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Research Article
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Effect of Post-slaughter Time Intervals on the Quality of the African Catfish, Clarias gariepinus (Burchell, 1822) |
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A.A. Ayeloja,
F.O.A. George,
S.O. Obasa
and
L.O. Sanni
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ABSTRACT
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Effect of post-slaughter time intervals on the quality of fresh and hot smoke-processed African catfish, Clarias gariepinus products was investigated. A total of one hundred and four live catfish (average weight 700.0±7.0 g) was slaughtered and smoked. Ten freshly slaughtered fish samples were selected for organoleptic assessment at 0, 4, 8 and 12 h post-slaughter respectively. Three fresh and smoked fish samples each were selected for chemical and microbial analyses using standard analytical procedures. Microbial load on both fresh and smoked fish samples increased significantly (p<0.05) with increase in post-slaughter time interval (PSI) with lowest value of 5.52±0.03 and highest value of 5.87±0.03 Log Cfu g-1 for fresh fish samples and lowest and highest values of 2.04±0.02 and 3.09±0.10 Log Cfu g-1 respectively for smoked fish samples. Bacteria isolates identified from fresh samples included: Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Bacillus spp and Staphylococcus aureus; while E. coli, S. aureus and Bacillus spp. were isolated from smoked fish samples. Protein and ash contents of fresh fish samples increased progressively with increasing PSI while moisture content decreased; and lipid content remained unchanged. Protein, lipid and ash contents of smoked C. gariepinus significantly (p<0.05) decreased with increased PSI while moisture content increased significantly (p<0.05) with increasing PSI. This study suggests that C. gariepinus should be smoked immediately after slaughter for best quality hot-smoked fish products.
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Received: February 22, 2011;
Accepted: April 13, 2011;
Published: May 21, 2011
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INTRODUCTION
Fishery resources are important sources of dietary protein in most coastal
communities in Nigeria and the world at large (Widjaja et
al., 2009). Fish supplies a good balance of protein, vitamins and minerals
with very low carbohydrate content; hence its role in nutrition is recognized.
Research confirms that fish is a rich source of essential nutrients required
to supplement both infant and adult human diets (Abdullahi
et al., 2001; Adeparusi et al., 2003).
In spite of the importance of fish in human nutrition and health, an estimated
40% of total fish landing in Nigeria is lost as post harvest losses. Eyo
(2001) estimated that 20 to 50% of the fish produced in the remote coastal
centers and hinter land of many tropical countries perish before they reach
consumers due to the poor handling, preservation and processing practices adopted
by the artisanal fishermen, fish farmers and fisheries entrepreneurs. In addition,
significant quality is lost through the absence of adequate technology and know-how
to prevent losses in many tropical countries. According to Clucas
(1990), the rate of fish spoilage depends on handling during processing,
acidity level, species of fish, weather conditions, mode of storage and temperature
during transportation while Daramola et al. (2007)
reported that chemical breakdown of protein, fat and water contents contribute
to rapid spoilage of fish. Hood et al. (1983)
also reported that microbial load increases with increasing temperature and
results in rapid fish spoilage while Bernacsek (1993)
noted that variations in product quality arise from differences in the freshness
of the raw material and preparation of fish prior to smoking.
A number of processing techniques are in operation in Nigeria, these include:
chilling, freezing, salting, canning, drying and smoking (Kumolu-Johnson
et al., 2010), however, smoking is the most popular method of fish
processing (Bako, 2005). Fish smoking is particularly
relevant in the artisanal fisheries sector in that it prolongs the shelf-life
of the fish, enhances flavour and increases utilization of the fish in addition
to reducing wastes when catches are good as well as increasing protein availability
to rural people (Jallow, 1995).
Clarias gariepinus is a very important fresh water fish in Nigeria (Idodo-Umeh,
2003) and enjoys wide acceptability in most parts of the country because
of its unique taste, flavour and texture. It is widely distributed and extensively
cultivated in ponds, but is still undervalued. This informs the choice of Clarias
gariepinus for the present study. Akande and Ola (1992)
observed that a 3 h post-slaughter holding of fish at ambient temperatures prior
to processing still resulted in good quality hot-smoked fish products; thus
it is not necessary to keep the fish for less than 3 h post-slaughter at ambient
temperatures for this study. This study was carried out to assess the effect
of post-slaughter time intervals on organoleptic, microbial, and chemical characteristics
of raw and smoke-processed C. gariepinus, with an overall objective of
determining appropriate post-slaughter time interval suitable for the production
of good quality smoke-dried products of C. gariepinus.
MATERIALS AND METHODS
One hundred and four live C. gariepinus of approximately five months
of age and average weight of 700.0±7.0 g were collected early in the
morning from concrete tank of Palm Royale Foods fish farm at Odogunyan, Ikorodu,
Lagos State, Nigeria. The size of the culture tank was 8mx7mx7 m and the water
temperature at the time of collection was 27±2°C. Thereafter, the
fish were transferred by road within 90 min to the Nigeria Institute for Oceanography
and Marine Research (NIOMR) laboratories using eleven 30 L capacity plastic
bowls with < 10 fish in each bowl. The fish were later kept in a holding
tank (7mx7mx6m) for twenty-four hours. The water temperature in holding tank
at the time of storage was 27°C±2. Fifty-two fish were randomly selected,
stunned by a hard hit on individual fish head and slaughtered using a sharp
knife, washed with clean portable water and allowed to drip. Fish were later
spread in the laboratory at ambient temperature (27°C±2). Twelve
samples from the slaughtered C. gariepinus were filleted immediately
to determine their proximate composition and microbial load, while forty samples
(ten at different time intervals of 0, 4, 8 and 12 h, respectively) were collected
for organoleptic assessment. Fifty-two samples of C. gariepinus were
selected for smoking, with 13 samples each slaughtered at four time intervals
ranging from 0 h (immediately after slaughter), 4, 8 and 12 h post-slaughter.
Immediately after the fish were slaughtered for each treatment, they were immersed
in 8% brine prior to smoking.
Nigerian Institute for Oceanography and Marine Research (NIOMR) smoking kiln
was used at a temperature of 35±10°C for the first two hours and
then at 100±10°C for another four hours, totaling 6 h (Obileye
and Spinelli, 1978; Horner, 1997). Charcoal and Anogeissus
leiocarpa were used to generate heat and smoke. A. leiocarpa was
used because it is a hardwood believed to generate smoke with greater preservative
potential than smoke from soft wood (Eyo, 2001). After
smoking, three samples each were randomly selected from each treatment for the
determination of proximate composition and microbial load, while the remaining
ten samples for each treatment were used for organoleptic assessment. This study
was carried out between March and August, 2008.
Proximate analysis: Crude protein, moisture, ash and fat contents of
the fresh and smoked fish were carried out in triplicate in accordance with
the AOAC (1995). The protein content was obtained through
the determination of total nitrogen by micro Kjeldahls method and the
value of nitrogen obtained was multiplied by 6.25 to obtain the crude protein
value.
Moisture content of samples was determined in accordance with AOAC
(1995). The fat content was determined by extraction with petroleum ether
by soxhlets method.
Microbiological analysis: Total viable microbial count was determined
using routine microbiological procedures described by Olutiola
et al. (1991) and Fawole and Osho (2002) and
identified using Bergeys Manual of Determinative Bacteriology.
Organoleptic (sensory) assessment: Sensory evaluation was carried out
by a ten-man trained panel from NIOMR using a 5-point hedonic scale modified
from Eyo (2001) and Tobor (1985).
The following grades were allotted depending on the condition of the fish:
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8≤10 |
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Very good |
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6≤8 |
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Good |
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4≤6 |
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Fair |
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2≤4 |
= |
Bad |
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≤2 |
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Very bad/unacceptable |
Eyes, gills, skin, odour and flesh were examined for raw samples; while odour,
flavour and texture were examined for smoked samples using the five-point hedonic
scale.
Statistical analysis: Analysis of variance (ANOVA) was carried out using
F-test to determine the treatments level of significance and treatment
means were separated using Duncan Multiple Range Test (DMRT) at 95% confidence
value i.e., (p<0.05).
RESULTS AND DISCUSSION
The results of the microbiological study (Table 1) indicated
that Total Viable Count (TVC) of fresh fish samples at 0 h interval recorded
the lowest TVC of 3.37x105 (Cfu g-1) and TVC value increased
significantly (p<0.05) up till 12 h post slaughter. This is in accordance
with the report of Hood et al. (1983) and Colakoglu
et al. (2006) that microbial load increases with handling, duration
of storage and temperature. This study established that fish left at ambient
up to 8 hours post-slaughter still had TVC values within the maximum recommended
bacterial count for good quality fish product which is 5x105 (5.7
log10 Cfu g-1) according to the International Commission
on Microbiology Safety for Foods (ICMSF, 1986).
Table 1: |
Total microbial count of raw and cooked C. gariepinus |
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Means with different superscripts in the same column indicate
significant difference at p<0.05 |
Table 2: |
Bacterial isolates from raw and smoked fish samples |
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+: Presence, - : Absence |
This value was however exceeded in fresh fish samples left at ambient temperature
for 12 h post slaughter with the value of 7.31x105 of 5.869 log10
(Cfu g-1), yet the fish was not totally unacceptable as it has not
exceeded the maximum recommended bacterial counts for marginally acceptable
products which is 107 (7log10 Cfu g-1) (ICMSF,
1986). Microbial quality evaluation confirms the presence of various psychrophylic
microorganisms indicated in fish spoilage (Oksuztepe and
Inanli, 2007) including Klebsiella pneumoniae, Staphylococcus
aureus, Pseudomonas aeruginosa and Bacillus spp. This study
also establishes that smoking reduces TVC in C. gariepinus with a lower
value of 1.10x105 (Cfu g-1) recorded for fish smoked immediately
after slaughter and values increasing significantly (p<0.05) at successive
four hours of 4, 8 and 12 post-slaughter. The highest TVC which is 1.24x103
obtained from C. gariepinus smoked at 12 h post-slaughter interval was
still below the minimum recommended bacterial counts for good quality fish products.
This means that C. gariepinus still gives good quality products if held
for up to 12 h after slaughter prior to smoking.
Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus,
Pseudomonas aeruginosa and Bacillus spp. where isolated from fresh
fish samples (Table 2) while only Escherichia coli, Staphylococcus
aureus and Bacillus spp were isolated in the smoked fish products
(Table 2). This conforms to the report of Fernandez
et al. (1998) that heat treatment during hot smoking of fish would
destroy or inactivate most of pathogens found in fish.
Table 3 presents the proximate composition of fresh and hot-smoked
C. gariepinus. The highest moisture content (78.32±0.50%) was
recorded in freshly slaughtered C. gariepinus (0 h) with values decreasing
significantly (p<0.05) with increase in post slaughter intervals. However,
the lowest moisture value of 44.88±0.61% was recorded for fish smoked
immediately after slaughter with values increasing significantly (p<0.05)
with increase in post-slaughter intervals. The observed loss of moisture after
smoking was due to moisture reduction through heat application during hot smoking
(Kumolu-Johnson et al., 2010) and is in agreement
with the findings of Salan et al. (2006) and
Kumolu-Johnson and Ndimele (2001) that spoilage of fish
resulting from the action of enzymes and bacteria can be slowed down by the
addition of salt as well as reduction in moisture through sun drying or smoking.
Table 4: |
Mean sensory score for raw and smoked Clarias gariepinus |
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Mean±SD with different superscript in the same column
indicates significant difference at p<0.05 |
The percentage protein contents of fresh fish samples increased significantly
(p<0.05) with increase in post slaughter interval, while it decreased significantly
(p<0.05) with increased post slaughter intervals for smoked samples. This
was probably due to moisture loss and an increase in dry matter content per
unit of fish weight following sample dehydration (Omojowo
et al., 2009). Results in the present study reveal that C. gariepinus
has similar ash contents between 0 and 4 h post-slaughter, followed by 8 and
12 h post-slaughter. It was observed that the ash content of the smoked fish
decreased significantly (p<0.05) from 0 to 12 h post slaughter. Hours of
delay after slaughter however, had no significant (p<0.05) effect on the
lipid of fresh C. gariepinus, however, percentage lipid contents of the
smoked fish samples significantly (p<0.05) decreased with increases in post
slaughter intervals. It was observed that lipid content of smoked fish was higher
than the values of fresh fish samples. This agrees with the view of Doe
and Olley (1983) and Huda et al. (2010) that
fish processing often results in the concentration of nutrients like crude protein
and fat and that the quality of fish products is influenced by fish species
differences, processing (including smoking), storage practices and duration
of storage (Widjaja et al., 2009; Kayim
and Can, 2010). In general, the proximate composition and chemical quality
of experimental fish reduced as post-slaughter interval prior to smoking increased
in agreement with Ahmed et al. (2010).
Table 4 shows the mean sensory scores for fresh and smoked
C. gariepinus. There was a significant (p<0.05) effect of post slaughter
interval on the sensory quality of fresh and hot-smoked C. gariepinus.
C. gariepinus retained most of its original freshness up to 4 h post
slaughter, with the eyes transparent, clear and protruding with white cornea
and dark pupil; the gills retaining a bright red colour and fresh odour, the
skin bright, shinning with slime and a firm belly. The flesh remained firm,
flexible and elastic while the odour was fresh and sea weedy. This result agrees
with the findings of Akande and Ola (1992) that African
catfish Clarias gariepinus retained most of its original freshness up
to 3 h post-slaughter. Similarly, the fish smoked immediately after slaughter
(0 h) displayed very good physical attributes, with a fresh sea weedy, fishy
odour and delicious flavour and sweet taste while the texture was firm and tender.
Akande and Faturoti (2003) reported similar results
for Bonga (Ethmolosa fimbriata). Fish delayed for 4 h before smoking
had good fishy odour, sweet flavour and slightly firm texture. However, C.
gariepinus started losing its physical attributes when delayed for over
8 h after slaughter before smoke-processing. Similar findings were reported
by Akande and Ola (1992) that deterioration was rapid
in Clarias gariepinus delayed for 7 and 9 h and left at ambient temperature
after slaughter prior to smoking. Fish smoked after being delayed for 8 and
12 h post-slaughter still displayed good physical attributes. The odour was
fair, not offensive, the texture and flavour were good and the fish still had
a sweet flavour and slightly firm texture. This agrees with the report of Sveindsdottir
(2006) that smoke compounds play a dominant role in colour development as
they cause the reactions of the Maillard type. Maga and
Chen (1985) also reported that smoke contributes to overall smoky aroma
of fish. This study also agrees with the report of Bernacsek
(1993) that variations in product quality stem from the differences in the
freshness of the raw material and the preparation of the fish prior to smoking.
CONCLUSION
This study confirms that fish quality deteriorates progressively with increasing
post slaughter interval and hot smoking of fish inactivates and destroys pathogens
normally associated with unprocessed fish. The study also confirms that fresh
fish quality was still within acceptable limits when fresh fish is held up to
12 h post-slaughter at ambient temperatures before processing. However, delaying
fresh C. gariepinus beyond 12 h post slaughter at ambient temperatures
prior to smoke-processing should be avoided as the quality of the resulting
product is reduced with total viable bacterial count in excess of the recommended
level of 5x105 (5.7 log10 Cfu g-1) for good
quality product. Smoking in this study reduced the incidence of micro-organisms,
hence guaranteeing the safety of the product. For premium quality hot-smoked
products, C. gariepinus should be smoked immediately after slaughter.
ACKNOWLEDGMENT
The authors are grateful to Dr. G.R. Akande and the entire management and staff
of Nigeria Institute for Oceanography and Marine Research (NIOMR), Lagos for
providing necessary facilities and valuable suggestions during this study.
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