International Journal of Aquatic Biology (2014) 2(5): 223-228 E-ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.NPAJournals.com © 2013 NPAJournals. All rights reserved Original Article Effect of different cooking processes on the fatty acid profile of grass carp (Ctenopharyngodon idella) fillets during chill storage Ensieh Hayati-Jafar Beigi1, Ebrahim Alizadeh1*,1Eshagh Zakipour Rahimabadi1, Mostafa Yousef Elahi2 1Department of Fisheries, Faculty of Natural Resources, University of Zabol, Zabol 98615-538, Iran. 2Department of Animal Science, Faculty of Agriculture, University of Zabol, Zabol 98615-538, Iran. Article history: Received 29 May 2014 Accepted 23 September 2014 Available online 2 5 October 2014 Keywords: Grass carp Fatty acid Cooking Chill storage Abstract: The effects of different cooking methods (deep fat frying, boiling and steaming) on lipid content and fatty acid composition of grass carp (Ctenopharyngodon idella) fillets during chill storage were investigated. Fillet samples were cooked and then stored at + 4°C for 4 days. The control and the cooked fillet samples were analyzed for their chemical characteristics. Twelve fatty acids were identified with 39.11, 15.37 and 45.52 g/ 100 g of saturated (SFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), respectively. The n-3/n-6 ratios of raw, deep fried, boiled and steamed samples were 1.12, 0.10, 1.45 and 0.72, respectively. The pattern of changes in fatty acid groups was different in fried, boiled and steamed samples after 1 and 4 days of chill storage. The EPA+DHA/C:16 ratio was higher in boiled and boiled-chill stored samples than steamed and fried samples. EPA+DHA/C:16 ratio for cooked, stored for 1 day and then 4 days were as 0.051, 0.003 and 0.017 for fried, 0.492, 0.583 and 0.489 for boiled and 0.247, 0.037 and 0.149 for steamed samples, respectively. These results showed that the boiled process is better than other cooking processes on the FA pattern of grass cap. Introduction Different aspects of beneficial effects of fish lipid on human health have been widely established (Arts et al., 2001; Connor, 2000) because of its long chain polyunsaturated fatty acids of n-3. Various environmental and biological factors and different processing method can effect on the content of lipid and composition of fatty acids of fish species (Sigurgisladóttir and Pálmadóttir, 1993; Love, 1997). It is well-known that changes in lipid content and fatty acid composition in frying process are higher than other cooking processes (Gladyshev et al., 2006; Gladyshev et al., 2007; Bakar et al., 2008; Larsen et al., 2010). Therefore, the pattern changes of long chain polyunsaturated omega-3 fatty acids are different based on fish species and cooking procedure (García-Arias et al., 2003; Gladyshev et * Corresponding author: Ebrahim Alizadeh E-mail address: ebi_alizadeh2003@yahoo.com al., 2007; Bakar et al., 2008; Larsen et al., 2010; Nikoo et al., 2010a). The cooking process, chill storage and reheating is a common practice in large catering operations, restaurants, and homes (Bakar et al., 2008). The changes in lipid content and fatty acid composition have studied in cook-chill-reheat or cook-freeze- reheat by García-Arias et al. (2003), Bakar et al. (2008) and Nikoo et al. (2010a, b). Although there are many references regarding the effects of cooking on fish fatty acid composition, data related to the effect of cooking and chill storage on fatty acid composition and lipid content of grass carp (Ctenopharyngodon idella) is limited. Therefore, this research was aimed to study the effects of different cooking processes on lipid content and fatty acid profile of grass carp fillets during chill storage. 224 International Journal of Aquatic Biology (2014) 2(5): 223-228 Materials and methods Sample preparation: Twenty fresh grass carp with weight of about 1.5 kg were purchased from a local market (Zabol, Iran). They were transported in isothermal iceboxes to the laboratory 5 hrs after catching. Then, they were cleaned and filleted and same weight of fillets (about 100 g) were used for cooking process (deep fat frying, boiling and steaming). The cooked samples were placed in moisture-impermeable plastic bags, stored in chill room (+4°C) and analyzed on 0, 1 and 4 days. The experiences were performed with three replicates. Cooking process: Fish fillets were fried in frying oil (Sunflower oil, Bahar, Iran) using a deep fryer (Aaura, Tefal, Iran) for 6-7 min which was preheated to 180ºC. The fillets were boiled in a small water under 85-90ºC for 10-15 min (Gladyshev et al., 2006). For steaming, samples were placed in a steamer (Panasonic, Japan) and steamed for 5–6 min. After cooking all samples were drained gently on a stainless steel grills and air cooled. Chemical analysis: Soxhlet apparatus with diethyl ether as solvent was used to measuring the total lipid content (AOAC, 2000) and lipid extraction was performed based on Bakar et al. (2008). Lipid samples were converted to their constituent fatty acid methyl esters according to Metcalf et al. (1966). Analysis of fatty acid methyl esters was performed by a Unicam 4600 with a bpx 70 capillary column (30.0 m X 0.25 mm i.d.) and quantified by FID detector. The split ratio was 10:1. The GC condition was as follows: injection port temperature was 300ºC and FID temperature was 350ºC. Oven temperature program was set at an initial temperature of 160ºC for 6 min, then raised to 180ºC at 20ºC min-1 and held for 9 min and again was raised to 190ºC at 20ºC min- 1 and held for 14 min (Metcalf et al., 1966). The carrier gas was helium. The column flow rate was 1.9 mL min-1. In the detector, helium gas flow rate was 30 mL min-1. The sample size was 1 μL. Statistical analysis: The data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey’s test. The significance of results was at 5%. All data are expressed as mean ± S.D. Results The total lipid content of raw grass carp fillet was 1.44% (based on wet weight). Deep frying significantly (P<0.05) increased the fillet lipid content to 26.7%. There was slight increase in lipid content of boiled and steamed samples (Table 1). The fatty acid composition of raw samples is shown in Table 2. Twelve fatty acids were identified with 39.11, 15.37 and 45.52 g/100 g of saturated (SFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), respectively. In raw samples, the abundance of fatty acids (in decreasing order) were palmitic acid (C16:0, with 29.27 %), oleic acid (C18:1 n-9, with 14.65 %), linoleic acid (C18:2 n-6, with 12.44 %), docosahexaenoic acid (C22:6 n-3, with 9.20 %) and Arachidonic acid (C20:4 n-6, with 9.02 %). N-3 and n-6 fatty acids constitute about 52.06 and 47.14 % of PUFAs, respectively, exhibiting an n-3/ n-6 ratio of 1.12. The abundance of fatty acid groups (in decreasing order) in fried, boiled and steamed samples were MUFAs > PUFAs > SFAs, PUFAs > SFAs > MUFAs similar to raw samples and MUFAs > SFAs > PUFAs, respectively (Table 3). In boiled samples, content of higher polyunsaturated fatty acids was decreased, while C18:3 (n-3) significantly increased (P<0.05). The patterns of changes in fatty acid groups was different in fried, boiled and steamed samples after 1 and 4 days of chill storage (Table 3). After 1-day storage of fried samples, the SFAs levels were increased significantly (P<0.05), samples Raw Cooked Deep fried Boiled Steamed Lipid content (%) 1.44 26.7 1.94 1.94 Table 1. Lipid content of raw and cooked of grass carp fillets (% basis on wet weight) 225 Hayati-Jafar Beigi et al/ effect of different cooking processes on the fatty acid profile of grass carp whereas slight decrease were observed in MUFAs and PUFAs. A significant increase were found in MUFAs levels of boiled samples after 1 days of storage (P<0.05), while the content of PUFAs were significantly decreased (P<0.05) (Table 3). Longer storage of steamed samples in chill room was led to little increase in SFAs, significant increase in MUFAs and also significant decrease in PUFAs, respectively (P<0.05) (Table 3). Discussion The average lipid content of raw samples in this study was slightly less than the values reported by Wu and Mao (2008) and Ojagh et al. (2009) for grass carp. Among the biological and environmental factors, diet has a great effect on the lipid content of fish flesh (Sigurgisladóttir and Pálmadóttir, 1993). Based on the classification by Suriah et al. (1995), grass carp may be classified as lean fish with lipid content below 5%. After frying, fat content of fillet samples significantly (P<0.05) increased. This result is in agreement with those of Garcia-Arias et al. (2003), Gokoglu et al. (2004), Weber et al. (2008) and Hakimeh et al. (2010), although the value obtained in this study was higher. The increase of total lipid Table 2. Fatty acid composition of grass carp fillets changes after cooking and chill storage. Values are mean ± standard deviation of two determinations. Capital letters (A, B, C) in the same line indicate significant differences (P<0.05) of storage. Small letters (a, b, c, d, e) in the same line indicate significant differences (P<0.05) of treatment. Fatty acid (g/100 g fatty acids) Raw fillet Fried samples Boiled samples Steamed samples Day 0 Day 1 Day 4 Day 0 Day 1 Day 4 Day 0 Day 1 Day 4 ∑ SFA 39.112 30.300 33.774 31.233 32.443 32.940 34.887 33.662 32.939 33.992 ∑ MUFA 15.370 35.576 33.267 32.919 17.767 39.613 39.263 41.729 32.373 35.441 ∑ PUFA 45.517 34.125 32.959 35.848 49.790 27.447 25.850 24.610 34.689 30.567 ∑ n-3 24.061 3.211 1.855 3.151 29.450 19.335 19.498 10.288 4.515 11.749 ∑ n-6 21.456 30.914 31.104 32.697 20.340 8.112 6.352 14.322 30.174 18.818 n-3/ n-6 1.121 0.104 0.060 0.096 1.448 2.380 3.069 0.718 0.150 0.624 Table 3. Changes in fatty acid groups of grass carp fillets after cooking and chill storage. 226 International Journal of Aquatic Biology (2014) 2(5): 223-228 content was not significant in boiled and steamed samples. Similar findings have reported by Weber et al. (2008) and Gokoglu et al. (2004) for boiling and by Hakimeh et al. (2010) for steaming. Cooking induces water loss in the food, which in turn increases its lipid content (Hoffman et al., 1994; García-Arias et al., 2003). Fat increase in fried sample could be due to oil penetration into the food after water is partially lost by evaporation. Ågren and Hänninen (1993) have concluded that additional oil in frying, mainly determines the small and lean fish lipid content. The fatty acid profile in this study was similar to that found by Ojagh et al. (2009) and Wu and Mao (2008) for grass carp, although in present study, the content of PUFAs and MUFAs were higher and lower, respectively. Based on the results, the content of C18:1 n-9c and C18:2 n-6c increased significantly after frying, while the content of other fatty acids decreased, especially docosahexaenoic acid and Arachidonic acid. García- Arias et al. (2003) and Bakar et al. (2008) reported similar observations for shallow fat frying where the cooking process had significantly affected the fatty acid composition of fish, increasing oleic and linoleic acids and decreasing eicosapentaenoic and docosahexaenoic acids. It has reported that fatty acid profiles of fish in frying processes became similar to those of the culinary fat used (Arias et al., 2003; Bakar et al., 2008). The saturated fatty acid content decreased significantly in boiled samples. This could be explained by the fact that SFAs are largely represented in neutral lipids and are more prone to migration (Enser et al., 1996; Badiani et al., 2002). In steamed samples, higher polyunsaturated fatty acid content decreased significantly, whereas the content of C18:1 (n-9) was increased. This finding is not in agreement with finding of Bakar et al. (2008) and Larsen et al. (2010) who reported no differences between steamed and raw samples. The n-3/n-6 ratio of deep fried, boiled and steamed samples were 0.10, 1.45 and 0.72, respectively. The longer storage of fried samples in chill room was caused a slight decrease in SFAs and MUFAs and slight increase in PUFAs. The changes in fatty acid profile during storage in chill room could be due to changes in SFA and MUFA content which are neutral lipids and more prone to migration (Enser et al., 1996; Badiani et al., 2002) and also oxidation progress during storage (Bakar et al., 2008; Nikoo et al., 2010a). The SFAs levels increased after 4 days of storage of boiled samples, while the levels of PUFAs decreased. Nikoo et al. (2010b) observed that the content of polyunsaturated fatty acids of Rutilus frisii kutum decrease, whereas the content of saturated fatty acids increased after 2 days of refrigerated storage. A significant decrease and increase of MUFAs and PUFAs were observed for the steamed King Mackerel after 1-day of storage, respectively, while the decrease of SFAs was not significant (Bakar et al., 2008). Nutritional value of lipids is determined not only by the composition of fatty acids, but also by their ratio (Simopoulos, 1999; Schmitz and Ecker, 2008). Imbalance in the ratio of n-6 and n-3 acids (which should be about 3-5:1) can contribute to the development of cancer and the various kinds of inflammation (El-Badry et al., 2007). This research demonstrates that, the n-3/n-6 ratio decreased to 0.060 and then increased to 0.096 after 1 and 4 days of storage in fried samples. This ratio increased to 2.380 and 3.069 after 1 and 4 days of storage in boiled samples. In steamed samples, n-3/n-6 ratio decreased to 0.150 and then increased to 0.624, respectively. These results indicate that the fatty acid composition of fried sample was affected by the frying oil agreeing with previous studies (Amira et al., 2010; Kitson et al., 2009). The EPA+DHA/C:16 ratio was higher in boiled and boiled- chill stored samples than steamed and fried samples. EPA+DHA/C:16 ratio of cooked, stored for 1 day and then 4 days were 0.051, 0.003 and 0.017 for fried samples, 0.492, 0.583 and 0.489 for boiled samples and 0.247, 0.037 and 0.149 for steamed 227 Hayati-Jafar Beigi et al/ effect of different cooking processes on the fatty acid profile of grass carp sample, respectively. Some researchers reported that there was a significant effect of frying on the EPA and DHA levels in fried fish (Özogul et al., 2009; Gladyshev et al., 2006). The decrease in the EPA and DHA levels after frying may have been resulted from susceptibility of highly unsaturated fatty acids (HUFA) to oxidation during heating. 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