Quality and Safety Assessment of Traditional Smoked Fish from Lagos State, Nigeria  

Adeyeye S. A. O.1 , Oyewole O. B.1 , Obadina A. O.1 , Omemu A. M.2 , Adeniran O. E.1 , Oyedele H. A.1 , Abayomi S. O.1
1. Department of Food Science and Technology, Federal University of Agriculture, Abeokuta, Nigeria
2. Department of Hospitality and Tourism, Federal University of Agriculture, Abeokuta, Nigeria
Author    Correspondence author
International Journal of Aquaculture, 2015, Vol. 5, No. 15   doi: 10.5376/ija.2015.05.0015
Received: 06 Apr., 2015    Accepted: 23 May, 2015    Published: 18 Jun., 2015
© 2015 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Adeyeye S. A. O., Oyewole O. B., Obadina, A. O., Omemu A. M., Adeniran O. E., Oyedele H. A. and Abayomi S. O., 2015, Quality and Safety Assessment of Traditional Smoked fish from Lagos State, Nigeria., International Journal of Aquaculture, 5(15): 1-9 (doi: 10.5376/ija.2015.05.0015)

Abstract

This study was carried out to investigate the quality and safety status of traditional smoked of fish from Lagos State, Nigeria. Fresh fish samples (100) (Silver catfish, Spotted tilapia, Bonga shad, Nigerian tongue sole and Guinea barracuda) were collected from twenty fishing/processing centres from Badagry and Epe Local Government Areas of Lagos State, Nigeria. The samples were divided into two batches, one batch was smoked with drum kiln and the second batch was taken to the laboratory for analysis. Laboratory analyses were carried out on the two batches for: proximate (protein, fat, moisture, crude fibre, and ash), quality indices (peroxide value PV, thiobarbituric acid TBA, total nitrogen base-nitrogen TVB-N, trimethylamine acid TMA, free fatty acid FFA and pH), heavy metals and microbiological (coliform, fuugi, listeria monocytogenes salmonella paratyphi and staphylococcus aureus). The results of the proximate, quality and microbiological analyses revealed that there was significant variations (p<0.05). The mean moisture content of fresh fish samples ranged from 73.48% – 75.94% and that of smoked fish samples ranged from 11.86% - 13.41%. The mean protein content of fresh fish samples ranged from 15.18% – 17.96% and that of smoked fish samples ranged from 54.80% – 59.35%. An inverse relationship was observed between the moisture and protein content in the smoked fish samples. The study showed that smoking affects quality and significantly (P<0.05) reduced the moisture content of smoked fish and the quality indices such as FFA, TBA and PV. The study concluded that the levels of the four heavy metals investigated in the fish samples are generally below the maximum permissible levels set by World Health Organization for Pb (0.3 ppm); Cd (0.2 ppm), Hg (0.2 ppm) and Cr (0.5 ppm) and hence pose no risk to smoked fish consumers. However, samples of smoked fish showed presence of Listeria monocytogenes which may constitute a threat to public health.

Keywords
Fish; Smoking; Quality; Safety; Traditional; Listeria monocytogenes

In most sub-saharan Africa countries, traditional fishing is practiced in almost all rivers, lakes, ponds, and seas (Ahmed, 2011). It represents an important part of total fish captures and is an important sector in the national strategies of fight against poverty, food security and food safety (Ahmed, 2011).They are major source of food for humans providing a significant portion of the protein intake in the diets of a large proportion of the people, particularly so in the developing countries, where it represents about 14% of all animal protein on global basis (Afolabi et al., 1984; Cluca and Ward, 1996, Eyo, 2001, Da Silva, 2002, Abolagba and Melle, 2008). In many Asian countries, over 50 % of the animal protein intake comes from fish, while in Africa, the proportion is 17.5 % (Afolabi et al., 1984; Abolagba and Melle, 2008).
In Nigeria, fish has an edge over meat because it is cheaper and relatively more abundant (Eyo, 2001) and constitutes about 40 % of the animal protein intake (Eyo, 2001; Abolagba and Melle, 2008). Fish is a cheap source of animal protein with little or no religious rejection of it, which gives it an advantage over pork or beef. Fish is a rich source of lysine suitable for supplementing high carbohydrate diet. It is also a valuable source of vitamin A, B and E, iodine and oils containing polyunsaturated fatty acids (Eyo, 2001, Da Silva, 2002, Abolagba and Melle, 2008).
Fish is highly perishable, therefore a considerable effort has been directed to extend the shelf-life of fish using preservation and processing techniques, such as refrigeration, freezing, canning, smoking, salting, and drying. Besides this, some of these techniques can also be used to enhance the value of fish, such as smoked fish. In Nigeria, fish smoking is the most practiced preservation method. Practically all species of fish available in the country can be smoked and it has been estimated that 70-80 percent of the domestic marine and freshwater catch is consumed in smoked form (Akinyemi et al., 2011). Smoked fish constitute a major source of animal protein for a vast majority of the population in Nigeria, particularly the rural population (Eyo, 1992).
The drying effects during smoking, together with the antioxidant and bacteriostatic effects of the smoke, allow smoked products to have extended shelf-life (Eyo, 2001; Hall, 1997). Smoking is commonly applied to fish (Cardinal, et al., 2006; Varlet et al., 2007) and meat products (Poligne, et al., 2002; Modi, et al., 2004) but also to other food categories, such as cheese (Suchanova, et al., 2008) and mushroom (Eissa, et al., 2008).
The typical smoke flavours result from a number of chemicals found in the smoke, but is mostly attributed to the phenols. Phenolic compounds, which are mainly produced by pyrolysis of lignin, are important for preservation and flavour properties of smoked products. The content of phenolic compounds in these products depends on the nature of wood. Phenolic derivatives like guaiacol (2-methoxyphenol) and syringol (2,6- dimethoxyphenol) have been identified as the most characteristic smoke related compounds in smoked fish-like herring (Clupea harengus) (Se’rot, et al., 2004). Guille’n, et al., (2006) analyzed headspace components of cod and swordfish where groups of phenol guaiacol, and syringol compounds derived from wood pyrolysis were most noticeable of the smoke flavor volatiles. In addition to phenolic compounds, furan-like compounds have been reported to be responsible for the smoked odour in smoked salmon while carbonyl compounds, such as heptanal and (E, Z)-2, 6 were characteristic compounds in unsmoked fish, giving the flesh its typical fishy odour (Varlet et al., 2006).
The smoking technique has developed to a point where once common food has become a delicacy and there is need for corresponding concern for safety issues in smoked fish consumption (Riches, 2012). Da Silva et al. (2008) examined the microbial safety and quality of smoked blue catfish (Ictalurus furcatus) steaks treated with antimicrobials and antioxidants during 6 weeks ambient storage. Fafioye et al. (2002) studied the fungal infestation of five traditionally smoked dried freshwater fish in Ago-Iwoye, Nigeria and isolated and identified eleven different fungal species of which Aspergillus flavuswas the most frequently encountered fungi on the fish species. Adebayo-Tayo et al., (2008) reported the presence of aflatoxin and other metabolites in smoked fish due to Aspergilus flavus in smoked fish sold in Uyo, Akwa Ibom State, Nigeria and confirmed that consumers could have been at risk of aflatoxin poison.
This study is to investigate the quality and safety status of traditional smoked fish from Lagos State and by so doing, determine the quality level, heavy metal profile, identify bacteria and fungal species prevalent in traditional smoked fish, their distribution, effects and possible public health implications of the presence of such heavy metals and microorganisms.
1 Materials and Methods
1.1 MATERIALS
1.11 Sample Collection
The fresh and drum kiln smoked fish (Silver catfish, Spotted tilapia, Bonga shad, Nigerian tongue sole and Guinea barracuda) (100) samples were collected from twenty processing centres from Badagry and Epe Local Government Areas of Lagos State, Nigeria.
1.2 Sampling Procedure
The fresh and drum kiln smoked fish (Silver catfish, Spotted tilapia, Bonga shad, Nigerian tongue sole and Guinea barracuda) (100) samples were collected from twenty processing centres from Badagry and Epe Local Government Areas of Lagos State, Nigeria by purposive sampling in sterile containers (Ziploc). Smoked fish samples were taken to the laboratory and analyzed immediately.
1.3 Proximate analysis
The following proximate analyses were carried out on fresh and smoked fish. The moisture content of the fresh and smoked fish were determined by the oven-drying method. Protein contents of the fresh and smoked fish were extracted and fractionated by the method of AOAC (2000) method. The crude fat, crude fibre and ash content of the fresh and smoked fish were determined by AOAC (2000) method.
1.4 Physico-chemical analysis
Kent pH meter (Kent Ind. Measurement Ltd., survey) model 7020 equipped with a glass electrode was used to measure the pH of the flesh, employing 10 g of fish homogenized in 10 ml of distilled water. Triplicate determinations were made in all cases. The pH meter was calibrated using pH 4.0 and pH 7.0 buffers. The total volatile base- nitrogen, trimethylamine value (TMA), thio-barbituric acid value, peroxide value and free fatty acid value of the fresh fish and smoked fish were determined by AOAC (2000) method. All chemicals used in this study were of the analytical grade unless stated otherwise.
1.5 Heavy metal analysis
Heavy metal analysis on fresh fish and smoked fish were determined by AOAC (2000) method using atomic absorption spectrophotometer. All chemicals used in this study were of the analytical grade unless stated otherwise.
1.6 Microbiological Studies
The presence of pathogens in fresh and smoked fish samples were investigated. These include: Listeria monocytogenes, Salmonella paratyphi, Escherichia coli, Staphylococcus aureus and Fungal count. Fish samples (fresh and smoked) obtained from the identified processing centres were analyzed microbiologically. The microbiological procedures recommended in the International Commission on Microbiological Specifi­cation for Foods (ICMSF, 1996) were applied. Culture media were those of Oxoid, Biolife and Difco.For each sample, 25 g were weighed out and transferred to a sterile blender with 225 ml of 0.1% peptone and mixed tho­roughly for 2 minutes to prepare fish homogenate. These were then analysed as follows.
1.6.1 Total viable bacterial counts
Appropriate dilutions of the fish homo­genate were prepared and inoculated onto sterile Petri dishes. Plate count agar (Oxoid) media were then poured. Plates were incubated at 35–37 °C for 48 hours and colonies were then counted and repor­ted as total colony count/ml. A second set of plates was incubated at 35–37 °C for 48 hours in a carbon dioxide incubator or under anaerobic conditions using a gas pack anaerobic jar. Colonies were then counted and reported as anaerobic total bacterial count. In case of spore formers count, the food homogenate was boiled first at 75–80 °C and then rapidly cooled. Ap­propriate serial dilutions were prepared and inocu­lated onto the surface of sterile and dried plate count agar media. These were incu­bated finally at 35–37 °C for 48 hours.
1.6.2 Detection of Escherichia coli
One ml of each of the decimal dilutions of the fresh and smoked fish homogenate was plated on poured Eosine Methylene Blue Agar (Oxoid) and then incubated at 35–37 °C for 24 hours. Counts were calculated from the number of growth on the plates. The colonies with green metallic sheen were counted as Escherichia coli.
1.6.3 Detection of Staphylococcus aureus
A sample of 0.1 ml of the fresh and smoked fish homogenate and dilutions was inoculated on Baird-Parker (Difco) agar plates and incubated at 35–37 °C for 48 hours. Co­lonies appearing to be black and shiny with narrow white margins and surrounded by clear zones were identified by coagulase test reactions. The coagulase test was carried out by first inoculating typical colonies in brain heart infusion broth (Dif­co) and incubating at 37 °C for 24 hours. From the resulting cultures, 0.1 ml was then added to 0.3 ml of rabbit plasma in sterile tubes and incubated at 37 °C for 4 hours. The formation of a distinct clot was evidence of coagulase activity.
1.6.4 Detection of Salmonella paratyphi.
Samples of fresh and smoked fish homogenate and dilutions were inoculated in Salmonella-shigella agar (Oxoid) and incubated at 35–37 °C for 24 hours. For identification, 2–3 suspected colonies were inoculated into tryptone broth for indole test, triple sugar iron agar slant (Oxoid), urea broth and lysine iron agar. These were incubated at 37 °C for 24 hours. Salmonella species is indole nega­tive, on triple sugar iron it produces acid (yellow) and alkaline (red) with or without gas and hydrogen sulfide, is urea negative, and on lysine iron agar shows an alkaline (purple) reaction throughout the medium. Serological tests were then carried out.
1.6.5 Detection of Listeria monocytogenes
A sample of 0.1 ml of the fresh and smoked fish homogenate and dilutions was inoculated on Brilliant Listeria Agar (Oxoid) plates and incubated at 35–37 °C for 24 hours. Co­lonies appearing were counted and reported asListeria monocytogenes.
1.6.6 Enumeration of fungi
Appropriate dilutions of Sabouraud dext­rose agar plates (Oxoid) were poured over 1 ml of the fish homo­genate and dilutions. Plates were incubated at 22–25 °C for 3 days and then colonies were counted and reported as fungal count/ml
1.7 Data Analysis
All data analyses were done in triplicates. The data obtained were subjected to descriptive statistics using IBM SPSS version 21.0 software and Microsoft office excel was used to generate tables and charts. One way analysis of variance (ANOVA) was done using Duncan’s Multiple Range Test (p<0.05) to study the difference between means.
2 Results and Discusion
The mean moisture contents of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 1 and 2) were 74.68%,74.81% , 75.65%, 73.48% and 75.94% and their smoked samples were11.86%, 12.51%, 13.37%, 13.41% and 12.56% respectively. In contrary to protein, fat, and ash, the moisture content of fresh fish samples decreased sharply after the smoking process. There was an inverse relationship between moisture and protein during smoking In the present study, the mean protein contents of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 1 and 2) were 15.70%, 17.85%, 15.18%, 17.96% and 17.89% and their smoked samples were54.80%, 59.35%, 56.18%, 57.11% and 58.63% respectively. The mean fat contents of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 1 and 2) were 8.38%, 5.79%, 7.81%, 6.89% and 4.62% and their smoked samples were19.32%, 13.39%, 18.09%, 12.83% and 14.16% respectively. The mean crude fibre contents of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 1 and 2) were 0.20%, 0.19%, 0.29%, 0.23% and 0.16% and their smoked samples were2.04%, 2.91%, 2.91%, 2.31% and 1.87% respectively. The mean ash contents of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 1 and 2) were 0.13%, 0.15%, 0.15%, 0.11% and 0.13% and their smoked samples were1.34%, 1.52%, 1.46%, 1.13% and 1.12% respectively. The increase in mineral content, ash and crude fibre can be attributed to an increase in the dry matter content per unit weight following sample dehydration and during the smoking process (Da Silva, 2002). Da Silva, 2002 and Da Silva et al., 2008.In this study carbohydrate content was given by difference that is the percentage of water, protein, fat and ash subtracted from 100. The mean carbohydrate contents of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 1 and 2) were 0.91%, 1.21%, 1.33%, 1.07% and 1.16% and their smoked samples were10.64%, 10.32%, 7.99%, 13.21% and 11.66% respectively.


Table 1 Proximate composition of fresh fish samples
 

Table 2 Proximate composition of freshly smoked fish samples

The quality indices of the fresh and smoked fish were studied. The peroxide value (PV) results are similar in pattern to TBA. In this study, PV of fresh
silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 3 and 4) were 6.32, 6.91, 6.11, 7.86and 7.31 mg Eq. peroxide/kg and their smoked samples were9.11, 9.35, 9.05, 9.18and 9.18 mg Eq. peroxide/kg respectively. These values are below the recommended value of between 20 and 40 mg Eq. peroxide/kg for rancid taste to begin. Free fatty acid value (FFA) is the number of mg of potassium hydroxide required to neutralise the free acid in g of the sample. The result is often expressed as percentage of free acidity. The acid value measures the extent to which the glycerides in the oil have been decomposed by lipase action. The decomposition is accelerated by heat and light. As rancidity is usually accompanied by free fatty acid formation, the determination is often used as a general indication of the condition and edibility of oil or oil containing foods. Free fatty acids values (FFA) of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 3 and 4) were 1.16%, 1.21%, 1.03%, 1.07%and 0.94% and their smoked samples were1.21%, 2.17%, 1.13%, 1.41%and 1.34% respectively. These values are very low and below the threshold for rancidity detection in smoked fish. The thiobarbituric acid value (TBA) is used to assess the degree of fish spoilage especially in fatty fish. The TBA test measures a secondary product of lipid oxidation, malonaldehyde (Da Silva, 2002). The TBA values of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 3 and 4) were 0.90, 1.08, 0.96, 0.86 mgMol/kgand 0.89 and their smoked samples were1.10, 1.86, 1.07, 1.19and 1.03 mgMol/kg respectively. The TBA (1.00 to 1.15 mg TBA/kg) did not exceed 1 to 2 mg TBA/kg TVB-N is related to protein breakdown and is an index of fish spoilage (Da Silva, 2002). The legislative standard for TVB-N include: 20 mg N/100g for fresh fish, 30 mg N/100g stale fish and 40 mgN/100g for fish that is unfit for human consumption but can be used for animal feed (FAO, 1992; Da Silva, 2002). In this study, the total volatile base- nitrogen (TVB-N) of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 3 and 4) were 14.63, 14.03, 13.89, 15.3 and 13.67mgN/kg and their smoked samples were19.69, 19.85, 18.33, 19.41and 18.11 mgN/kg respectively. These values are within the range of legislative standard for TVB-N which is 20 mg N/100g for fresh fish. This suggests that the level of protein decomposition or breakdown in all the samples is low. The spoilage of fish is due to bacterial and enzyme action, which results in the production of various volatile compounds such as trimethylamine (TMA), dimethylamine (DMA), ammonia and volatile acids. Trimethylamine (TMA) is a reduction product of trimethylamine oxide during spoilage and ammonia is mainly formed as a product of protein breakdown. Trimethylamine (TMA) is one of the volatile amines plus ammonia which can be used as an index of spoilage (Da Silva, 2002). In this study, the trimethylamine value (TMA)of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 3 and 4) were 2.17, 1.88, 2.42, 2.08 and 2.16 mgN/kg and their smoked samples were2.52 2.33, 2.61, 2.41and 2.38 mgN/kg respectively. The trimethylamine value (TMA) of 1.88 – 2.16mgN/kg for fresh fish samples and 2.33 – 2.61mgN/kg for smoked fish samples are within the range of < 3 mgN/ 100g for fresh fish, > 8 mg N/100G for spoiled fish and > 5 mg N/100g for doubtful quality specified.


Table 3 Quality indices of fresh fish samples
 

Table 4 Quality indices of freshly smoked fish samples

2.1 Heavy Metal Assessments of fresh and smoked fish
2.1.1 Levels of Pb, Cd, Hg and Total Cr in the samples
The results of the mean concentrations of Pb, Cd, Hg and total Cr in the fish samples analyzed are presented in Table 5 and 6. Concentrations of Pb varied from 0.0012 to 0.0018 μg/g in the fresh fish while those of the smoked fish samples varied from 0.0010 – 0.0015 respectively. Among the four heavy metals determined, concentrations of Hg varied from 0.0015 to 0.0023 μg/g in the fresh fish while those of the smoked fish samples varied from 0.0015 – 0.0024 respectively. The Cr concentration ranging from 0.0785 to 0.0998μg/g in fresh fish samples and those of the smoked fish samples varied from 0.0899 – 0.0958, was generally the highest while the Cd level which was found in trace amounts, was the lowest in all the fish samples analyzed. The levels of the four metals recorded for the fish samples in this study are below the values reported by Asegbeloyin et al, 2010; Atunaya et al, 2011; Oluyemi and Olabanji, 2011. Levels of the four heavy metals investigated in the fish samples are generally below the maximum permissible levels set by World Health Organization (Brain and Allen, 1993) for Pb (0.3 ppm); Cd (0.2 ppm), Hg (0.2 ppm) and Cr(0.5 ppm) and hence pose no risk to smoked fish consumers.


Table 5 Heavy metals profile (Concentration (μg/g) of fresh fish samples
 

Table 6 Heavy metals profile (Concentration (μg/g) of freshly smoked fish samples

The study on the absence and presence of pathogens such as Listeria monocytogenes, Salmonella paratyphi, Staphylococcus aureus, and Escherichia coli was conducted to evaluate microbial safety and quality of smoked fish. The results indicated the predominance of Listeria monocytogenes, Staphyloccoccus aureus, Salmonella paratyphi and Escherichia coli in the fresh fish samples. The results of the microbiological study (
Table 7 and 8) indicated that Total Viable Count (TVC) of fresh fish samples increased significantly (p<0.05). Total plate count (TVC) of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Tables 7 and 8) were 7.6 x 108, 9.2 x 108, 8.7 x 108, 7.8 x 108and 8.4 x 106cfu/g and their smoked samples were4.6 x 104, 4.0 x 104, 6.0 x 104, 2.3 x 104 and 5.4 x 104 cfu/g respectively. The TVC values obtained for the smoked silver catfish samples were within the range of specified microbiological limits recommended by ICMSF (1986) for fish and fishery products, the maximum recommended bacterial counts for good quality products (m) is 5 x 105 (5.7 log10 CFU/g). Listeria monocytogenes count of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 7 and 8) were 1.9 x 102, 1.7 x 102, 2.0 x 102, 2.1 x 102and 2.6 x 102 cfu/g and their smoked samples were4.0 x 10, 5.3 x 101, 6.0 x 101, 12.2 x 101and 7.4 x 101 cfu/g respectively. Although the Listeria monocytogenes count values obtained for the smoked silver catfish samples were low, the range of specified microbiological limits recommended by ICMSF (1986) for Listeria monocytogenes for fish and fishery products is the presence of the organism, that is zero tolerance so most of the samples from local drum kiln do not meet the ICMSF recommended microbial specification. Therefore, the smoked fish samples from all processing centres need to be cooked before consumption in order to destroy Listeria monocytogenes that is present in the smoked silver catfish to prevent possibility of food poison by listeriosis. All the smoked silver catfish samples of convention smoke kiln tested negative for Listeria monocytogenes while the fresh fish samples contained L. monocytogenes Goktepe and Moody (1998) reported that Listeria spp. counts of raw catfish fillets were 4.37 log CFU/g; after brining, the count decreased slightly to 3.24 log CFU/g and no Listeria spp. were detected in samples after hot smoking. Staphylococcal count of fresh silver catfish, spotted tilapia, Bonga shad, Nigerian tongue sole, and Guinea barracuda samples (Table 7 and 8) were 5.4 x 102, 4.7 x 102, 8.1 x 102, 7.1 x 102 and 6.3 x 102 cfu/g and their smoked samples were23.4 x 102, 57.3 x 102, 49.0 x 102, 48.0 x 102 and 21.1 x 102 cfu/g respectively. The Staphylococcal count values obtained for the smoked silver catfish were low below the specified recommended value for all fish. The Staphylococcus aureus safety level is equal to or greater than 104/g and in many cases, these levels represent the point at or above which the agency will take legal action to remove products from the market (FDA, 2001). In addition, smoking also reduced Staphylococci, and fungal counts. The isolation of Staphylococcus in smoked samples can be attributed to post processing contamination. Salmonella paratyphi was not detected in smoked silver catfish, spotted tilapia, bonga shad, Nigerian tongue sole, and Guinea barracuda samples and this conformed with the specified microbiological limits recommended by ICMSF (1986) for Salmonella paratyphi count for fish and fishery products which is the presence of the organism, that is zero tolerance. In all cases, this suggests Good Manufacturing Practices (GMP) and no faecal contamination of the products as Salmonella paratyphi and E. coli serve as indicator organisms for faecal contamination of foods.


Table 7 Microbial Quality (cfu/g) and pH of fresh fish samples
 

Table 8 Microbial Quality (cfu/g) and pH of freshly smoked fish samples

3 Conclusion
This study showed that protein, fat, and ash, the moisture content of fresh fish samples decreased sharply after the smoking process. This decrease had been found to be due to loss of water during smoking. It was found that there was an inverse relationship between the moisture and protein content in the smoked fish samples. There was also an increase in mineral content, ash and crude fibre which may be attributed to an increase in the dry matter content per unit weight following sample dehydration. The TBA values were increased in the smoked fish samples. Smoking, however, significantly (p<0.05) reduced the moisture content of smoked fish and the quality indices such as FFA, TBA, PV and total viable count in all samples of smoked fish. The study showed that the levels of the four heavy metals investigated in the smoked fish are generally below the maximum permissible levels set by World Health Organization. Listeria monocytogenes was detected in some smoked fish samples, although at lower levels. However, the presence of Listeria monocytogenes in some samples may pose risk to smoked fish consumers.
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