FNS  Vol.11 No.6 , June 2020
Fatty Acid Profiles of Livers from Two Marine Fishes Inhabiting Sudanese Red Sea Coast
Abstract: Fish livers a good source of long-chain polyunsaturated fatty acids and omega 3, are usually discarded as a waste when fish are processed for human consumption in Sudan. Highly fresh Triaenodon obesus and Hipposcarus harid fish were purchased from Port Sudan fish central market during December 2014. The fatty acid profiles of the livers of these commercially important fish were determined. The polyunsaturated and saturated fatty acids ratio in the livers oil of T. obesus and H. harid was 1:2.2 and 1:1.38, respectively. The Palmatic (16:0), Pentadecenoic (12:0) and Arachidic acids were the highest in both species. The poly chain unsaturated fatty acids Linolenic (18:3n - 3), Eicosapentaenoic (20:5n - 3) and Docosahexaenoic (22:6n - 3) were detected in the liver of both species. The highest values of above poly chain unsaturated fatty acids were detected in T. obesus.

1. Introduction

The Red Sea State is a semi-desert with poor agricultural and animal resources. Fish can be used to complement amino and fatty acids needs and promote the quality of the diet [1]. Hamza et al. [2] [3] examined fish consumption in Port Sudan and found that 93.8% of the population used to have fish in their diets. They found that the average fish consumption/capita at the Red Sea State reached 9.6 kg/year. This is about half the world/capita consumption of 18.9 kg per year [4].

The total oil and fatty acid composition of fish varies according to several factors, such as fishing season, geographical location, size, sex, and reproductive cycle period [5]. The omega-3 is mainly present in marine algae and fish. Fish liver oil is in general rich in omega-3 fatty acids, including Alpha-linolenic acid (18:3), Eicosapentaenoic acid (20:5) and Docosahexaenoic acid (22:6), [6]. Humans can’t synthesize fatty acids but rely on the food chain or tablets. Algae and fish are the best sources of long chain polyunsaturated fatty acids (n − 3 LCPUFAS) [7]. Marine fishes contain a significant amount of LC-PUFAs, particularly DHA (docosahexaenoic acid, C22:6ώ3) and EPA (Eicosapentaenoic acid, C20:5ώ3) [8]. Marine fishes possess a high proportion of total omega 3/omega 6 fatty acids [9]. According to Guil-Guerrero et al. [10] (2011) liver oil of marine fish species constitutes a rich source of n − 3 LCPUFA, especially of EPA and DHA.

Polyunsaturated fatty acids (mainly the n3 and n6 PUFAs) combat cardiovascular diseases, high blood pressure, cancers, Alzheimer’s disease and neurodevelopment status in infants [11] [12]; promote immunity [13] and heath due to its richness in vitamins A and D [14].

According to Randall [15], sharks and parrotfishes are among the most important commercial fish stocks in Sudanese Red Sea waters. It is known that the locals extract the oil from livers of T. obesus and H. harid by exposing them to sun. The extract is used as a traditional medication for cough and sneezing especially in infants.

The objective of this work is to study the fatty acids profile of T. obesus and H. harid to lay a base line data for a pharmaceutical industry.

2. Materials and Methods

2.1. Samples Collection

Ten highly fresh specimens of T. obesus and of H. harid were purchased from Port Sudan fish central market during December 2014 and chilled in an ice box and immediately taken to the laboratory. The total length, standard length and body weight of each specimen was recorded.

The abdomen of each fish was open, and the liver was carefully removed and weighed to 0.1 g separately using an electrical balance. Each liver was kept frozen at −30˚C until analysis.

2.2. Fatty Acid Analysis

2.2.1. Extraction of Oil

Fish whole livers were thawed at room temperature. For each liver the water extracted with the oil was removed by centrifuging following Nuria et al. [16]. The percentage of oil yield was calculated as:

Oil ( % ) = Weight of extracted oil × 1 00 Weight of liver

Fatty acids of each liver specimen were determined based on the method of Farhat and Shakoor [17]. Methylation of fatty acids in oils was carried out according to Cocks and Rede [18].

2.2.2. Gas Chromatography (GC)

The FAME samples of each fish species were examined by Gas Chromatography (GC-2010) using Helium as a carrier gas and SGforte BPX 30 column (30 m × 0.25 mm ID × 0.25 µm film thicknesses). The initial temperature of the column was set and held at 50˚C for 1 min. The temperature then raised at 2˚C/min to 188˚C which was held for 10 min followed by an increase at the same rate to 250˚C where it was held for 4 min and then returned to the initial temperature. The extraneous combined FAME standard used to discover and identify the peaks. Fatty acids were measured by equating their peaks with the relevant peak areas of the corresponding standard fatty acids where each fatty acid then stated as a percentage of the total fatty acids measured [17].

2.3. Statistical Analysis

SPSS programme was used to analyze the data. The results presented as the mean ± standard error of the mean.

3. Results and Discussion

The present study, the first of its kind in Sudan, tapped the fatty acid profiles of the fish liver of T. obesus and H. harid. Fish livers, which are usually discarded when fish are processed in Port Sudan fish market, were found to be a potential source of LCPUFAs. The livers constitute a substantial portion of fish waste. According to Hamza et al. [3] the total fish waste is about 634 kg/day.

3.1. Morphometric Measurement

The averages of total length, standard length, body weight, the liver weight of T. obesus were 78.18 ± 3.15 cm, 55.8 ± 2.31 cm, 2669.6 ± 831.31 g and 78.18 ± 3.15 g, respectively. In H. harid the corresponding values were 29.25 ± 0.57 cm, 24.10 ± 0.35 cm, 385 ± 43.22 g and 15.88 ± 2.10 g, respectively (Table 1). The variation in morphometric parameters of two fish species is due to family and species differences.

3.2. Fatty Acids Profiles

The oil extracted from T. obesus and H. harid liver is yellow to brown with a

Table 1. Some parameters of Triaenodon obesus and Hipposcarus harid.

strong flavour and is insoluble in water. The weight of shark varies from 5% [19] to 20% [20] the shark’s body weight. This calls for tapping liver oil from sharks in the Sudanese coast

The study showed that the percentage of the fat exceeds 50% of the liver weight thus offering a potential commercial source of fats (Table 1). According to Guil-Guerrero et al., [10] fish fats content depends on season of capture, geographical location, water temperature, size and sex of the fish and its reproductive cycle at the time of capture.

The number of saturated fatty acids (SFAs) recorded in livers of T. obesus and H. harid were 12 and 6 with mean concentration 8.89% ± 1.89% and 13.78% ± 3.93%, respectively. Unsaturated fatty acid number were 10 and 8 with a mean concentration 19.54% ± 3.67% and 18.96% ± 4.05%, respectively (Table 2 and Table 3). The percentages of unsaturated fatty acids (USFAs) were higher than saturated fatty acids (SFAs) in T. obesus and H. harid livers. This is in agreement with Gunstone and Norris [21].

The value of SFAs content in oil of H. harid was higher than in T. obesus. Vice versa holds true in case of USFAs. This may reflect differences in diet and bioaccumulation of fatty acids in the food chain. This is in line with Nelson et al. [22] and Nichols et al. [23].

The liver fatty acids profile in T. obesus and H. harid showed that C15:0, C16:0 and C20:0 were the main SFAs; C15:1, C16:1 and C17:1 were the main monounsaturated fatty acids; while C22:6n − 3 (DHA), C20:5n − 3 (EPA) and C18:3n − 3 (ALA) were the main PUFAs (Table 2 and Table 3).

Table 2. Saturated fatty acid profiles of liver from Triaenodon obesus and Hipposcarus harid, BDL = Beyond Detection Limit.

Table 3. Unsaturated fatty acid profiles of liver from Triaenodon obesus and Hipposcarus harid BDL = Beyond Detection Limit.

Saturated Palmitic and Pentadecenoic acid showed high percentages in oil fraction of T. obesus and H. harid which is useful for formulations based on fish oil. Fishes from warm waters tended to show high levels of Palmitic and Stearic acids compared with those from cold waters. This is probably due to environmental metabolic differences [24]. In T. obesus and H. harid ALA recorded high value followed by EPA confirming Gunstone and Norris [21] who stated that ALA and EPA are the dominant fatty acids in oil of marine fishes. High values of LCPUFAs especially EPA and DHA except ALA were detected in T. obesus when compared with H. harid (Table 3). Sargent et al. [25] and Saito et al. [26] attributed such variations to the species habitat, diet and ecological conditions.

The PUFAs:SFAs ratio in livers oil of T. obesus and H. harid were 1:2.2 and 1:1.38, respectively. Triaenodon obesus showed the highest level of USFAs, EPA and DHAs, and the lowest level of SFAs. Such levels seem beneficial to human health [27]. According to Wetherbee and Nichols [28] the composition of the liver lipids of sharks varies according to species, season and other biological factors.

4. Conclusion

The liver of T. obesus and H. harid contain high concentrations of lipids exceeding 50% of its wet weight. The value of UFAs in the liver oil in T. obesus and H. harid were higher when compared with SFAs. Triaenodon obesus showed the highest level of UFAs, EPA and DHA and the lowest level of SFAs. The liver of the two species is a rich source of n − 3 LCPUFA, especially EPA and DHA and ALA. The findings call for joint research between fish biologists, chemists and pharmacists to tab the medication opportunities of marine fish livers from Sudanese Red Sea.

Cite this paper: Hassan, H. , Mohammed, S. , Elamin, S. and Alraih, E. (2020) Fatty Acid Profiles of Livers from Two Marine Fishes Inhabiting Sudanese Red Sea Coast. Food and Nutrition Sciences, 11, 571-577. doi: 10.4236/fns.2020.116040.

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