Production of mince from Tilapia using a combination of physical and chemical methods was found to improve the storage life of the mince in the deep freezer. Though the chemical composition of the mince was slightly affected, the mince was microbiologically stable throughout the five weeks frozen storage. Fish cakes prepared traditionally from tilapia minces were more acceptable than oven dried cakes. Production of fish cakes form tilapia will improve utilization of this species in areas where small size tilapia are regarded as fish of low economic valu

Eyo, A.A.

English

Aquatic Commons

STO GE POTEIN TIAL UTILIZATION
OF TILAPIA IWCE
A.A. EY0
National Institute for Freshwater Fisheries Research (NIFFR)
P.M.B. 6006, New Bussa, Nigeria.
ABS'I'RACT
Production of mince from Tilapia using a combination of physical and chemical methods was found to improve the
storage life of the mince in the deep freezer. Though the chemical composition of the mince was slightly affected,
the mince was microbiologically stable throughout the five weeks frozen storage. Fish cakes prepared traditionally
from tilapia minces were more acceptable than oven dried cakes. Production of fish cakes from tilapia will improve
utilization of this species in areas where small size tilapia are regarded as fish of low economic value.
KEY WORDS - Frozen storage, deep freezer, Tilapia mince, filed fish cakes, oven dried fish cakes, acceptability
INTRODIJCTION
The ubiquitous tilapia (Sarotherodon sp,
Oreochromis sp, and Tilapia sp) are important
tropical freshwater fish because of their relative
abundance.. They are wide spread in tropical Africa
contributing about 13 % of the ichthyomas in Kainji
Lake (Ita, 1978), 57% in Lake Volta, 35% in Lake
Kariba (Petr, 1967), and a considerable quantity in
other man-made lakes and rivers. Tilapia have also
gained popularity in tropical fish culture due to
their high fecundity although they have a tendency
to overpopulate the ponds. This behaviour has led
to the production of small size Tilapia which
mature when still small (Lowe, 1955) and may
reduce yield and size of the fish at harvest
(Hickling, 1960).
In Nigeria, stunted tilapia when harvested are often
discarded because they fail to command a good
market price; their small size is not easily accepted
by consumers. With the shortfall in fish supply and
the rising cost of other animal protein sources, such
tilapia could supply the much needed protein if
th.ey are reintroduced into the human food chain.
The production of mince from tilapia could be a
valuable source of utilizing unacceptable tilapia for
the production of a versatile protein rich product.
Fish mince is flesh separated in a communited
form from the skin, bones, scales and fins of fish
(Grantham, 1981). Production of mince from
135
underutilized and unused species is not only an
efficient way of recovering flesh for direct use as
human food, but also a vvide range of by-products
such as pet foods and livestock meal can be made
from the bones as well as the scales, liver, swim
bladder etc. (Allsop, 1974).
Considerable research into ways of utilizing the
unused fish products have been extensively
conducted by various workers (Young et al, 1979,
Poulter and Trevino, 1983; Poulter and Poulter,
1984) although less work has been done on raince
from Tropical and Sub-tropical species (Grantham,
op. cit). However, spice minced fish have been
produced in Malaysia from Tilapia (Zain, 1980)
and locally from by-catch (Akande, 1991). Thus,
increased utilization of tilapia could be achieved if
a variety of products acceptable to the local
consumers are made from these species. This paper
describes the production of fish cakes of acceptable
quality from tilapia mince.
MAMMALS AND METHODS
Raw materials: Tilapia (Oreochromis
niloticus) purchased fresh from fishermen and
stored in a deep freezer for approximately 24
hours before use.
Preparation of fish: The frozen fish were
allowed to thaw in air at room temperature,
scaled, headed, g,utted and washed thoroughly
in tap water before they were cut uto small
pie,ces of about 1 cm.
Deboning: Mince was separated front the
bones by a combined chemical ami physical
methods as reported by Gelman, Benjamin
and Herzberg (1983).
Dewatering: The 'minced fish i,vas filtered
thorough approximately 1 nun mesh cloth.
Sufficient pressure was applied to squeeze out
excess water until solid fragments started
passing duough the cloth. The mince vas
weighed.
Storage: The minced fi.sh pre,pared at weekly
intervals was stored in a deep ,freezer
operating at a temperature not below -
for a maximum of five weeks during which
time chemical analysis and bacterial counts
were carried out at weekly intervals.
Analytical Mfethods
Chemical composition:- All samples were
determined in triplicates. Crude protein, lipid,
moisture and mineral contents were determined
according to the AOAC (1990) methods of
chemical analysis. Free :fatty acid was determined
according to Pearson (1976). pH was determined
using pH meter. The Total Volatile Nitrogen
(TVN) was determined according to the method of
Lucke and Geidel (1935).
Total Viable Count (TVC)
The standard pour plate method vas used for the
TVC. The nutrient agar and relevant glass wares
were autoclaved at 121 °C for 15 minutes. 1 gin
sample was homogenised for 2 minutes in 50 cm'
distilled water. Serial dilution of the homogenate
was carried out and 1 cm3 of diluent 1,vas poured
on the sterilized petri dishes. Nutrient agar was
poured oil the diluent in the petri dishes and after
thorough mixing, the petri dishes were incubated at
35°C for 48 hours and the organisms counted in
colonies using colony Owner.
Preparation of fish Cakes
The minces of different storage periods were mixed
with potato mash in the ratio of 1:1. Onions and
spices were added to improve the product flavour.
Rectangular cakes of approximately 50 gm weight
were formed from time mixture using tin. moulds.
136
The cakes were separated into two groups *A'and
'13' made of cakes of storage period of one to five
1,veeks. Cakes in group 'A' were fried in hot
vegetable oil, while those in group '13' 1,yere oven
dried.
Organoleptic Assessment
A total of 10 assessors were randomly drawn from
the staff of the Institute for the organoleptic
assessment. A questiormaire for the assessors was
modified from that earlier used (Eyo, 1985) A ten
point hedonie scale was used. 1 - 3 points cakes
not accepted, 4-5 points fairly acceptable, 6-8
points acceptable and 9-10 points excellent.
Statistical Analysis
The correlation coefficient was employed for the
statistical evaluation of taste panel scores for
acceptability of fish cakes.
RESULTS AND DISCUSSION
Chemical Composition
Table 1 shows the chemical composition and total
viable count of stored minced Tilapia. The cmde
protein level of the mince was 14.93% and this
was lower than that of the fresh sample, 18.10%.
Poulter and Trevino (1982) had similarly observed
lower total crude protein values in minces prepared
with acetic acid compared with manually prepared
mince. There was also minimal changes in the
crude protein content from 14.93 - 14.27% during
the five weeks frozen storage of the mince.
Similarly, Joseph and Perigreen (1983) reported
slight changes in the crude protein, level of frozen
stored minced fish from threadfin bream.
The, lipid content of the mince was quite low
0.40% Which 1,vas attributed to the use of acetic
acid for the preparation of the mince which has
been found to degrade fat containing tissues
(Grimtham op. ea), while subsequent washing of
the mince was found to remove a considerable
amount of fat (Sidewell, 1980). The decrease in the
lipid content during frozen storage was followed by
ami increase in the Free Fatty Acid which
determines the extent of lipolysis (Figure I), Since
fat degradation has been identified as a major
problem in minces ftom both fatty and low fat
species (Grantham, 1981) and the Free Fatty Acid
calculated as Oleic acid were less than 0.5% (a
A13
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Table 1 - Chemical composition and total viable count of tilapia mince
138
Sample
Storage period (weeks)
2 3 4 5
Crude protein (% mince) 14.93 14.56 14.56 14.37 14.27
Lipid content (% mince) 0.89 0.68 0.85 0.85 0.83
Moisture (% mince) 68.10 68.12 67.20 67.40 67.60
Mineral content ( %mince) 7.12 7.14 6.88 7.60 7.21
Calcium (% mince) 1.32 1.48 1.32 1.50 1.48
Pottasimn (%) 0.32 0.40 0.33 0.24 0.33
Iron (ppm mince) 1.06 1.30 1.28 1.36 1.38
Sodium (% mince) 0.33 0.35 0.28 0.41 0.44
pH 6.50 6.70 6.75 6.80 6.80
Total viable counter (TVC) organisms/g. 58 58 70 80 98
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minimum level by which the acidic flavour
becomes noticeable (Pearson, 1976), it is protable
that the mince was stable from excessive fat
decomposition during the five weeks frozen
storage. The use of antioxidants for fat stabilization
of tilapia raince stored for five weeks in the deep
freezer was considered unnecessary. There were
slight variations in the moisture and mineral
contents of the mince during storage though, these
were insignificant. Considerable variations among
minerals during storage was noticeable which could
have been caused by leaching of the minerals
during the dewatering and washing stages. The pH
was near uniform throughout the storage of the
mince
Total Volatile Nitrogen (T'VN)
TVN is related to protein breakdown and is widely
used as an index of fish spoilage (Chakrabarti,
1984). The gradual increase in the TVN content of
the raince was accompanied by a decrease in its
crude protein content (Figure 2). The TVN content
of 17.5 mg N/100 g mince after five weeks frozen
storage was less than the 20 mg N/100 g limit for
freshness of white fish using the Lucke and Geidel
method (Pearson, 1976). Therefore, the mince was
free from deterioration during the period of frozen
storage. This observation was further supported by
results of organoleptic assessment of cakes
prepared from the raince (Table 2).
Microbial Content
Low microbial count was noticeable during the
period of frozen storage. The count ranged from 55
to 98 organisms/g during the five weeks storage
and was less than that obtained by Young and
Romero (1979) using a Paoli model 19 authomatic
meat bone separator (180 organisms/g). The use of
acetic acid and the low pH during the preparation
of the mince produced an unfavourable condition
for microbial growth. Subsequent low moisture
level in the raince and the inhibitory effect of low
temperature storage may have produced adverse
conditions for microbial build up in the mince
Yield
The minced Tilapia was dewatered to a final
weight of 30-35% of the wet weight of the fish.
Young et al (1979) reported yield of 35-40% for
shrimp by catch, while Gelman et al (1985)
obtained a yield of 42-45% of the weight of whole
140
small pelagic fish from Israel. The yield of mince
is affected by such factors as types and sizes of
fish and method of mince production.
ORGANOLEPTIC ASSESSMENT
OF FISH CAKES
Table 2 shows the result obtained from the
assessors using ten points on the hedonic scale. All
the ten assessors, found all the products to be
acceptable for all the parameters tested.
Colour
There was a significant difference (P <0.01) when
the oven dried and :hied cakes were compared with
the assessors showing preference for the colour of
the fried cakes. This was attributed to the brownish
discolouration of the fish cakes which was more
attractive than the pale white appearance of the
oven dried cakes. On testing the colour against
storage period, no significant difference was
observed (P> 0.01) inidicating that prolonged
storage of the mince in the deep freezer had no
effect on the appearance of the cakes.
Texture
The assessors did not observe any significant
difference in the texture of the fried and oven dried
cakes (P > 0.01) nor in the cakes prepared from
rainces after frozen storage.
Taste
A large preference which was statistically
significant (P <0.01) was given to the taste of the
fried cakes. When the taste of the cakes prepared
from one to five weeks old samples were
compared, assessors noticed changes in the taste of
these cakes. Preference was given to cakes prepared
from minces that were of less than 4 weeks frozen
storage. There was however, no rejection of other
cakes. Thus, prolonged storage of mince in the
deep freezer affected the taste of the cakes which
was noticeable by the assessors.
CONCLUSION
Production of traditionally acceptable fish cakes on
a commercial scale from small size tilapia will go
a long way in improving revenue of the fish farmer
in places where small size tilapia are regarded as
fish of low economic value.
20
Storage in weeks
Figure 2: Changes in Crude Protein ( ----) and Total Volatile Nitrogen (
of Tilapia mince During Storage in the Deep Freezer.
141
Plate 1: Samples of fish cakes prepared from Tilapia mince, Sample A: fried in oil;
Sample Et Oven dried.
142
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A.O.A.C. (1990) Association of official analytica/ Chemists.
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1298 pp.
Akande, G.A. (1991). Production of commercially profitable
spiced minced fish cakes from byecatch. Proc. Fourth,
Ann. Seminar CODRI Lagos 102-110.
Allsop, W.H.L. (1974) Research and development activities of
International Development Research Centre of Canada in
West Africa and the Caribbean. In: Kreuzer, R. Fishery
Products. West Byfleet, Surrey, England. Fishing News
(Books) Ltd. 44 - 445.
Chakraharti, R. (1984). Changes in the musc/e of three Indian
major carps during frozen storage. Fishery Technology
21, (2):91- 93.
Eyo, A.A. (198$) Evaluation of the colour and flavour of tilapia
smoked with different wood types. Tropical Science 25:
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Gelman, A. Benjamin, E and Herzberg E.(1985) Production
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Grantham, C.J. (1981) Minced fish technology: A review.
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Storage potential and utilization of tilapia mince

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Storage potential and utilization of tilapia mince

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