Omega-3 Fatty Acid Composition of Persian Gulf Fishes

Abstract

The aim of this study was to investigate the content of omega-3 fatty acids in Persian Gulf fishes. The fishes were collected from Persian Gulf and the content of fatty acids in the head, muscle, and liver of fishes were determined. Quantitative analysis of fatty acids was performed by gas chromatography (GC) and methylmyristate was used as the reference material. GC and mass spectrometer (GC- mass) was applied for qualitative analysis and cod liver oil with all of omega-3 fatty acids was used as standard. Ghezel ala, Zamin kan-e-dom navari and Sorkhu mahi had maximum levels of omega-3 in total body. Halva Sefid, Gish-e-deraz baleh and Shamshiri were poor sources of omega-3. The liver of fish had the most content of omega-3 fatty acids followed by muscle and head, respectively.

Keywords:

• Omega-3
• Fatty acids
• Fish
• Liver

INTRODUCTION

Human beings need omega-3 and omega-6 as essential fatty acids because the body does not produce them and they should be taken from diet. Omega-3s are called “good fats” and are found mostly in seafood and flaxseed products (particularly linolenic acid). Omega-3 fatty acids are long-chain polyunsaturated fatty acids (18–22 carbon atoms in chain length) that include Alpha-linolenic Acid (ALA), Eicosapentaenoic Acid (EPA), and Docosa Hexaenoci Acid (DHA).[1] EPA and DHA are the two principal fatty acids found in fish. ALA is highly concentrated in certain plant oils such as flaxseed oil and to a lesser extent in canola, soy, perilla, and walnut oils. Omega-3 free fatty acids are:

•	an important source of energy;
•	a component of cell membranes;
•	a modulator of gene expression;
•	a precursor of eicosanoids;
•	a preventive agent for cardiovascular disease, autoimmune disease, and cancers;
•	a modulator of inflammation and thrombosis; and
•	an important factor for brain development and visual acuity.

It has been reported that taking of 0.5–1.8 grams of EPA and DHA daily (either as fatty fish or supplement) reduces the risk of coronary heart disease and its related mortality.[2] The American Heart community suggests using fish at least twice a week. Different studies have shown that fish is the most important source of omega-3 fatty acid. The results of the freshwater/saltwater fish comparisons clearly established that some freshwater fishes are good sources of EPA and DHA as two types of omega-3 fatty acids.[3] Consumption of at least two servings of fish per week has been recommended by the American Heart Association (AHA) to achieve cardioprotective effects. Fishes are the biggest and the most varied group of aquatic vertebrates. Iran has various species of fishes depending on bring and freshwater. Freshwater fishes in Iran include 13 types and 25 families.[4,5] The aim of this study was to investigate omega-3 fatty acid contents in different species of fishes and also in different parts of fish.

MATERIALS AND METHODS

Fishing for thirty species in cool season was performed in a hunting area of Boushehr and Hormozgan (from Persian Gulf). After catching, the fishes were transferred to a freezer within one hour. After freezing, they were transferred to Shiraz Fisheries Research Laboratory, Natural Resource and Agricultural Research Center. After identifying them, their height and weight were measured, and then a three-kilogram sample of each fish was separated and labeled; then the fishes were transferred to a basic sciences laboratory of Shiraz Veterinarian College. Methylated fatty acids of these fishes were prepared using cod liver oil because there were no any standard. In this sample, fatty acids were separated, methylated and then were injected to gas chromatography (GC) system.

The fish that was maintained at ice block in the refrigerator was dissected at lab temperature, and the tail and head was removed. The liver and muscle were purely excised. Head was placed at meat rotator for fully softening, and liver was fully softened by chins mortar. Then three samples of fully softened muscle, head, and liver were prepared for the next stage. After weighting the samples, each sample was poured into separate beakers, and 40 cc of chloroform-met and mixed-solution was added at the ratio of 2 to 1. The mixed solution was passed through filter paper. It was poured at separated funnel and mixed for a second minute and maintained stationary for a five minute for separating two phases. The lower phase was added to the previous separated and upper phase was thrown away. A little of this solution was sent for measurement of fat and fatty acids. Before pouring of fat-solution at measuring dish, the dish was weighted. Then, 15cc of chloroform-ethanol solution was added to the fat, and the sample was maintained in a wrapped tube in the refrigerator.

Three samples were poured into separate Erlenmeyer flasks, and 50 cc of Potas-Alcohol solution 10% was added, a magnet was thrown on it, and it was placed on the mixer for four hours. Then 50 cc of distilled water was added and mixed finely for two minutes. At this condition, non-soupy substance was dissolved. Lower phase was added to the previous solution and upper phase was washed at ethanol-alcohol and water. 30 cc of HCl was added to the product solution. At this condition free fatty acids were separated. 50 cc of Petroleum benzene and diethyl ether at the same proportion was divided and mixed for two minutes completely and fatty acids were placed at the upper phase that poured at balloon.

Two milliliters of sulfuric acid (4%) and alcohol was added to the fatty acids product. Then it was placed at benmari (75–80) for 30 min. 20 cc of petroleum benzene was added and mixed finely. After mixing, the later phase (water) was thrown and the upper phase was separated. One gram of Na- carbonate was added and mixed and passed from filter-paper and then 1 gram of Na-sulfate was added and mixed and passed from filter-paper. The separated solution was poured at the small tube and was vaporized at 45°C, and then 1 cc of N-Hexin was added to it and covered tightly. At this condition, sample was prepared for injection to GC apparatus. All stages were done at 90 samples (30 fish species).

RESULTS

The scientific and local name of fish has been shown in Table 1. In GC results, there were 8 peaks; 5 peaks include unsaturated fatty acids, and 3 peaks include linolenic acid omega-3 fatty acids (EPA and DHA). The results of omega-3 and non omega-3 fatty acids are shown in 1–3. In these figures, data are separated according to different part including head, muscle, and liver. In these figures, undefined fatty acids are those fatty acids that were not mixed with standard sample thus they have not been identified by GC mass system. Head in Shourt (34%), Ghezel ala Rangin Kamani (31.70%) and Kijar mahi (31%), had the most proportion of omega-3. In liver tissue of Zamin Kan-e-Dom Navari (65%), Koter-e-Sadeh (49%), Ghezel ala (34.40%), there was the highest rate of omega-3. Ghezel ala, Zamin Kan-e- Dom Navari and Sorkhu mahi had the maximum content of omega-3 in total body. The liver of fish had the highest content of omega-3 fatty acids and the muscle and head were the next, respectively. However, the highest proportion of omega-3 fatty acid was found in the liver of Zamin Kan-e- Dom Navari with 65%.

Table 1 Scientific name and local name of 30 fish species

Scientific name	Local name
Oncarhynchus mykiss	Ghezel ala rangin kamani
Rutitus frisiikutum	Mahi sefid
Otolithes rubber	Shourideh
Sillayo sihama	Shourt
Pampu argenters	Halva sefid
Lutjanus malabricvs	Sorkhu mal bari
Solea elongate	Kafshak-e-riz
Pomadasys Kaakan	Sangsar-e-mamuli
Sphyreena jello	Koter-e-sadeh
Rachycentron candaum	Sokalla
Mugil cephalus	Kefal-e-rah rah
Lethrinus nebulosus	Sorkhou
Scomberomorus yuttatus	Ghobad
Eleutheronema tetraductylum	Rasgo-e-mamuli
Saurida tumbip	Kijar-e- bozorg
IIisha meyaloptera	Shamshak-e-bozorg
Carangoiedes armatus	Ghishe-e- deraz baleh
Platycephalus indicus	Zamin kan-e-dom navari
Tylosurus crocodiles	Menghar mahi shekarchi
Cynoglossus bilineatus	Zaban gavi char khat
Terapon theraps	Yalli-poulak dorosht
Plectrohinchus flavoma culatus	Khennu limui
Epinephelus coicoides	Hamur-e-mamuli
Scomberoides commersonnianus	Sarom-e- dahan bozorg
Capoeta damacina	Saiiar mahi
Capoeta buhsei	Shamshiri
Oncarhynchus mykiss	Ghezel ala
Muroenesox cinereus	Mar mahi-e- tiz dandan
Capoeta Barroisi	Dasht-e-arjani
Ciprinus Carpio	Kapour-e-mamuli

Figure 1 Comparison of omega-3 fatty acids in head portion of 30 species fishes.

Figure 2 Comparison of omega-3 fatty acids in muscle portion of 30 species fishes.

Figure 3 Comparison of omega-3 fatty acids in liver portion of 30 species fishes.

DISCUSSION

In this research, the percentage of different types of omega-3 and non omega-3 fatty acids was determined in different parts of the body (head, muscle and liver) of 30 species of different fishes of Persian Gulf. According to the results, the head in Shourt (34%), Ghezel ala Rangin Kamani (31.70%), and Kijar mahi (31%), had the most proportion of omega-3. A previous study showed that content of omega-3 in head and muscle of Antarctic fish is the same, and it was concluded that head is as useful as muscle.[6] In 2001, Bagh Malaee et al. showed that Shouride of Persian Gulf and Whitefish of Caspian Sea have maximum level of omega-3 fatty acid in muscles and over all fatty acid content of Persian Golf and Caspian Sea fish are the same. That study assessed the content of fatty acids only in muscle portion of fish.[7] In the present study, Ghezel ala, Zamin Kan-e- Dom Navari and Sorkhu mahi had the maximum content of omega-3 in total body. Many studies showed that many popular fish were poor sources of omega-3 fatty acids.[3,8] In this study, fish species, including Halva Sefid, Gish-e-Draz Baleh and Shamshiri were poor sources of omega-3 fatty acids. In the liver portion of Zamin Kan-e-Dom Navari (65%), Koter-e-Sadeh (49%), Ghezel ala (34.40%), there was the highest rate of omega-3. In 2001, Azin et al. showed that amount of omega-3 fatty acid in liver and tissue of Persian Gulf sharks are between 29.81–18.02% and 20.51–2.21% and the type and rate of lipids and fatty acids depend on spice, gender, age, the fishing location, weight and diet of sharks.[9] In addition, other studies like ours showed that fish liver has the highest rate of fatty acid in comparison with other organs.[6] It has been shown that there is a direct relation between the environment temperature and the content of unsaturated fatty acids (EPA).10–12 Analysis of fatty acid profiles of kingfish in Oman Sea, which is a region near to Persian Golf (region of present study) with similar climate and environment, showed that the omega-3 content of all samples was 5–8 folds higher than omega-6 fatty acid. Omega3/omega6 FA ratios was higher in Kingfish from the Batinah region than samples from the Dhofar region.[13]

The biological condition of Persian Gulf is different from other waters in different parts of the world, and this causes differences in the rate of omega-3 fatty acids in special species of Persian Gulf fish. This study showed that the liver portion of fish had maximum level of omega-3 and in muscle it was more than head. Thus, for obtaining maximum amount of omega-3, it is recommended to eat all the fish tissues other than muscle alone; similar results have been obtained in other assessment too.[9,14,15]

ACKNOWLEDGMENT

The authors would like to thank Farzan Institute for Research and Technology for technical assistance for this research work.