
20%, it seem logieal to suppose that at that level of salt,
increaeing the pressure on the pressing equilibeium may result in a
lower level of moisture. But this was not inveetigated in this
study. It is apparent from this results, however, that the cooked
mince has meximum capacity of ealt and water relation (subject
to the pressing conditione which for the salt wae 11e and for-
Moisture 5%).
Theoretically, this salt level (20e) will still have not saturated
the residual moisture ot 51% and as such, the product may not be
stable to reme microorganisms. It appeared from Figure 3 that
theoretiCal saturation has been achieved only in the cooked mince
at a level above 30% added salt which corresponded to 16.8% salt
and 55t moisture. The theoreticel saturation point of sodium
chloride (salt) used is 26.6% at 20e. This condition allows a
salt aaturation of )0Piii-ehl chloride in water at 20C. Theoretically,
this condition will adequately prevent bacterial growth.
Under the condition prevailing in Lhe f,4quipment used in this
study, it was not possible to produce pressed cake of micro-,
biologically free quality, since it would not be poseible to
saturate the residual moisture in pressed cake with edit. It is,therefore, felt that the pressure may belincreased for improvedproduct.
However, it is posible to produce a microbiologically stable
cooked mince by the addition of a minimum of 30% sodium chlorideprior to cooking. Alternatively, it should be possible by direct
addition of salt eo the pressed cake to increase the salt level
to a level that Will prevent microbiel growth. Further work isbeing contemplated along this direction.
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High temperature salting of fish mince

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