Abstract: In the present study, the fatty acid compositions of golden mullet fillet and roe oil were determined. Palmitic acid (C16:0) was the dominant saturated fatty acid in golden mullet fillet and roe oil with 14.39 and 6.45%, respectively. The major unsaturated fatty acids of golden mullet fillet oil, were detected as palmitoleic acid (C16:1, 17.32%), oleic acid (C18:1, 17.09%) and α-linolenic acid (C18:3, 8.72%). The most abundant unsaturated fatty acids of roe oil were determined as palmitoleic (C16:1, 21.33%), oleic (C18:1, 19.51%), α-linolenic (C18:3, 7.34%), Linoleic acid (C18:2, 6.77%) and docasahexaenoic acid (C22:6, 6.35%). The total unsaturated fatty acids of roe oil (68.59%) were higher than that of golden mullet fillet oil (56.37%). Amounts of ω-3 unsaturated fatty acids in the roe and fillet oil were 19.52 and 14.51%, respectively. Furthermore, the total amounts of eicosapentaenoic acid (C20:5) and docasahexaenoic acid (C22: 6) of roe oil were nearly 2 times higher than those of the golden mullet fillet. Further, the lipid percentage and the amounts of C14:0, C16:0, C18:2, C18:3, C20:5 and C22:6 fatty acids differed significantly (p<0.05) between fillet and roe oil. In addition, significant differences were observed among ω-3 and ω-6 series between both fillet and roe oil.
INTRODUCTION
Golden mullet (Liza aurata) is one of the mullet species which is a coastal migratory fish and important for food and roe. It is a principal economic fish of Caspian Sea and consumers prefer it for nutrition. Especially mullets caught from the Caspian Sea have very delicious taste. Golden mullet usually live in sea and is very durable to ecological factors (as salinity, oxygen, etc.) except cold water.
During the spring and summer, golden mullet migrates to the coastal waters containing abundant food, whereas it migrates to deep waters in winter (Khoroshko, 1981). Its primary foods are zeoplanktons, mollusks larvae, detritus, algae, prephyton and some small aquatics (Belyaeva et al., 1989) on the bed of sea. Spawning period of this fish is comparatively long; from July to September in the Southern Caspian Sea in the depths between 300 to 600 m (Khoroshko, 1981). Its fecundity is 441,000 to 742,000 eggs (Hedayatifard et al., 2002). In Northern of Iran, golden mullet roes are processed by dry salting method and submitted to the local consumer.
Many studies have been conducted on fish flesh and its oil. Fish flesh is composed of high quality proteins and lipids (oil) that are high in monounsaturated and polyunsaturated fatty acids (Ackman, 2005; Exler, 1987).
Fish oil generally contain 20% saturated and 80% unsaturated fatty acids (Chen et al., 1995; Grun et al., 1999; Hedayatifard and Moeini, 2003; Ludorff and Meyer, 1973; Suziki et al., 1986). Fatty acid components of fish oil vary with several factors such as sex, nutrition, catching season, species, maturity, temperature, etc., (Kietzmann et al., 1969; Hedayatifard and Moeini, 2003; Ustun et al., 1996). The caviar is an expensive product with a high nutritional value. Not only the roes of sturgeon fish are the mostly consumed as caviar all over the world, but also the caviar produced from some Caspian Sea fish roes like Liza aurata, Liza saliens, Rutilus frisii kutum and Rutilus rutilus caspicus is partly popular, in Northern provinces of Iran. The fatty acid composition of the roe generally resembles that of the fish flesh oil. There are many studies on the caviar microflora (Altug and Bayrak, 2003; Eun et al., 1994), processing (Hsu and Deng, 1980; Keyvanfar, 1971; Keyvan, 2003; Sengor et al., 2002), proximate composition and identification of roe and caviar of fish species (Chen et al., 1996; Rehbein, 1985).
However, information on the fatty acids of Iranian fish species and roes are lacking. The goal of present study was to investigate the fatty acid compositions of Caspian Sea golden mullet fillet of Iranian origin and its roe oil.
MATERIALS AND METHODS
Sample Preparation
Seventy six golden mullet (Liza aurata Risso, 1810) samples
were obtained from Southern Caspian Sea in October-December, 2006. The
average lengthof golden mullet was 41.75 cm and the average weights of
the fish and its roe were about 0.875 and 0.208 kg, respectively. Prior
to analysis, the fish were gutted and head, tail, fins, viscera and skin
were removed. Fish roes were used as raw caviar. All fish and roe samples
were immediately transferred to the laboratory.
Lipid Extraction and Fatty Acid (FA) Analysis
The fish were filleted and homogenized. Lipids were extracted from the homogenized
edible portion of flesh by the standard AOAC official method 948.15 (Helrich,
1990) using petroleum ether for 6 h in soxhelet extraction apparatus. Lipids
of the roe samples were obtained using the same method after the membrane were
removed from roes. The fatty acid compositions of golden mullet fillet and roe
oil were determined by Capillary Gas Chromatography (CGC) technique. For the
determination of fatty acid composition, the oil samples were converted to their
corresponding methyl esters by BF3-methanol esterification by the AOCS official
method Ce 2-66 (AOCS, 1972).
The fatty acid methyl esters were quantified by gas-liquid chromatography method using a packed column, D.E.G.S -15% and Flame-Ionization Detector (FID) in Simadzo-14 A gas chromatograph (Japan). Helium (99.999% pure) was used as the carrier gas at a flow rate of 45 mL min–1. The detector and injector temperatures were chosen as 210 and 200°C, respectively. The oven temperature was set to 140°C for 5 min and heated to 190°C with a heating rate of 5°C min–1 and the temperature of the oven was also isothermal. Peaks were identified by comparing the retention times with those of a mixture of standard methyl esters (Sigma Chemical Co. Ltd., Poole, UK). All of the other chemicals used in the experiments were analytical grade (Merck, Darmstadt, Germany).
The lipid and fatty acid contents between fillet and roe oil were compared statistically, using t-test and Excel for windows, XP.
RESULTS AND DISCUSSION
The fatty acid compositions of golden mullet and its roe oil are shown in Table 1. In addition, the averages of its fatty acids series are shown in Table 2.
The results showed that palmitic acid (C16:0) was the dominant saturated fatty acid in all samples. The predominance of C16:0, C16:1 and C18:1, fatty acids in golden mullet and its roe may be attributed to the fish diets (Sengor et al., 2003). Fatty acid composition of fish lipid was highly dependent on a number of factors, especially fish diets (Fowler et al., 1994; Karakoltsidis et al., 1995; Okkes et al., 1996; Sathivel et al., 2002).
| Table 1: | Fatty acid composition of Caspian Sea golden mullet fillet and roe oil (Liza aurata) (g/100 g lipid) |
| The data are expressed as the average of three samples. Different letter(s) show significant difference at p<0.05 in fillet and roe oil | |
| Table 2: | Average of fatty acids series in Caspian Sea golden mullet fillet and roe oil (Liza aurata) (g/100 g lipid) |
Levels of palmitoleic (C16:1) and oleic (C18:1) acids of golden mullet fillet oil were 17.32 and 17.09%, respectively. Other unsaturated fatty acid contents of golden mullet fillet oil, such as linoleic (C18:2), α-linolenic (C18:3) and docasahexaenoic (C22.6) were significantly higher than roe oil (p<0.05) with 5.96, 8.72 and 3.55%, respectively. Table 2 shows total lipid contents in roe and the fillet are 10.32±1.33% and 9.25±1.05%, respectively.
Major fatty acids of roe oil were C16:0, C16:1, C18:1, C18:2 C18:3, C20:5 and C22:6. These results agree with the results reported by Lu et al. (1979) and Sengor et al. (2003). They reported that the major saturated and unsaturated fatty acids of gray mullet roe were C16:0, C16:1 and C18:1, respectively. Palmitic acid contents of fillet and roe oil were 14.39 and 6.45%, respectively.
Table 2 shows fatty acids profiles contents of roe oil comparing with those of mullet fillet oil. The total monounsaturated fatty acid contents of mullet fillet and roe oil were 34.41 and 40.48%, respectively.
On the other hand, total polyunsaturated fatty acid contents of mullet fillet and roe oil were 21.96 and 27.75%, respectively.
Regarding to the lipid percentage and the amounts of C14:0, C16:0, C18:2, C18:3, C20:5 and C22:6 fatty acids, there is different significance between the fillet and roe, statistically (p<0.05). The difference between ω-3 and ω-6 unsaturated fatty acids in both fillet and roe oil was also significant, statistically (p<0.05).
Table 2 show total of saturated, unsaturated, mono and polyenoic fatty acids were 22.49, 56.37, 34.41 and 21.96% in fresh fillet, respectively. Also, the mentioned (FA) series were 10.98, 68.59, 40.48 and 27.75% in fish roe oil, respectively.
Total lipid contents in roe were higher than the fillet (Table 2). In addition, rate of ω-3 + ω-6 was 21.96 and 27.75% in fillet and roe oil, respectively. These results defines that golden mullet is one of the best sources for unsaturated oil.
In conclusion, the present study revealed the fatty acid compositions of golden mullet fillet and roe oil in spawning period of golden mullet, which have not previously been studied in Iran. C16:0, C16:1, C18:1, C18:3 and C22:6 were the most abundant fatty acids in fish and roe oil samples. It has been known there is significant seasonality in genders in amount of fatty acid in some fish like Capoeta capoeta umbla (Okkes et al., 1996) and Esox luxius (Hedayatifard and Shabani, 2005). To test this hypothesis, further experiments should be carried out on golden mullet fillet oil of different seasonal periods.
ACKNOWLEDGMENTS
Author thank the Prof. Dr. Amin Keyvan (Islamic Azad University), Prof. Robert G. Ackman (Canadian Institute of Fisheries Technology) and Dr. M. Yousefian (Caspian Sea Ecology Research Center) for their scientific helps. Author thank also the Persia Fisheries Industries Company for their support.