Nutrition and Food Technology-Sci Forschen

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Contaminations in Wild and Farmed Fish and Influence of Traditional Cooking Methods

  Samar Aref1*      Noha Morsy2      Ramadan A Habiba1      Mohamed Abdel-Daim3      Fatma Zayet1   

1Department of Food Science & Technology, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt
2Department of Food Science & Technology (Home Economics), Faculty of Agriculture, Suez Canal University, Ismailia, Egypt
3Department of Pharmacology, Faculty of Veterinary Medicine, Suez Canal University, Ismailia, Egypt

*Corresponding author: Samar Aref, Department of Food Science & Technology, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt, Tel: 00201008522305; E-mail:


Due to the increasing concern of consumers about farmed fish contamination, in this study, different wild and farmed fish species (Nile tilapia (Oreochromis niloticus), gray mullet (Mugil cephalus), and thin lip gray mullet (Liza ramada) commonly consumed in Egypt, were chemically analyzed for the presence of heavy metals, antibiotics, polycyclic aromatic hydrocarbons, organochlorine pesticides residues, hormones and microbiologically evaluated for total counts of aerobic and coliform bacteria. Moreover, the influence of traditional cooking methods (i.e., grilling, frying, and baking) on these parameters were estimated. The results revealed that the polycyclic aromatic hydrocarbons and hormones were not detected in the fish species. However, heavy metals; cadmium, lead, nickel, cobalt, zinc, and mercury) were found in ranges of 0.014-0.35, 0.064-0.358, 0.027- 0.875, 0.058-0.750, 0160-1.345 and 0.062-0.426 mg/kg, respectively. In addition, the organochlorine pesticides residues (p,p1-DDE, p,p1-DDT, and Chlorpyrifos) in the studied fish samples ranged between 0.02-2.13 mg/kg in the marine sites only. The thermal treatments via grilling were the most effective cooking method followed by baking to decrease the heavy metals concentrations in the fish species. Also, all detected pesticide residues and antibiotics in different fish species were decreased by cooking methods. Generally, the studied cooking methods significantly (p<0.05) decreased the total bacterial count and coliform counts in all treated samples by %. The frying method was the most effective cooking method in decreasing bacterial counts. In addition, neither Escherichia coli nor Vibrio spp was detected in the fish samples. Moreover, the studied cooking methods seemed to be suitable for decreasing the studied contaminants. Consequently, the farmed and wild fish species in the studied sites in Ismailia Governorate, Egypt, were safe and suitable for human consumption. Periodical monitoring of all sites for pollutants is highly recommended to ensure consumer protection.


Contaminants; Farmed fish; Traditional cooking methods; Heavy metals; Bacterial counts


Globally, aquaculture accounts for approximately half of the fish consumed and are considered among the quickest-growing food industries [1], with a growth rate of around 8.5% [2]. This trend is expected to continue, with aquaculture’s contribution to fish food supply expected to reach 60% by 2020 [3]. Moreover, aquaculture is the world’s quickest developing food production sector, with an annual ratio of growth of 37% registered in 2016 and an expected production of 109 million tons by 2030 [4].

Contaminants are usually present in natural environments as complex mixtures such as toxic heavy metals, Polycyclic Aromatic Hydrocarbons (PAHs), pesticides and bacterial contamination, providing many vital indicators for a complete diagnosis of environmental degradation. However, heavy metals are regarded as a severe threat to the aquatic environment because of their environmental stability and poisonous effects on aquatic organisms [5]. Heavy metal pollution can have destructive effects on the environment’s biological balance and various aquatic creatures [6]. Moreover, it might be accumulated in many tissues and organs of fish species [7], which can enter into the human metabolism through consumption, causing serious health risks. Because of the nutritional value of fish, it is necessary to define the level of heavy metals in aquatic organisms and its suitability for human utilization [8,9].

Antibiotics used in treating animal diseases and promoting animal growth are extensively used in fish feeds, and their presence is rising. For instance, sulfonamides and tetracycline are two classes of antibiotics generally utilized in aquaculture to treat infections in fish [10]. The excessive use of anti-microbials in aquaculture leads to antibiotic residue in consumed fish and fish products. This results in the undetected intake of antibiotics by the consumers with the probable changing of their normal flora which raises their vulnerability to infectious diseases by bacteria and to choose for antibiotic-resistant microbes [11]. Undetected antibiotic intake in food can be poisonous and cause allergy [12,13]. Therefore, there is a worldwide concern around the consumption of seafood having even low rates of antibiotics.

Similarly, PAHs are common organic contaminants in the environment that are recognized for their carcinogenic and mutagenic impacts and their ability to bioaccumulate in animal and human tissue [14]. PAHs are categorized as environmentally hazardous contaminants because of their known mutagenic, lipophilic and carcinogenic properties [15], in addition to their endocrine disrupting action [16]. In fish, PAHs have been known to be poisonous after biotransformation via poisonous metabolites that could be tied covalently to cellular macromolecules like RNA, DNA, and proteins, resulting in carcinogenesis, mutagenesis and cell damage [16]. PAHs reach the marine environment mainly by atmospheric depositions and surface runoff, where they may pollute aquaculture sediments and subsequently enter the food chain via fish to people [17]. In addition, Anderson, et al. [18] have reported that dietary exposure to PAHs is related to some human cancers.

Organochlorine Pesticides Residues (OCPs) are synthetic organic components with strong bonds among their chlorine and carbon compounds. Organochlorine pesticides are used for controlling pests, undesirable species of animals or plants causing harm or interfering with the production, storage, processing, and marketing of food, and agricultural products. It is important to remember that all pesticides must be regarded as active toxins [19]. OCPs are hydrophobic and steady components. Their photo-oxidation, low vapor pressure, and low chemical decomposition levels, have led to their accumulation in biological tissues and consequently enlargement in living organisms via food chains. Muir D, et al. [20] reported that biological samples like fish, terrestrial mammals, and sediments have greater OCPs than air or water making them more appropriate for routine monitoring of organochlorine residues and more important in the context of people’s exposure. The adverse effects of pesticide residues in fish include acute and persistent damage to the nervous system, damage to the reproductive organs, and dysfunction of the immune systems [21]. Many of persistent organochlorines and extremely poisonous organophosphates, that have been prohibited or extremely limited, are still marketed and used in many developing countries. Misuse of pesticides by individuals and weak national controlling plans are behind the negative impacts of these chemicals in developing countries [22].

Hormones are used for sex reversal and in artificial reproduction. The first is used when the growth rate is different among males and females. The second retains the production chain with the continuous production of eggs. This contrast among gender is commonly present in teleost fish and often happens during sexual maturity [23]. However, the usage of hormones in fish cultivating can have negative impacts, like possible environmental hazards and human health associated with hormone-dependent factors. Besides, its utilization exterior of good animal cultivation practices can impact the fish farming production system and the commercialization of this food product. The synthetic steroid 17 α-methyltestosterone is a particular male hormone commonly used to initiate sex reversal in fish [24]. The addition of steroids to the water containing sexually undifferentiated fish has also been successful in changing sex ratios and can provide aquaculturists with a safe and cost-effective to treat fry with food that contains 17α-methyltestosterone. The impact of these residues is great on human health since it may cause adulthood for girls and boys, carcinoma, increased embryo mortality, and liver tumors [25]. Sex steroid hormones can cause cancer in particular target organs (mammary gland, uterus, cervix, and prostate gland) and are characterized as carcinogens [26].

The pollution of fish with pathogenic bacteria from the aquatic environment may be a risk in all fisheries [27]. The level of fish pollution at the time of capture will depend on the microbiological quality of the water in which fish are caught. Many parameters will affect the bacteria such as water temperature, salt content, the proximity of harvesting regions to human habitations, amount, and source of fish food, and method of harvesting. The consumable flesh of the fish is ordinarily sterilized at the moment of capture, but bacteria are often growing on the gills, skin, and intestinal tract. In addition, fish take many microbes into their digestive tract from water, sediment, and food [28].

Generally, risk estimates for chemical residues depend on residue levels in raw food, even though a major amount of food is cooked or processed before consumption. To effectively evaluate the hazards of contaminants residues to humans, the impacts of cooking procedures (grilling, baking and frying) must be investigated [29]. Cooking methods are known to reduce the hazard of contaminants in fish. The decrease in the heavy metal concentrations is influenced by cooking procedures because of the discharge of these metals with the loss of drip, probably in relation to dissolvable amino acids and uncoagulated proteins bounded with metals. The cooking process may reduce the protein content of the fish parts [30]. Also, lipophilic OCPs are associated with the fat portion of foods. Hence, cooking methods that release or eliminate fat from fish will tend to decrease the total amount of OCPs in the cooked fish [31]. Furthermore [32] stated that heat treatment may diminish the antimicrobial activity of the antibiotic residues.

Therefore, the main objective of the study was to determine the level of some contaminants such as heavy metals, polycyclic aromatic hydrocarbons, organochlorine pesticides residues, hormones, antibiotics as well as total counts of aerobic and coliform bacteria. Moreover, the influence of traditional cooking methods (i.e., grilling, frying, and baking) on some contaminants in the flesh of wild and farmed fish species; commonly consumed in Ismailia Governorate, Egypt; to remove the consumer suspicious about the safety of fish consumption obtained from the studied sites.

Materials and Methods
Study areas and samples collection

Farmed Nile tilapia (Oreochromis niloticus) was collected from three fish farms in different sites of Ismailia Governorate: Farm 1 (F1), a private fish farm at Altal AlKabeir city, Farm 2 (F2) is a private fish farm at El Qantara Gharb region, Ismailia Governorate, and Farm 3 (F3), Institute of Aquaculture and Fish Technology of Suez Canal University. Moreover, wild Nile tilapia (Oreochromis niloticus) was also collected from freshwater (Ismailia Canal) (FW) and saltwater (Lake Timsah) (MW1). Also, the flathead gray mullet (Mugil cephalus) (MW2) and the thin lip gray mullet (Liza ramada) (MW3) were collected from Lake Timsah.

Fish samples having approximately similar size (average bodyweight 150-200g) were collected during the study period. The time and date of harvest were the same for both farmed and wild fish in each location but varied among locations. Immediately after collection, fish were kept in an icebox with a sufficient amount of flake ice and transferred to the laboratory. After collection, samples were transported to the Central Laboratory of Residue Analysis of Pesticides and Heavy Metals in Food (QCAP Lab) and kept frozen at −20°C until the time of carrying out the physicochemical and microbial assays.

Traditional cooking methods

Whole fish samples obtained from each farm, freshwater, and saltwater were divided into three groups then cooked by grilling, frying and baking methods using the methods described by El-Sherif SA, et al. [33]. For grilling, fish samples were pre-coated first with bran (a local routine) and grilled using an electrical grill machine at 180°C for 10 min. In the frying method, fish samples were pre-coated first with wheat flour (a local routine) and then fried at 160°C in deep sunflower oil in a frying pan for 8 min. Fish samples were placed on a metal tray and baked in an electric oven at 180°C for 20 min.

Analytical methods

Chemical analysis: Heavy metals involving Nickel (Ni), Cadmium (Cd), Cobalt (Co), Lead (Pb), Zinc (Zn), and Mercury (Hg) were determined via an Atomic Absorption spectrophotometer (Thermo Electron Corp, S series, AA spectrometer, Type S4 AA system, China) according to AOAC [34]. Total mercury was measured by an inductively coupled plasma mass spectrometry (ICP-MS) according to Bloxham MJ, et al. [35]. Antibiotics were determined by LC-MS according to the method described by Shin D, et al. [36]. PAHs were determined by GC according to Almatari MS, et al. [37]. Organochlorine Pesticides (OP’s) residues were determined using GCMS according to the modified QuEChERS sample preparation method described by Molina-Ruiz JM, et al. [38]. Hormones were measured by GC-MS according to Seo J, et al. [39].

Microbiological analysis: Ten grams from the blended sample were aseptically taken out of the Petri dish where 90 mL sterile buffered peptone water was subsequently added. Samples were then homogenized for 2 min. Aerobic Plate Count (APC) was determined using the pour plate method. Serial dilutions were prepared, and then, 1 mL of each was placed onto plate count agar media (Merck, Darmstadt, Germany). Then, the plates were incubated at 35°C for two days. The number of Vibrio species, 1.0 mL from each dilution was plated on Thiosulfate Citrate Bile Salts Sucrose (Oxoid) agar plates by the pour plate method. The inoculated plates were incubated for 18- 24 h at 37°C. For total coliform count, violet red bile agar was used as a medium (approximate formula per liter: 3g yeast extract, 7 g Peptone, 1.5 g bile salts, 10 g Lactose, 5 g sodium chloride, 0.03 g neutral red, 2.0 mg crystal violet and 15 g agar) plates were incubated at 35°C for 18-24 h. After incubation, the typical purple round bacterial colonies were enumerated. For Fecal coliform and E. coli, typical purple colonies were counted and were further confirmed by growing in Eosin Methylene Blue (EMB) agar plates. Presumptive colonies (blue-black colonies with a green metallic sheen and dark centers) on EMB agar were streaked on slant agar. Results are expressed as log CFU per gram of sample.

Statistical analysis: Analysis of variance was done using SPSS software (version 16.0 for Windows, SPSS Inc., Chicago). Bartlett’s multiple range tests were used to locate significance between treatment means at P ≤ 0.05.

Results and Discussion
Chemical analysis

Heavy metals analysis: The concentrations of heavy metals (Cd, Pb, Ni, Co, Zn and Hg) (mg kg-1) of weighted tissues of wild and farmed fish collected from the Ismailia Governorate are presented in figure 1. The highest Cadmium (Cd) concentration in the muscle of (0.083 mg/kg) was observed in marine Mullet (Liza ramada), while the lowest level (0.014 mg/kg) was detected in freshwater Nile tilapia. The data revealed a significant difference (P ≤0.05.) in Cd values between different fish samples at Ismailia Governorate. The values of Cd concentrations observed in fish samples agree with those values reported in the most reviewed literature, which reports Cd values in fish from the Pearl River Delta ranged from 0.03 to 1.57 mg/kg [40], from 0.01 to 0.04 mg/kg in fish from Fujian Province [41], and from 0.024 to 0.030 mg/kg in fish from China’s Yellow River [42]. To be specific [43] detected Cd mean value of 0.034 mg/kg in muscle tissues of tilapia, which is similar to the results reported in this study. According to the results recorded in the figure 1, Cd values were within the permissible limit (0.1 mg/kg in muscle) stipulated by WHO/FAO.

Figure 1: Heavy metals (mg/kg) concentrations detected in farmed and wild fish muscle.
F1: AlTal AlKabeir farm, F2: El Qantara Gharb farm, F3: institute of aquaculture and fish technology, FW1: freshwater fish, MW1: marine Nile tilapia (Oreochromis niloticus), MW2: marine Mullet (Mugil cephalus), and MW3: marine Mullet (Liza ramada). ND=Not detected, or the metals exist in amounts below the limit of detection.
LOQ: Limit of Quantification.
Means within the same column having different superscripts are significantly different at P>0.05 for treatments, while those within the same row with different superscripts are significantly different for farms.

The mean concentrations (mg/kg) of Lead (Pb) in muscles of various fish species in this study ranged from 0.064 to 0.358 mg/kg. Marine Nile tilapia (Oreochromis niloticus) of the Institute of Aquaculture and Fish Technology (F3) had the highest Pb concentration (0.358 mg/kg), whereas the marine Mullet (Liza ramada) showed the lowest concentration (0.064 mg/kg). By the way, Pb was not detected in El Qantara Gharb farm (F2) and freshwater Nile tilapia (FW1) samples in this study (Figure 1). In general, Pb concentrations measured in all fish samples collected from different locations were below the permissible limit (0.3 mg/kg in muscle) stipulated by WHO/FAO except for fish samples collected from F3.

The lowest concentration of Nickel (Ni) in fish species was 0.027 (mg/ kg) found in Nile tilapia from Altal AlKabeir farm, while the highest one of 0.875 (mg/kg) was observed in marine Mullet (Mugil cephalus). The sequence of concentration levels from the highest to the lowest for Ni was detected as follows: MW1>MW3>FW>F3>MW2>F1. Fortunately, Ni was not detected in fish samples from Qantara Gharb farm (F2). The data revealed a significant difference (P ≤ 0.05.) in Ni values between wild and farm fish samples at Ismailia. In addition, the concentration of Ni in fish samples collected in this study was within the range of Ni concentration (0.02 to 3.97 mg/kg) in a similar study reported by Türkmen M, et al. [44] in fish from the Marmara, Aegean, and Mediterranean seas. However, the results of Ni values, presented in figure 1, exceed the permissible limit (0.02 mg/kg in muscle) stipulated by WHO/FAO.

According to the results in figure 1, the range of concentration of Cobalt (Co) in fish muscles was 0.028-0.750 mg/kg in all studied fish species. The level of Co concentration was significantly higher (P ≤ 0.05.) in wild fish samples compared to farmed fish samples. The sequence of concentration levels from the highest to the lowest for Ni detected was as follows: MW3>MW2>MW1>FW>F1>F2>F3. In general, Co element concentration in all fish samples investigated in this study from different sources values did not exceed the permissible limit (1 mg/kg in muscle) stipulated by WHO/FAO.

The data in figure 1 showed that Zinc (Zn) was detected in all wild and farmed fish samples examined in this study. The level of Zn concentration in fish muscle ranged from 0.160 mg/kg for Nile tilapia from Altal AlKabeir farm to 1.345 mg/kg for marine Mullet (Mugil cephalus). The data revealed that there were significant differences (P ≤ 0.05.) in Zn values between wild and farmed fish samples at Ismailia Governorate, and all of them were higher than the permissible limit (0.04 mg kg-1) stipulated by WHO/FAO.

Finally, Mercury (Hg) was detected only in marine species ranging from 0.062 mg kg-1 to 0.426 mg kg-1. Fortunately, the levels of Hg concentration in all fish species were lower than the permissible limits of WHO/FAO. Comparable, results were reported by Morshdy A, et al. [45] were observed in Brush tooth Lizardfish and Mackerel fish samples collected from Egypt with Hg concentrations from 0.54 ± 0.03 to 0.56 ± 0.01 ppm, respectively.

Antibiotics and PAHs: In this study, out of 30 monitored antibiotics in fish samples, only two (Chlortotetracycline and Doxycycline) were detected in farmed fish. Doxycycline values ranged from undetected in F2 farm to 26 μg/kg in F1 and reached up to 35 μg/kg in F3. Tetracycline residues were only found in flesh fish of F3 farm (Table 1). Choi J, et al. [46] studied antibiotic residues in seven farmed fish species in Korea, and they detected only enrofloxacin (0.0305 mg/ kg) in Cyprinus carpio. Done HY, et al. [47] investigated 47 types of antibiotics in diverse cultivated fish (rainbow trout, Atlantic salmon, tilapia, and catfish) and shrimp retailed in the US. They identified five antibiotics (virginiamycin, sulfadimethoxine, epioxytetracycline, oxytetracycline, and ormetoprim) exceeding the detection limits. Barani A, et al. [48] found a high occurrence of tetracycline (63.1%), enrofloxacin (19.6%), florfenicol (40.6%), and sulfamethazine (17.4%) in rainbow trout samples from Iranian trout farms. On the other hand, PAHs as a common organic contaminant in the environment were not detected in any fish sample in this study.

Pesticide residues and Hormones: Data collected from this study revealed that only three organochlorine pesticides OCPs were detected in fish samples from marine and freshwater (p,p′-DDE, p,p′-DDT, and Chlorpyrifos). The data indicated that, p,p1 -DDE, and Chlorpyrifos range values were 0.02-2.01, undetected-2.044, and 2.05 to 2.13 mg/kg, respectively in Nile tilapia and marine Mullet in both salt and freshwater (Table 2). Also, the levels of OCPs in freshwater fish samples were lower than that in marine fish samples. The marine fish coming from the industrialized regions might have larger pollution rates. Previous research on wild tilapia has showed that DDE is the most prominent RDDT metabolite in fish tissue [49]. Yamashita N, et al. [50] reported that DDE was the most common pesticide residue in fish samples obtained from the Nile and Manzala lakes (7.6-67 ng/g).

  p, p1-DDE p, p1-DDE Chlorpyrifos
FW <LOQ ND 0.05b
MW1 0.02c <LOQ <LOQ
MW2 1.01b 1.067b <LOQ
MW3 2.01a 2.044a 2.13a

Table 2: Pesticide residues concentrations (mg/kg) in farmed and wild fish muscle.
F1: Altal AlKabeir farm, F2: El Qantara Gharb farm, F3: Institute of Aquaculture and Fish Technology, FW: freshwater fish, MW1: marine Nile tilapia (Oreochromis niloticus), MW2: marine Mullet (Mugil cephalus), and MW3: marine Mullet (Liza ramada).
ND=Not detected or the metals exist in amounts below the limit of detection.
LOQ: Limit of Quantification.
*Means within the same column having different superscripts are significantly different at ≤0.05.

Fortunately, hormones were not detected in any wild or farmed fish samples in this study. It should be noted that, fish and fish products that contribute to in human nutrition should be secure and free of potentially dangerous ingredients which affect human health [51].

Microbiological analysis

Fish is among the most perishable foods, primarily because of the activity of microorganisms on the surface of the freshly caught fish. Bacterial growth is commonly considered the primary reason for fish and fish product deterioration. As a result, it is suggested that bacterial count could be used as a quality indicator for fish products [52]. Aerobic Plate Counts (APC) are used as an acceptability index in fish products. As shown in table 3, it could be noticed that the low number of APC in the examined fish species demonstrated great safety and remained within the permitted limits which did not exceed 106 cell/g as stated by EOS [53] following Shen L, et al. [54], who documented that the total count of fresh fish <104 cells/g, sub fresh 104-106 and deteriorated fish >106 cells/g sample. The data revealed no significant differences (P ≤0.05.) in APC values between different fish samples. The values of bacterial counts were lower than those reported by Mohamed FSA, et al. [55], which showed that the total bacterial count in raw Nile tilapia was 2.11 × 105 cfu/g and 2.02 × 105 cfu/g sample.

  APC Coliform E. coli Vibrio
F1 5.17a 3.49a ND ND
F2 5.65a 5.31a ND ND
F3 5.20a 4.96a ND ND
FW 5.58a 5.48a ND ND
MW1 5.25a 4.34a ND ND
MW2 5.79a 4.50a ND ND
MW3 5.56a 4.52a ND ND

Table 3: Bacterial count (log cfu/g) in farmed and wild fish muscle.
F1 Altal AlKabeir farm, F2 El Qantara Gharb farm, F3 Institute of Aquaculture and Fish Technology, FW1 freshwater fish, MW1 marine Nile tilapia (Oreochromis niloticus), MW2 marine Mullet (Mugil cephalus), and MW3 marine Mullet (Liza ramada).
Means within the same column having different superscripts are significantly different at P ≤ 0.05.

The average count of coliform bacteria of the examined fish samples ranged from 3.49 to 5.48 log cfu/g. Because coliforms are not part of the natural bacterial flora in fish, their appearance shows the contamination rate of their ecosystem. In addition, the data showed no significant difference in coliform values between different fish samples.

Results in table 1 revealed that neither E. coli nor vibiro spp was detected in the investigated wild and farmed fish samples, indicating that the wild and farmed fish (Nile tilapia and Mullet) were obtained from Ismailia Governorate were microbiologically safe and had better quality for human consumption.

  Chlortetracycline Doxycycline
F1 <LOQ 26b
F3 36 35a

Table 1: Antibiotics concentrations (μg/kg) detected in farmed fish muscle.

The effect of traditional cooking methods on some contaminants

The effect of traditional cooking methods on heavy metals: The effect of traditional cooking methods on heavy metals (Cd, Pb, Ni, Co, Zn, and Hg) (mg kg-1) detected in farmed and wild fish muscle are shown in table 4. Cadmium concentration in farmed tilapia was 0.015 mg/kg and increased to 0.21 ppm by frying, while Cd was undetected when samples were either grilled or baked. These results of Cd concentrations in this study were in agreement with those found by El-Sherif SA, et al. [33], who observed that Cd levels in uncooked Nile tilapia (0.058 ppm) did not change when fish samples were cooked by frying (0.058 ppm), and reduced to 0.034 ppm after grilling.

Element Treatment F1 F2 F3 FW MW1 MW2 MW3 Mean
Cd Raw 0.015bc ND <LOQ 0.014bc 0.034b 0.029b 0.083a
Grilling ND ND ND ND ND ND <LOQ 0A
Frying 0.21a ND ND ND ND ND <LOQ 0.03A
Mean 0.07A 0A 0A 0A 0A 0A 0A 0A
Pb Raw 0.169ab ND 0.358a ND 0.086ab 0.097ab 0.064ab
Grilling <LOQ ND <LOQ ND ND 0.723b ND 0.10B
Frying <LOQ ND 0.432c ND <LOQ 1.234a ND 0.23A
Baking <LOQ ND <LOQ ND <LOQ 0.834b ND 0.11B
Mean 0C 0C 0.14B 0C 0C 0.93A 0C
Ni Raw 0.027c ND 0.478b 0.567b 0.875a 0.467b 0.654b
Grilling <LOQ ND 0.140b 0.436b 0.653b 0.345b 0.356b 0.27A
Frying <LOQ ND 0.189b 0.421b 0.678b 0.347b 0.365b 0.32A
Baking <LOQ ND 0.245b 0.510b 0.743a 0.365b 0.371b 0.31A
Mean 0A 0A 0.19A 0.45A 0.67A 0.76A 0.36A
Co Raw 0.074c 0.058c 0.028c 0.234b 0.650a 0.743a 0.750a
Grilling <LOQ <LOQ ND <LOQ 0.387c 0.293c 0.374c 0.15A
Frying <LOQ <LOQ ND <LOQ 0.431bc 0.298c 0.832a 0.22A
Baking <LOQ <LOQ ND <LOQ 0.452bc 0.264c 0.654ab 0.19A
Mean 0C 0C 0C 0C 0.42B 0.28B 0.62A
Zn Raw 0.160c 0.563bc 0.214c 0.865ab 0.672bc 0.942ab 1.345a
Grilling 0.033c 0.378bc 0.021c 0.476bc 0.382bc 0.487bc 0.832bc 0.37A
Frying 0.101bc 0.389bc 0.301bc 0.432bc 0.465bc 0.567bc 1.905a 0.59A
Baking 0.185bc 0.412bc 0.156bc 0.561bc 0.498bc 0.593bc 1.04ab 0.49A
Mean 0.10B 0.39B 0.15B 0.48B 0.44B 0.54B 0.25A
Hg Raw ND ND <LOQ ND 0.062 0.353a 0.426a
Grilling ND ND ND ND ND <LOQ ND 0C
Mean 0C 0C 0C 0C 0C 0C 0C

Table 4: Effect of traditional cooking methods on heavy metals concentrations (mg/kg) detected in farmed and wild fish muscle.
F1: AlTal AlKabeir farm, F2: El Qantara Gharb farm, F3: Institute of Aquaculture and Fish Technology, FW1: freshwater fish, MW1: marine Nile tilapia (Oreochromis niloticus), MW2: marine Mullet (Mugil cephalus), and MW3: marine Mullet (Liza ramada).
ND=Not detected, or the metals exist in amounts below the limit of detection.
LOQ: Limit of Quantification.
Means within the same column having different superscripts are significantly different at P ≤ 0.05 for treatments, while those within the same row with different superscripts are significantly different for farms.

The lead concentrations were reduced from 0.097 of marine Mullet (Mugil cephalus) flesh to 0.834 (mg/kg) by baking and 0.723 by grilling. However, frying increased Pb concentration to 1.234 and 0.432 (mg/kg) for Mullet (Mugil cephalus) and Nile tilapia. These findings agreed with those results reported by El-Sherif SA, et al. [33] in grilling Nile tilapia and mullet fish fillets from Wadi El-Rayan Lake, but differentiated in frying, where Pb concentrations were 0.415 and 0.196 ppm for uncooked Nile tilapia and mullet fish fillets, and reduced to 0.373 and 0.145 in grilled and 0.388 and 0.185 in fried samples, respectively. Also, the results were in agreement with those stated by Perello G, et al. [56], who revealed that the concentrations of Pb in tuna and sardine were higher in fried samples and lower in grilled samples. Therefore, the decrease in trace minerals levels as influenced by cooking procedures might be attributed to the release of these coagulated proteins bounded with metals, whereas the rise in minerals is associated with a reduction in the moisture content during cooking [57].

Also, Ni and Co concentration of examined fish samples decreased significantly by grilling followed by baking. Conversely, frying increased Ni and Co values in some fish samples.

It was noticed that Zn concentrations of marine Nile tilapia were 0.672 mg/kg, decreased to 0.465, 0.498, and 0.382 (mg/kg) for fried, baked, and grilled samples, respectively. El-Sherif SA, et al. [33] reported that Zn levels were 0.221 and 0.086 ppm in Nile tilapia and mullet fish fillet from Wadi El- Rayan Lake rose to 0.263 and 0.116 ppm by frying method and reduced to 0.089 and 0.038 ppm by grilling method.

Total Mercury (Hg) concentrations found in the muscle of the studied fish samples revealed that Hg concentrations were below the maximum allowed for fish both in raw and cooked fish (0.5 mg kg). This implies that raw and cooked fish meet the existing safety criteria for wild and farmed fish at Ismailia Governorate. Furthermore, these findings suggested that, depending on the fish species, certain culinary procedures could help reduce total mercury levels in fish.

Therefore, it could be concluded that the concentrations of all determined heavy metals in the examined samples were lower than the permissible limit set by FAO/WHO [58]. Furthermore, grilling was the most effective method for decreasing all heavy metals, followed by baking. In contrast, frying method increased the majority of them. Therefore, cooking by grilling followed by baking methods was found to be more suitable for human consumption than the frying method for decreasing the harmful effects of heavy metals.

As there were only two antibiotics (Chlortetracycline and Doxycycline) detected in farmed fish, the antibiotics concentrations of baked, grilled, and fried fish samples were not detectable (below limits of detection) Uno K, et al., [59] reported that OTC residues were lower in all cooked samples than in the corresponding raw samples. Also [60] stated that application of heat treatment like roasting and frying may lead to destroying of all drug residues.

The effect of traditional cooking methods on pesticide residues: Because only three organochlorine pesticides were detected in the fresh fish samples from marine and freshwater (p,p′-DDE, p,p′-DDT, and Chlorpyrifos). Therefore, the concentrations of OCPs residues were investigated in cooked (grilled, fried, and baked) samples. OCPs residues concentration were not detected (data were not shown) after heat treatments of samples (Reduction rate 100% in most treatments). This result is supported by the results of Amal ME, et al. [61], who documented that OCPs levels (α-HCH, γ-HCH, and Endrin) in Tilapia nilotica and Clarias lazera fish taken from fish markets in Gharbia, Egypt were reduced after frying, grilling, and boiling. In Tilapia nilotica samples, OCPs concentrations were reduced by about 85, 79, and 80% by frying method, and 87, 52, and 100% by grilling, respectively. In Clarias lazera samples, the OCPs concentrations were reduced by 100, 54, and 83% by frying and 100, 50, and 100, respectively, by boiling.

Comparable results were detailed by Hassanen FS, et al. [62], who studied the effect of the grilling cooking method on OCPs concentrations in raw Nile tilapia (Oreochromus nilotica) collected from three different areas. The results showed a significant decrease in OCPs concentrations by a ratio of 11% to 100% by grilling depending upon the type of pesticide residue and variation in localities.

Domingo JL [63] explained that the reduction of OCPs residues by frying was because of increased loss of fats and oils with high heat treatment, which caused OCPs to be drained out with the lost fats and oils and in oil dripping by grilling. Furthermore, the decrease rate in OCPs residues in cooked fish varied relying on pesticide solubility, fish species, and cooking procedure [31].

The effect of traditional cooking methods on bacterial counts: The effect of traditional cooking methods on bacterial count (log cfu/g) in fish samples is shown in table 5. APC and coliform counts were reduced in all cooked fish samples. APC of raw Mugil cephalus was 5.79 and decreased to 3.93, 3.11, and 4.12 (log10 cfu/g) when grilling, frying, and baking were used, respectively. The APC of marine Nile tilapia (Oreochromis niloticus) flesh was 5.25 and decreased to 4.47, 4.21, and 4.67 when grilling, frying, and baking were used, respectively. This reduction in bacterial counts might be attributed to heat treatment applied during cooking methods. So, the greatest reduction was noted in fried samples compared with raw fish samples, followed by grilled and baked fish samples. These findings agreed with those published by El-Sherif SA, et al. [33] who found that APC of raw tilapia and mullet fish were 2.35 and 2.01 respectively, reduced to 1.95, 2.10, and 2.15 for tilapia fish and to 1.70, 1.72, and 1.95 (log10 cfu/g) for mullet by frying, grilling, and boiling, respectively.

Bacterial Count Treatment F1 F2 F3 FW MW1 MW2 MW3 Mean
APC Raw 5.17a 5.65a 5.20a 5.58a 5.25a 5.79a 5.56a  
  grilling 4.34a 4.80a 4.51a 4.76a 4.47a 3.93a 5.10a 4.55A
  Frying 3.86a 4.78a 4.26a 4.47a 4.21a 3.11a 4.48a 4.16A
  Baking 4.51a 5.35a 4.67a 5.34a 4.67a 4.12a 5.34a 4.85A
Mean   4.23a 4.97a 4.48a 4.84a 4.45a 3.72a 4.97a  
Coliform Raw 3.49a 5.31a 4.96a 5.48a 4.34a 4.50a 4.52a  
  Grilling 3.24ab 4.84a 4.51ab 4.78a 3.38ab 4.45ab 4.52ab 4.25A
  Frying 2.74b 4.64ab 4.21ab 4.58ab 3.16ab 3.72ab 4.52ab 3.93A
  Baking 3.27ab 5.10a 4.72a 4.89a 3.54ab 4.39ab 4.52ab 4.34A
Mean   3.10C 4.86A 4.48AB 4.75A 3.36BC 4.18ABC 4.52A  

Table 5: Effect of traditional cooking methods on bacterial count (log cfu/g) in farmed and wild fish muscle.
F1: AlTal AlKabeir farm, F2: El Qantara Gharb farm, F3: Institute of Aquaculture and Fish Technology, FW1: freshwater fish, MW1: marine Nile tilapia (Oreochromis niloticus), MW2: marine Mullet (Mugil cephalus), and MW3 marine Mullet (Liza ramada).
ND=Not detected, or the metals exist in amounts below the limit of detection.
LOQ: Limit of Quantification.
Means within the same column having different superscripts are significantly different at P ≤0.05 for treatments, while those within the same row with different superscripts are significantly different for farms.


In This study, the obtained results showed that most determined heavy metals, antibiotics, PAHs, OCPs, concentrations, and microbiological counts in flesh of wild and farmed fish species obtained from Ismailia Governorate were lower than the permissible limits. Hormones were not detected. Cooking methods further reduced contaminants; grilling being the most method for reducing heavy metals, antibiotics, and OCPs, followed by frying and baking. Furthermore, frying was the most effective method for reducing APC, followed by grilling and baking. Therefore, the traditional cooking methods (grilling, frying and baking) were suitable for decreasing the studied hazardous pollutants. Hence, the wild and farmed fish species obtained from the studied sites in Ismailia, Egypt were safe for human consumption removing the consumer suspicious about pollution of farmed fish as compared to wild fish in the studied area. Periodical monitoring of all sites for pollutants is highly recommended to ensure consumer protection.

Data Availability

All the authors have confirmed that the data supporting the results obtained from this study are present in this article.


Conflict of interest: The authors declare no competing interests.


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Citation: Aref S, Morsy N, Habiba RA, Abdel-Daim M, Zayet F (2022) Influence of Traditional Cooking Methods on the Concentrations of some Contaminants in wild and farmed fish in Ismailia Governorate, Egypt. Nutr Food Technol Open Access 8(2): 6086.181

Copyright: © 2022 Aref S, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Publication history: 

  • Received date: 22 Jun, 2022

  • Accepted date: 18 Jul, 2022

  • Published date: 25 Jul, 2022