Indian Journal of Geo-Marine Sciences Vol. 42(2), April 2013, pp. 206-210
Seasonal variation in the fatty acid composition of Sardinella longiceps and Sardinella fimbriata: Implications for nutrition and pharmaceutical industry Chitra Som R S* & C K Radhakrishnan Department of Marine Biology, Microbiology & Biochemistry, Cochin University of Science & Technology (CUSAT), Kochi 682 016, India. * [E-mail:
[email protected]] Received 25 July 2011; revised 19 June 2012 Fatty acids of Sardinella longiceps and Sardinella fimbriata of Cochin coast, in four seasonal catches, were profiled and compared. Eicosapentaenoic acid (EPA), and Docosahexaenoic acid (DHA) were the most abundant; EPA dominating in S. longiceps, and DHA in S. fimbriata. Concentrations were also observed to change with season and diet. These variations are complementary, therefore nutritional and pharmaceutical industries using both species in tandem as PUFA sources are expected to be more sustainable round the year. [Keywords: PUFA, EPA, DHA, Seasonal Variation, Sardinella longiceps, Sardinella fimbriata]
Introduction Sardine lipids with their high polyunsaturated fatty acid (PUFA) content are nutritionally important. Omega-3 (n-3) PUFA from Sardines, especially eicosapentaenoic acid (EPA, C-20:5) and docosahexaenoic acid (DHA, C-22:6), are of particular interest because of their role in improving health and reducing the risk of chronic afflictions like cardiac diseases, autoimmune disorders, diabetes, even cancer1. Although the best source of long-chain n-3 PUFA is fish and fish products2,3, fat content and fatty acid profiles change with species, season and diet4,5. Sardines in temperate regions such as Sardinops sagax6, Sardina pilchardus7 and Sardinops melanostictus8 show seasonally fluctuating fatty acid composition and yield, influenced by sea water temperature, food availability and sexual state of the animal. A seasonal examination of S. longiceps in the Indian seas has been carried out envisaging PUFA as a single component9 without analyzing the granularity of individual fatty acids. A catalogue of the fatty acid compositions of 31 marine species, including S. longiceps and S. fimbriata, for a single sampling period has been published10.Both fishes are among the cheapest and most abundant along Cochin coast; S. longiceps is mostly consumed by the inhabitants11, while S. fimbriata with its bony flesh is unpopular and less in demand than its congener. It has been postulated that EPA and DHA originate in unicellular phytoplankton and seaweeds and once
incorporated into the lipids of fish that consume the algae, they are passed on through food chain to other species2. Though phylogenetically close, the feeding patterns of the two Sardines are different: S. longiceps favours a phytoplankton diet12 while S. fimbriata prefers zooplanktons13. Consequently, the fatty acid profiles of the fishes are also expected to be mismatched. Present study compare fatty acid compositions of S. fimbriata and S. longiceps through four seasons, with special attention to seasonal fluctuations and inter-species differences in their EPA and DHA content. Commercial ramifications of the deviations, for nutritional and pharmaceutical endeavors to extract DHA and EPA from these two species, have been noted. The study also enumerates the reasons for these variations across seasons and species. Materials and Methods Sampling was done on the 15th day of four months representative of the four Indian tropical seasons14 – September (post-monsoon), December (winter), March (summer) and June (monsoon). Fresh specimens of S. longiceps and S. fimbriata, were collected from the Kaalamukku landing centre (9°58’55’’N, 76°14’33’’E) at Kochi. Samples washed in sterile water were kept in ice boxes and brought to the laboratory within 30 minutes. Fishes were identified for their maturity periods15, their lengths measured and stomach content analyzed16. Details are provided in Table 1.
SOM & RADHAKRISHNAN: SEASONAL VARIATION IN THE FATTY ACID COMPOSITION OF SARDINELLA
207
Table 1—Sampling Details Season
Notes on Catches and Sampling
September
Mostly Running (6) or Partially spent ones (7a) in the catch. Rarely Immatures (1). Selected samples were in stage 6. Mostly immatures (1) and rarely Spent (7b) or Spent Resting (2b). Selected samples were in stage 1. Mostly immatures (1) and developing virgin (2a) stages. Selected samples had both 1 and 2a stages Mostly maturing (4) and sometimes mature (5). Selected samples were in stage 4
December March June
Lipid content of the tissue was estimated by the method of Folch et al.17. Fatty acids were analyzed by converting them into volatile methyl esters according to the method of AOAC18. These methyl esters of fatty acids (FAME) were separated by gas liquid chromatography equipped with a capillary column and a flame ionization detector. Separated fatty acids were identified by comparison of their retention times with those of standards. Measurement of peak areas and data processing were carried out by Thremo Chrom card software. Individual fatty acids were expressed in mg/gm meat tissue - a measure of absolute yield. The same values were also expressed as percentage of total FA/PUFA and compared. Industrially, this relative yield is an index of the quality of products obtained from the fish. Important fatty acids, and aggregates like Saturated Fatty Acids (SFA), Mono-unsaturated Fatty Acids (MUFA) and PUFA were systematically scrutinized. Results S. longiceps has a higher concentration of all three variants of FA across the four seasons (Fig. 1). For both species FA concentration is highest in December (165.71 mg/g and 90.38 mg/g), but it is lowest during June and September In both species PUFA dominate the profile, followed by SFA and MUFA (Figs 2 & 3). Corresponding to FA surges, concentration of PUFA peaks during winter (December-March) and drops during spawning season (June-September). Of the 31 identified FA in the Sardines, seasonal trend of seven dominant FA is shown (Table 2). Palmitic Acid (C:16) is the dominant SFA in both species followed by Tetradecanoic Acid (C14) and Stearic Acid (C18) respectively. Palmitic Acid (C:16) has no noticeable trend across seasons, Among MUFA, Oleic Acid (C18:1n-9) was the most dominant followed by Palmitoleic Acid (C16:1).
S. longiceps (length in mm) 178.8±5.11
S. fimbriata (length in mm) 142.6±3.91
131.4±3.13
105.2±5.71
138.6±5.85
111.2±10.63
165.6±7.3
129.2±5.54
Fig. 1—Fatty Acid Profile of two Sardines
Fig. 2—Seasonal trend of various types of fatty acids present in Sardinella longiceps
Fig. 3—Seasonal trend of various types of fatty acids present in Sardinella fimbriata
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Table 2—Trend of important fatty acids across seasons In percentage of total fatty acids Sardinella longiceps Sardinella fimbriata Dec Mar June Avg Sept Dec Mar June
FA
FA Name
Sept
C14
Tetradecanoic Acid
10.93
12.33
7.68
13.18
11.03
4.62
7.77
3.94
6.43
5.69
C16
Palmitic Acid
17.14
15.63
21.87
16.68
17.83
22.81
14.58
15.43
19.46
18.07
C16:1
Palmitoleic Acid
7.40
2.41
8.30
5.53
5.91
3.14
3.93
7.58
2.41
4.27
C18
Stearic Acid
7.85
5.31
6.19
5.97
6.33
11.90
4.76
7.25
9.66
8.39
C18:1n-9
Oleic Acid
18.30
14.18
8.99
19.20
15.17
4.15
5.32
7.74
7.02
6.06
C20:5n-3
Eicosapentaenoic Acid
22.39
22.98
19.96
21.72
21.77
8.26
14.43
18.23
6.94
11.96
C22:6n-3
Avg
Docosahexaenoic Acid
6.86
14.88
18.42
6.22
11.59
31.27
37.26
31.82
32.02
33.09
Σ SFA
38.33
35.43
36.35
39.30
37.35
43.87
29.56
29.12
40.44
35.75
Σ MUFA
25.91
16.75
17.79
25.15
21.40
7.47
9.97
15.55
9.56
10.64
Σ PUFA
33.77
46.35
44.08
34.22
39.61
46.16
58.45
53.30
48.69
51.65
% EPA in PUFA
66.31
49.59
45.29
63.47
54.95
17.89
24.69
34.19
14.25
23.16
% DHA in PUFA
20.32
32.10
41.78
18.17
29.27
67.75
63.75
59.70
65.77
64.07
Fig. 4—Variations in EPA and DHA in Sardinella longiceps
Fig. 6—Variation in EPA concentration of two Sardines
Fig. 5—Variations in EPA and DHA in Sardinella fimbriata Fig. 7—Variation in DHA concentration of two Sardines
EPA was the dominant PUFA in S. longiceps while DHA showed dominance in S. fimbriata. Relative concentrations of EPA and DHA with respect to total PUFA varies much across seasons in both Sardines (Figs 4 & 5). June and September showed a higher concentration of EPA and lower concentrations of DHA in S. longiceps. During the same months, DHA is higher in S. fimbriata. In both species, the DHA-EPA concentrations show an inverse relationship – when DHA values are less, EPA values is more and vice versa. Between
the species too, EPA and DHA values are complementary – when EPA values of S. longiceps are high, they are low for S. fimbriata and vice versa; the same holds good for DHA too (Figs 6 & 7). Bray-Crutis analysis of similarity indices for both species indicates two clusters in terms of fatty acid variations (Figs 8 & 9). Fatty acid composition during spawning period (June-September) seems to be more similar and divergent from the winter (March–December).
SOM & RADHAKRISHNAN: SEASONAL VARIATION IN THE FATTY ACID COMPOSITION OF SARDINELLA
Fig. 8—Bray-Crutis similarity index for FA from Sardinella longiceps
Fig. 9—Bray-Crutis similarity index for FA from Sardinella fimbriata
Discussion The higher concentration of FA in December, compared to that in June and September in both the fish species coincides with their spawning period19,20. A similar trend in Cornish mackerel has been attributed to fat mobilization associated with gametogenesis21. Also, during winter, sea water temperature falls from 30-31°C to 25-26 °C and fishes like sardines increase their FA content to survive the lower temperature. An identical observation has been made in Sardines elsewhere6,7,8 including S. longiceps in the tropic coasts9. Yet another reason could be the dominance of juveniles and immatures in the catch during winter, when these heavy feeders accumulate large quantities of fat. The escalating FA and PUFA concentrations in winter allow greater PUFA intake per sardine. The yield from an industrial production unit will also be higher and more profitable during winter. In June-Septemeber, MUFA registers a complementary increase in both species. This inverse relation has been noted in a variety of other fishes along the west coast10; however its biochemical implications are unknown.
209
Palmitic Acid, the dominant SFA in both the species, showed no noticeable variations across the seasons, which appears to be true for other species of Sardines as well8. This compound is hypothesized as not influenced by diet22,23. With respect to MUFA, our studies agree with prior findings2 that the main MUFA detected in marine lipids usually contains 18 carbon atoms. The mismatched DHA-EPA profiles of these Sardines make a classic model for trophic upgradation in the seas. Zooplanktons, the main food source of S. fimbriata, feed on microplanktons – and the microplanktons in turn feed on phytoplankton which is the chief food of S. longiceps. These microplanktons, also known as heterotrophic protists, trophically improve algal quality for consumption by higher trophic organisms21. As an intermediate prey, they improve the quality and quantity of lipids in the food web by forming fatty acids like DHA with higher levels of unsaturation24. The greater concentration of DHA in zooplankton is a consequence of this preferential assimilation in planktonic food webs by microplanktons. Zooplankton-feeding S. fimbriata are therefore essential in nutrition, and food products based on this species will optimize DHA intake. This also encourages pharmaceutical enterprises to base their operations on S. fimbriata for DHA-rich drugs, while veering closer to S. longiceps as an ideal source of products loaded with EPA. Relative concentrations of EPA and DHA to that of total PUFA shows seasonal variations across seasons. This complementary trend can be explained by the maturity stage prevalent in the catch, and dietary patterns as confirmed by analysis of stomach content. June-September is characterized by the presence of spawning adults of S. longiceps. They are exclusive phytoplankton feeders11 and hence have an EPA-rich diet. But the immatures found abundantly in winter are carnivorous with varying amounts of zooplankton entering their diet. Owing to their well-formed gillrakers adult S. longiceps are capable of efficiently sieving minute phytoplanktons; on the other hand the under-developed gill-rakers of the immatures permit larger zooplanktons25. This diet increases the DHA content in S. longiceps catch during winter. Conversely the adults of S. fimbriata found during June-September are exclusive zooplankton feeders12 and have high DHA content. But the immatures found during December-March eat varying amount of phytoplankton also26 raising the EPA levels in winter.
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The inverse relationship of DHA-EPA concentration between the species, from an industrial perspective, means that while the quality of PUFA extract from any single species will vacillate with seasons, a steady, round the year production of EPA or DHA can be maintained by installing well-thoughtout measures, utilizing both species. Despite variations in the yield, the high degree of similarity (>50%) in the fatty acid profile across seasons is encouraging as it provides a minimum assurance on the levels of various individual fatty acids present in the extract through out the year.
7
Conclusion The two dominant Sardines of Cochin coast are an excellent source of essential fatty acids, especially EPA and DHA. EPA dominates in S. longiceps and though less-favored, S. fimbriata is the richer source of DHA. In both species, strong variation in FA profiles exists between spawning and winter seasons, attributed to food habits, lifecycle stages, and sea water temperature. Complementary PUFA profiles of the sardines are well-suited for food and pharmaceutical industries generating PUFA-enriched foods or specialized drugs, and this comprehensive knowledge will help design better processes for consistent yield throughout the year, using both species.
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8
9
10 11
14 15 16
17 18 19
Acknowledgement Authors are thankful to the authorities of Cochin University of Science and Technology for facilities and financial help. References 1 2
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