Iranian Journal of Fisheries Sciences 10(1) 67-74 2011

Seasonal variation in chemical composition of the Indian mackerel (Rastrelliger kanagurta) from Karachi Coast

Nisa, K. ; Asadullah, K. *

Received: April 2009 Accepted: January 2010

Abstract The chemical composition variations of the Indian mackerel (Rastrelliger kanagurta) from Karachi coast were investigated seasonally over the period of one year (2004-2005). Moisture, crude protein, fat and ash contents varied from 70.11-74.41%, 16.02- 20.09%, 3.0- 12%, and 0.89-1.35% respectively. The seasonal data indicated that the main fatty acids of the total lipid were C16:0, C16:1, C18:0, C18:1, C20:5 and C22:6. Total contents of saturated fatty acid (SFA), monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) percentages varied from 31.6-46.85%, 20.5-27.9%, and 26.8-40.85% respectively. Eicosapentaenoic acid (EPA, C20: 5n-3) and docosahexaenoic acid (DHA, C22: 6n-3) of omega 3 series which have specific importance in nutritional values concept, were the major fatty acids. The lowest EPA and DHA were found to be in July and highest in November to March.

Downloaded from jifro.ir at 19:15 +0330 on Wednesday September 29th 2021 Keywords: Chemical composition, Seasonal variation, Fatty acid, Rastrelliger kanagurta

______-Food and Marine Resources Research Center, PCSIR Laboratories Complex Karachi,Shahrah-e-Dr. Salimuzzaman Siddiqui, Off University Road Karachi, Pakistan. *Corresponding author's email: [email protected] 68 Nisa & Asadullah, Seasonal variation in chemical composition of the Indian mackerel….

Introduction Marine food especially fish are an Karachi coast has been expressed in important part of the human diet across the previous studies (Nisa et al., 1996; Nisa et world. Nutritional importance of fish is al., 2001; Nisa and Asadullah, 2006) and well documented and consumption is recently seasonal changes in lipid associated with not only protein and composition in sardines from the same minerals but also largely with omega-3- region have been studied (Nisa and polyunsaturated fatty acid (PUFA) content Asadullah, 2008). However, no (Ackman, 1989). Owing to its numerous information is available on seasonal beneficial effects of omega-3-PUFA on variation in fatty acids of this species of human health, the nutritional content of mackerel. Mackerel are commercially fish has extensively been studied in the last important fish of the coastal area of decades. Seafood lipids are the best natural Pakistan and the total catch during 2003 source of highly unsaturated fatty acid and was 31126 metric ton (Hand Book of are the major contributor of omega-3- Fisheries statistics of Pakistan). The Indian PUFA, particularly eicosapentaenoic acid mackerel (Restrelliger kanagurta) is (EPA, C20: 5n-3) and docosahexaenoic commonly harvested throughout shallow acid (DHA, C22: 6n-3). They provide a waters of Pakistani coastal area (Moazzum broad range of health benefits which are et al., 2005). not found in any other fat (Ackman et al., The aim of the present study was to 1974; Dyerberg and Bang, 1979; Kromann determine the best time of year in which and Green, 1980; Hoope et al., 2006; fish have eminent nutritional components Harris, 2007). It has been found that omega especially protein and omega 3 PUFA 3 PUFAs has a great contribution against particularly EPA and DHA. heart and tissue related diseases. They have beneficial effects on hypertension, Materials and methods diabetes, macular degeneration etc. and Mackerel samples were obtained from

Downloaded from jifro.ir at 19:15 +0330 on Wednesday September 29th 2021 that its deficiency results in disorders such Karachi fish harbor, during the period May as skin diseases anemia and defect in 2004 to April 2005, packed in ice for eyesight (Mehmet, 2008). Therefore the transport to the laboratory. The fish were fat content and fatty acid composition is washed with deionized water and stored at important when utilization of fish species -40 oC until analyzed. Prior to analysis, fish is considered. were thawed at room temperature and were It is generally known that marine filleted. In order to determine the total lipid fish have seasonal variations in chemical composite, 100 g sample weighed was composition especially in fatty acids. homogenized for 2 minutes with a mixture These variations are correlated generally of 100 ml chloroform and 200 ml with the environmental factors like methanol. 100 ml chloroform was added to temperature salinity, composition of their the mixture and after homogenizing for 30 food as well as activities (reproduction and seconds, 100ml distilled water was added migration) including age, sex and size of and homogenized for further 30 seconds. fish (Standby 1981, 1986; Ackman, 1982). The homogenate was filtered and Data on proximate composition and fatty transferred to the separating funnel for acid profile in fish and shellfish from complete separation of two layers. The Iranian Journal of Fisheries Sciences, 10(1), 2011 69

chloroform layer was removed and 0.05), highest in December and lowest in evaporated to dry in a rotary evaporator January and June. Crude protein varied (Bligh and Dyer, 1959). In order to prevent from 16.65% to 20.09%, highest in June oxidation, lipid was stored under nitrogen and lowest in December. Moisture content

(N2) in a screw caped test tube for further varied from 70.11% to 74.41%, highest in analysis at freezing temperature. The May and lowest in December. The ash moisture, ash and protein content of fish content varied from 0.89% to 1.35%, were determined as described by AOAC highest in March and lowest in December. (1984). The protein content was calculated Table 2 presents seasonal variations in by converting the nitrogen content fatty acid composition. determined by Kjeldhl method (6.25 x N). The total saturated fatty acid (SFA) All three composite samples were used in varied from 31.6% to 46.85% (p< 0.05), this study. highest in July and lowest in February. The preparation of the fatty acid Among the SFA, Palmitic acid (C16: 0) methyl esters (FAME) from the total lipid varied from 23.0% to 32.0% (p< 0.05), was carried out by saponification and highest in August and lowest in March. methyl esterification by Christie (1989). Amongst the unsaturated fatty acids, total The fatty acids compositions were then MUFA showed a slight decrease in the determined by using chrompack CP 9001 month of May, June and July and an gas chromatography, equipped with a polar increase in November and December. The 50 m capillary column, BP x 70 (SGE total MUFA content varied from 20.5 % to Australia, 50 m x 0.32 ID, 0.25 um layer 27.9% (p< 0.05). The prominent MUFA thickness) with hydrogen FID and using was C18:1 which varied from 11.2% to helium as carrier gas. The oven was 13.0 % and was lowest in February and programmed to rise from the initial reached the maximum content in temperature of 85 oC to 150 oC at a rate of December. C16: 1 was the next prominent 30 oC /min, from 150 oC to 152 oC at 0.1% MUFA, varying from 3.5% to 6.2%, lowest o o o

Downloaded from jifro.ir at 19:15 +0330 on Wednesday September 29th 2021 /min, from 152 C to 172 C at 0.65 C in September and highest in December. /min, from 172 oC to 187 oC at 25% /min The seasonal changes of total PUFA were and stayed at 187 oC for 7 min. The injector quite distinct being the major group was heated from 85 oC to 190 oC at 5 oC / attaining the lowest value in July, 23.97% sec and stayed at 190 oC for 30 min. The and highest in February, 40.85%. The internal standard used was C20: 2(n-6) and omega-3 fatty acid series, EPA and DHA individual FAME was identified as a which were dominant PUFA , showed relative percentage of comparison with some variation during the study year, EPA authentic standard reference mixture (Nu- varied from 7.5% to 13.0% (p< 0.05), chek-prep.Inc; USA). lowest in August and started to increase from September and reached its maximum Results in January and February. Whereas the The chemical composition of mackerel was DHA ranges were from 10.0% to 16.8% determined over the period of one year and (p< 0.05), minimum in July and maximum the results obtained are present in table 1. in November, December, January and Fat content varied from 3.0% to 12.0% (p< February.

70 Nisa & Asadullah, Seasonal variation in chemical composition of the Indian mackerel….

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Discussion Seasonal data showed that even though fat same results were showed in other studies content is somewhat high in the present carried out by Bandarra et al. (2001, 1997), study but the variation trend was to some Kostas (2007) and Spiros and Mehmet extent in agreement with the values of (2008).The saturated fatty acid (SFA) Bandara et al. (2001) for the Indian horse varied from 31.6% to 46.85% (p< 0.05), mackerel. According to Borges and Gordo highest in July and lowest in February. The (1991) the spawning season of this species amount of SFA was not only in agreement takes place during the first semester of the with the findings of Spiros and Kostas year, which would be the probable reason (2007) and Mehmet (2008) but also with of low fat content in this time of year. the previous study on sardine (Nisa and Protein percent reached its Asadullah, 2008). Amid the SFA, Palmitic maximum in June and minimum in acid (C16: 0) was the major fatty acid December. Low protein in this month may which showed seasonal variation like the suggest that protein may utilize for one reported by Ackman (1964), Ackman metabolic energy. The recorded values for and Eaton (1966) and Bandarra et al. crude protein were not only in agreement (2001) and reported similar findings and with the values of Bandara et al. (2001) but concluded that C16: 0 was a key metabolite also to some extent with findings of in fish and did not seem to be influenced Mehmet (2008) for mackerel species. by diet. The recorded results for moisture MUFA content in the present study were somehow in agreement with the was comparatively high, however the findings of Soyer and Sahin (1999) for seasonal variation trend (Table 2) was not chud mackerel. However Aubourg et al. only somehow in agreement with the (2002), Aubourg and Uglianol (2002) and findings of the previous study (Nisa and Losada et al. (2005) identified moisture Asadullah, 2008) but also with the findings

Downloaded from jifro.ir at 19:15 +0330 on Wednesday September 29th 2021 contents in horse mackerel as 75% to 79%, of Bandarra et al. (2001). Amongst the 78.2% and 77-81% respectively. The ash MUFA, high level of C18:1 was in content varied from 0.89% to 1.35%, accordance with findings by Ackman highest in March and lowest in December. (1982) who pointed out that the main These findings were in agreement with MUFA in marine lipid usually contained Mehmet (2008), as ash content of the under 18 carbon atoms. studied species was high in March (spring). The seasonal changes of total The seasonal data on sardines indicated PUFA had a considerable effect on the that the main fatty acids C16: 0, C18: 0, variation of unsaturated fatty acid content, C16: 1, C18: 1, C20: 4, C20: 5, C22: 6 from season to season which may suggest were common in all the seasons but their that PUFA may be responsible for the compositional percentage varied widely seasonal variation of total unsaturated fatty through out the year. These major fatty acids. The dominant PUFA are those of acids were not only same as the previous the omega-3-series, found chiefly were study on sardines from the same region EPA and DHA of therapeutic importance (Nisa and Asadullah, 2008) but also the (Sanders et al., 1997; Montori et al, 2002), 72 Nisa & Asadullah, Seasonal variation in chemical composition of the Indian mackerel….

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