Eur Food Res Technol (2006) 222: 316–320 DOI 10.1007/s0217-005-0040-z
ORIGINAL PAPER
¨ ¨ un ¨ Ozyurt Guls · Abdurrahman Polat
Amino acid and fatty acid composition of wild sea bass (Dicentrarchus labrax): a seasonal differentiation
Received: 8 April 2005 / Revised: 13 May 2005 / Accepted: 20 May 2005 / Published online: 23 September 2005 C Springer-Verlag 2005
Abstract Seasonal variations in the amino acid and fatty acid compositions of wild sea bass (Dicentrarchus labrax) captured in the north eastern Mediterranean were investigated. In all seasons, the major amino acids in sea bass fillets were determined to be aspartic acid, glutamic acid and lysine. Methionine, tyrosine and histidine composition of the fillets were lower than those of the other amino acids in all seasons. The ratios of essential (E, g amino acid/16 g N)/nonessential (NE, g amino acid/16 g N) amino acids were observed to be 0.75 for winter, 0.76 for autumn, 0.77 for both spring and summer. Results showed that, sea bass fillets are well-balanced food source in terms of E/NE ratios in all seasons. In addition, seasonal differences in polyunsaturated fatty acid (PUFA) composition of the fillets were observed in all seasons. The major fatty acids of sea bass fillets were observed to be palmitic acid (16:0), oleic acid (18:1ω9), eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3). The amounts of EPA+DHA in autumn, winter, spring and summer were determined as 0.16, 0.12, 1.14 and 1.02 g/100 g wet weight, respectively. Keywords Dicentrarchus labrax . Seasonal changes . Amino acids . Fatty acids . Proximate composition Introduction The protein quality of food protein depends on its digestibility and its ability to provide all essential amino acids to meet should be supply. It is well known that fish is a perfect protein source. However, the composition of amino acids of fish which is main component of protein are strictly in¨ G. Ozyurt () · A. Polat Department of Fishing and Fish Processing Technology, Faculty of Fisheries, Cukurova University, 01330 Balcali, Adana, Turkey e-mail:
[email protected] Tel.: +90-322-3386084 Fax: +90-322-3386439
fluenced by intrinsic (species, size and sexual maturity) and extrinsic factors (food resources, fishing season, water salinity and temperature) [1–3]. The seasonal changes in water temperature and nutrient are important parameters for composition and quality of fish muscle. It is also known that season has a significant influence on the levels of EPA and DHA of the ω-3 series fatty acids which are the dominant polyunsaturated fatty acids of fish oil [4–9]. These fatty acids have an essential role in human diet in order to prevent diseases and lead a healthy life [10–12]. Fatty acids (ω-3 series) occur in high amounts only in seafood, thus it is necessary to determine their fatty acid compositions. Although the determination of amino acid and fatty acid composition provide necessary information of nutrient value of seafood, deficiency of studies about seasonal variations of these compounds cause difficulty to recommend a suitable preventive diet. Sea bass (Dicentrarchus labrax) is one of the most preferred fish species in Mediterranean countries owing to its desirable aroma and nutritional value. Although there are some researches on the proximate composition and fatty acids in wild and cultured forms of sea bass [8, 13, 14], little information is available on seasonal changes in the amino acids and fatty acids compositions of wild sea bass. There is a requirement to establish the seasonal amino acid and fatty acid profile of sea bass due to its popularity and lack of seasonal information. It is anticipated that the determination of the amino acid and fatty acid composition of wild sea bass will provide the necessary information concerning the nutrient value of this seafood for both to the consumers and to the researchers working on nutrient tables. In addition, this basic information will be obtained for the fish processing industry. Materials and methods Two lots of wild sea bass were captured with longline in the Iskenderun bay, on the north-eastern Mediterranean in February, April, July and November 2001. Twelve individuals for each lot were sampled in
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each season. The mean length and weight of sea bass which age-composition of samples varied from IV to V were 354.18±31.99 g and 31.99±3.0 cm in February, 350.0±54.36 g and 31.83±2.01 cm in April, 351.54±48.19 g and 31.31±1.97 cm in July and 344.18±42.62 g and 31.38±2.37 cm in November, respectively. The fish samples were kept in ice until the fish arrive in the laboratory. After that fish immediately were beheaded, eviscerated and filleted. Proximate compositions were performed in triplicate, while amino acid and fatty acid compositions were done in duplicate. Moisture content was determined in an oven (FN-500, N¨uve, Turkey) at 103◦ C and crude ash was determined in a furnace muffle (MF-120, N¨uve, Turkey) at 550◦ C until the weight became constant. Protein content was determined by AOAC [15] method and lipid content was analysed according to Bligh and Dyer [16] procedures. For amino acid analyses, sea bass samples were hydrolyzed in 6 N HCl under a nitrogen atmosphere for 24 h. The hydrolyzed solution was subjected to Eppendorf LC 3000 (Eppendorf, Germany) automatic amino acid analyzer. The lipids were saponified and esterified for fatty acid analysis by the method of Metcalfe et al. [17]. The fatty acids methyl esters (FAMEs) were separated and quantified with a Hewlett-Packard 5880 gas–liquid chromatograph (GC) using a capillary column equipped with flame ionization detector (FID). Separation was achieved on a 50 m × 0.20 mm i.d. wall-coated open tubular fused silica capillary column coated with Carbowax 20 M. The column, injector, and detector temperatures were maintained at 200 and 300◦ C, respectively. The carrier gas was helium and split ratio of 1:100. Identification was made by comparison to retention times of authentic standards, argentation TLC, followed by GC, of the bands separated by degree of unsaturation, and mass spectrometry. The fatty acids were calculated as a percentage. For conversion of the percentile values to units of weight, the formula recommended by Paul and Southgate were employed [18]. All data obtained separately for each sampling season were subjected to analysis of variance (one-way ANOVA), at 5% confidence level using Duncan [19] multiple range test.
study indicated that the moisture contents in the sea bass fillets in autumn and winter were significantly higher than those of spring and summer (p
