Food Bioactive Compounds against Diseases of the 21st Century 2016View this Special Issue
Research Article | Open Access
DHA and EPA Content and Fatty Acid Profile of 39 Food Fishes from India
Docosahexaenoic acid (DHA) is the principal constituent of a variety of cells especially the brain neurons and retinal cells and plays important role in fetal brain development, development of motor skills, and visual acuity in infants, lipid metabolism, and cognitive support and along with eicosapentaenoic acid (EPA) it plays important role in preventing atherosclerosis, dementia, rheumatoid arthritis, Alzheimer’s disease, and so forth. Being an essential nutrient, it is to be obtained through diet and therefore searching for affordable sources of these ω-3 polyunsaturated fatty acids (PUFA) is important for consumer guidance and dietary counseling. Fish is an important source of PUFA and has unique advantage that there are many food fish species available and consumers have a wide choice owing to availability and affordability. The Indian subcontinent harbors a rich fish biodiversity which markedly varies in their nutrient composition. Here we report the DHA and EPA content and fatty acid profile of 39 important food fishes (including finfishes, shellfishes, and edible molluscs from both marine water and freshwater) from India. The study showed that fishes Tenualosa ilisha, Sardinella longiceps, Nemipterus japonicus, and Anabas testudineus are rich sources of DHA and EPA. Promotion of these species as DHA rich species would enhance their utility in public health nutrition.
Fatty acids play crucial role in maintaining health and cellular functions. The preventive effect of ω-3 fatty acids on coronary heart disease is based upon hundreds of experiments in animals, humans, tissue culture studies, and even clinical trials  which first became apparent in the investigation on the health status of Greenland Eskimos who consumed a very high fat diet from seal, whale, and fish and yet had a low incidence of coronary heart disease . Further studies have shown that the kind of fat the Eskimos consumed contained large quantities of ω-3 fatty acids: EPA (20:5) and DHA (22:6). Moreover, deficiencies of these fatty acids lead to a host of symptoms and disorders. Among the long chain omega- (ω-) 3 fatty acids (LC-PUFA), docosahexaenoic acid (DHA) is the principal PUFA constituent of brain neurons, retinal cells, and primary structural component of skin, sperm, and testicles. Apart from being an important structural component of cellular membranes, it performs varieties of functions in a number of cellular processes like transport of neurotransmitters and amino acids and modulates the functioning of ion channels and responses of retinal pigments . DHA has been shown to be particularly important for fetal brain development, optimal development of motor skills and visual acuity in infants, lipid metabolism in children and adults, and cognitive support in the elderly . DHA along with eicosapentaenoic acid (EPA) play important role in preventing atherosclerosis, dementia, rheumatoid arthritis, diseases of old age like Alzheimer’s disease (AD), and age related macular degeneration (AMD) [4–6]. Cardiovascular disease (CVD) is the leading cause of mortality in many economically developed countries and DHA plays an important role in preventing CVDs.
DHA is an essential nutrient as it is synthesized in very less quantity in human body and is obtained mainly through diet. Cold water marine fishes are the important dietary sources of DHA. Marine microalgae are the primary producers of DHA and the concentration of DHA goes on increasing up in the food chain with these microalgae at the base . Diet and lifestyle issues are closely associated with a myriad of cardiovascular risk factors including abnormal plasma lipid, hypertension, insulin resistance, diabetes, and obesity, suggesting that diet based approaches may be of benefit . Substantial evidence from epidemiological and clinical trial studies indicates consumption of fish; oily fish rich in long chain ω-fatty acids in particular reduce risk of cardiovascular mortality . Low fat intake and associated chronic energy deficiency have been the major nutritional problem of developing countries. The consumption of fat has been found to be lower in developing countries, that is, 49 g/person/day in comparison to 128 g/person/day in the developed countries . It has been observed that the supply of fat and ω-3 fatty acids decreases significantly with decreasing gross domestic product (GDP) and the total ω-3 fatty acid supply is below or close to the lower end of the recommended intake range in some of countries with the lower GDP . Therefore, it is imperative to look for sources of PUFA, particularly DHA and EPA, and other fatty acids for steady supply for health and nutrition of millions of people in the developing countries.
Fish is an important component of human diet in most parts of the world and plays an important role as a source of health friendly fatty acids. The nutrients in fish include PUFA, especially the ω-3 PUFA, DHA, and EPA , proteins, amino acids, and micronutrients (minerals and vitamins). Besides, unlike other animal proteins, fish has the unique advantage that there are many fish species available. Fish is one of the cheapest sources of quality animal proteins and plays a great role in quenching the protein requirement in the developing and under developed countries of the world. Fish is also considered as a health food owing to its oil which is rich in PUFA . The health benefits of fish oil consumption were revealed from the investigations on the Greenland Eskimos  and many such studies to fully explore the health benefits of fish consumption are still being carried out.
Fishes like Salmo salar (salmon), Gadus morhua (cod), and Thunnus thynnus (tuna) serve as the chief sources of DHA and other PUFA in the western countries. However, the Indian subcontinent harbors a rich biodiversity of fishes which markedly varies in their nutrient composition. Therefore, to fully harness the potential of different fish species for human health and nutrition, it is necessary to have comprehensive information of the fatty acid profile of different species of food fishes. In the present study, we report the ω-3 PUFA, DHA, and EPA content, complete fatty acid, and proximate composition of 39 important food fishes from India, which would enhance their utility in public health and nutrition.
2. Materials and Methods
2.1. Ethics Statement
The study including sample collection, experimentation, and sacrifice met the ethical guidelines, including adherence to the legal requirements of the study country. Fresh fishes were collected from the landing stations and were brought to the laboratory in ice. The study did not include any live animal. No specific permissions were required for these locations and activities as these were fish landing centers and are open for customers. The field studies did not involve endangered or protected species.
2.2. Collection of Samples
A total of 39 species of fishes were collected from their landing stations (Table 1). The weight of these fishes ranged between 500 and 800 g per fish except the small indigenous fishes (SIFs) and shellfishes (edible part was taken). Twelve individual fish samples were analyzed in triplicate. For the SIFs and shellfishes, three pooled samples were prepared, each sample containing up to hundred individuals. The length (cm) and weight (g) of individual fish were recorded. Scales were removed by scraping, with the edge of a knife having titanium blade, the blade was rinsed with distilled water, and fillets were removed and freed from bones. The fishes were degutted and muscle fillets were minced and kept in −40°C until usage. For small indigenous fishes, whole fishes were cleaned, descaled, and degutted, and then samples were pooled and minced and kept in −40°C preceding analysis.
|Data previously published by Mohanty et al. .|
Values are reported as mean ± standard deviation.
2.3. Gross Chemical Composition
The gross chemical composition that is moisture, crude fat, crude protein, and ash contents was determined according to AOAC . The minced samples were kept in an oven at °C overnight until constant weight was obtained for moisture estimation. The crude protein and crude fat contents were estimated by Kjeldahl and Soxhlet methods, respectively . Ash content was determined by incinerating known weight of dry sample at high temperature of 600°C for 6 h in a muffle furnace .
2.4. Lipid Extraction and Preparation of Fatty Acid Methyl Esters
Lipid extraction was carried out as per Folch et al. (1957) . In brief, 30 g of minced fish samples was homogenized (using a motor pestle) in the organic solvent mixture (chloroform : methanol, 2 : 1), keeping the solvent/tissue ratio 20 : 1, and filtered applying little vacuum. The extraction and filtration procedure were repeated three times with fresh solvent mixture. The organic fractions, enriched with lipids, were collected, pooled, and dried in a rotary evaporator. The dried lipids were weighed, dissolved in chloroform, and stored in graduated test tubes at 4°C. Fatty acid methyl esters (FAME) were prepared from the extracted fat as per Metcalfe et al. (1966) .
2.5. Fatty Acid Analysis
Fatty acid compositions (oils) of the samples were determined by Gas Chromatography-Ion Trap Mass Spectrometry (GC/IT-MS), Thermo Scientific ITQ 900. Briefly, the FAME was analyzed by injecting 1 μL (30 : 1 split ratio) into GC-MS. The fatty acids were identified and quantified using a GC (Trace GC Ultra, Thermo Scientific) equipped with a capillary column (TR-FAME, 30 m × 0.25 mm, 0.25 μm film thickness) and an MS (ITQ 900, Thermo Scientific) attached to it. For separation of fatty acids, the oven temperature program was set as follows: 1 min initial hold at 50°C, temperature raised from 50 to 150°C at the rate of 20°C per min followed by a hold of 15 min at 150°C, temperature raised from 150 to 240°C at the rate of 20°C per min, and a final hold of 2 min at 240°C. Helium was used as a carrier gas with column flow rate of 1.0 mL per min. The transfer line and ion source temperatures were 250 and 220°C, respectively. The MS conditions were as follows: ionization voltage: 70 eV, range of m/z, and the scan time equal to the GC run time. The individual constituents showed by GC were identified and quantified by comparing the retention times and peak areas to those of standards (ME-14-KT and ME-19-KT, SUPELCO Analytical) and by using the NIST Library (version 2.0, 2008).
2.6. Statistical Methods
All the data are reported as mean ± standard deviation. One-way ANOVA was also employed to compare the variation in fatty acid with respect to different species ().
In the present study, 39 food fishes were selected from different habitats which include 12 in marine water, 3 in brackish water, 14 in freshwater, and 5 in cold water and 3 prawns and 2 mussels considering their commercial importance and consumer preference. Moisture, crude protein, crude fat, and ash contents of the muscle tissue of these fish species are shown in Table 1. The crude fat content showed that, among the species studied, the migratory fish T. ilisha contains the highest amount of fat (10.5%) followed by the marine fish S. longiceps (9.2%) (Table 1). The fish species studied have been further categorized into different groups as lean fish, low fat, medium fat, and high fat according to the fat content  (Table 2). The overview of fatty acid composition of fishes from different habitats is discussed in the following sections (Tables 3–8).