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- Materials and Methods
- Results and Discussion
- Conflict of Interest
The influence of frying with four different oils (sunflower oil, soybean oil, olive oil, and corn oil) on the fatty acid composition of silver carp was evaluated. The fat content of the fillets increased after frying while the moisture content decreased in all evaluated samples. Mean saturated (SFA), monounsaturated (MUFA), polyunsaturated (PUFA) fatty acids, ∑ω3, and ∑ω6 contents of raw fish were 26.1 ± 0.5, 52.1 ± 1.1, 15.1 ± 0.6, 8.9 ± 0.1, and 6.1 ± 0.4%, respectively. Frying led to exchange of fatty acids between the silver carp lipid and frying fats. As a result of interactions, MUFA, PUFA, ∑ω6, and PUFA/SFA ratio of samples fried in sunflower, soybean, and corn oil significantly increased while the amounts of SFA decreased. Frying had a negative effect on the ∑ω3/ω6 ratio but reduction in olive oil-fried samples is the least among the other samples. Except in soybean oil, long-chain ω3-PUFA content of samples was not affected by frying.
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- Materials and Methods
- Results and Discussion
- Conflict of Interest
Seafoods are rich sources of ω3-long-chain polyunsaturated fatty acids (LC-PUFA), mainly eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3). EPA and DHA appeared to play a key role in ontogenesis, especially neural development, functioning of cardiovascular system, and immune systems (Lauritzen et al. 2001). ω3 and ω6 polyunsaturated fatty acids (PUFA) are considered essential but since they cannot be synthesized in the human body, they must be obtained through diet (Mahan and Escott-Stump 2005).
Aquaculture is one of the means to achieve the nutritional goal of people in developing countries like Iran. Among the various fresh water fish supporting the Iranian fresh water fishery, carp are the most important species contributing about 58% of the total inland fish production. Silver carp (Hypophthalmichthys molitrix) is widely used in the composite fish culture, due to its quick growth and resistance to stress, disease, and rough handling. Consumption of this species is of crucial importance for human nutrition, especially in Iran.
The fish is commonly consumed in fried form by Iranian people. Frying, especially deep fat frying has become the most popular food preparation technology during the last six decades. The reason is that the preparation is easy even for less experienced cooks, the procedure is rapid, and the finished product is highly palatable (Gere 1982).
The complex chemical and physical changes that occur during the thermal operation result in organoleptic failures, a decrease in nutritive value, and the formation of compounds with adverse effects on health.
Studies on the fatty acid composition of silver carp usually do not take into account the influence of culinary processing, which often includes a heat treatment and fat addition. Zakipour Rahimabadi and Dad (2012) determined the influence of frying on the quality of thin slices of this species. In the mentioned research, the changes in fatty acid profiles of frying oils were not investigated. The purpose of this paper was to study how deep fat frying in different culinary fats (sunflower oil, olive oil, corn oil, and soybean oil) affected the fatty acid composition of fish fillet and frying fats, with special remarks concerning the content of EPA and DHA, LC-PUFAs and ω3/ω6 ratio changes.
Results and Discussion
- Top of page
- Materials and Methods
- Results and Discussion
- Conflict of Interest
Aquatic ecosystems are known to be the main source of PUFAs and humans gain major part of EPA and DHA by consuming fish (Arts et al. 2001). Type of fish species and way of cooking (kind of heat treatment) may be important factors for content of the essential fatty acids in final products. Silver carp is an extensively cultured species. Aquaculture production of silver carp is the highest of any fish species in the world that has an annual global production of nearly 4.2 million metric tons (Naseri et al. 2010). The changes in moisture and fat content of samples after frying processes are shown in Table 1. The moisture content of the fish fillets decreased after frying while the fat content increased in all evaluated samples (P ≤ 0.05). According to Garcı′a-Arias et al. (2003) and Cuesta et al. (2001), during frying, oil penetrates the food after water is partially lost by evaporation. The fat content and composition of raw fish can influence fat exchanges and interactions between the culinary fat and that of the fish when frying (Sánchez-Muniz et al. 1992). The increase of the fat content in the meat fried in the PUFA-enriched culinary fat was significant and may be explained by two mechanisms, namely the loss of water during frying and the absorption of culinary fat (Hakimeh et al. 2010). These results are in agreement with those of Castrillón et al. (1997), Sánchez-Muniz et al. (1992), and Zakipour Rahimabadi and Dad (2012). According to the data of Table 1, olive oil-fried fillets had less fat than the other fried samples. Varela (1988) indicated that olive oil forms a crust that protects the food against absorption of oils, whereas other fats do not form such a defined crust and the food contains more fat after frying.
Table 1. Total extractable lipid and total moisture content in raw and fried silver carp
|%||Raw fish||Olive oil-fried fillet||Sunflower oil-fried fillet||Corn oil-fried fillet||Soybean oil-fried fillet|
|Moisture||74.15 ± 0.91a||66.12 ± 1.31b||64.11 ± 1.42c||63.46 ± 0.89c||62.98 ± 1.19c|
|Lipid||10.97 ± 1.27c||11.85 ± 0.41b||13.15 ± 1.34a||12.98 ± 1.45a||13.03 ± 0.76a|
The fatty acid composition of silver carp and fried samples is shown in Table 2. The most abundant fatty acids found in raw silver carp fillets were oleic acid (C18:1ω9), palmitic acid (C16:0), and palmitoleic acid (C16:1ω7). These findings are in agreement with those obtained by Vujkovic et al. (1999). Silver carp fillets also showed considerable amounts of stearic acid (C18:0), linoleic acid (C18:2ω6), and DHA (C22:6ω3). The saturated fatty acid (SFA) content was almost double that of PUFA while the ω3 fatty acid content was higher than that of ω6 fatty acids. The amount of EPA, DHA, and PUFA in silver carp in the current study was lower than the mean values reported by Zakipour Rahimabadi and Dad (2012). However, there are differences which may depend on nutrition, sex, season, and environmental conditions.
Table 2. Fatty acid composition in raw and fried silver carp
|Fatty acids||Raw fish||Olive oil-fried fillet||Sunflower oil-fried fillet||Corn oil-fried fillet||Soybean oil-fried fillet|
|14:0||1.51 ± 0.1b||1.61 ± 0.07b||2.35 ± 0.07a||1.47 ± 0.14b||1.94 ± 0.65ab|
|14:1ω7||0.31 ± 0. 05b||0.39 ± 0.03b||0.57 ± 0.01a||0.37 ± 0.02b||0.40 ± 0.10ab|
|16:0||20.41 ± 0.35a||15.65 ± 0.55bc||16.02 ± 0.09b||14.76 ± 0.69d||14.96 ± 0.42cd|
|16:1ω7||9.80 ± 0.02b||8.07 ± 0.56b||10.59 ± 0.10a||8.91 ± 0.55ab||7.16 ± 0.60b|
|18:0||2.91 ± 0.42c||2.75 ± 1.11c||2.74 ± 0.11c||6.63 ± 0.31a||4.21 ± 0.34b|
|18:1ω9||38.27 ± 0.84a||44.84 ± 3.36a||26.03 ± 0.44b||22.50 ± 1.60bc||20.19 ± 0.74c|
|18:1ω7||1.43 ± 0.23bc||1.21 ± 0.05c||1.76 ± 0.11b||3.88 ± 1.01a||3.12 ± 0.13a|
|18:2ω6||2.86 ± 0.11d||5.79 ± 0.13c||15.5 ± 0.09b||26.98 ± 4.45a||15.09 ± 1.11b|
|18:3ω3||4.87 ± 0.15bc||4.25 ± 0.24c||5.11 ± 0.02b||4.34 ± 0.23bc||7.38 ± 0.83a|
|20:1ω11||0.66 ± 0.03a||0.14 ± 0.007bc||0.17 ± 0.05b||0.15 ± 0.01bc||0.12 ± 0.02c|
|20:0||1.75 ± 0.06b||1.75 ± 0.08b||2.09 ± 0.02a||1.89 ± 0.11ab||1.44 ± 0.24c|
|20:2ω6||1.47 ± 0.06a||1.06 ± 0.23b||1.14 ± 0.02b||1.59 ± 0.16a||0.74 ± 0.12c|
|20:3ω6||0.51 ± 0.14a||0.11 ± 0.005b||0.19 ± 0. 01b||0.14 ± 0.01b||0.10 ± 0.06b|
|20:4ω6||1.35 ± 0.18a||0.92 ± 0.06bc||1.07 ± 0.05b||0.86 ± 0.07bc||0.58 ± 0.34c|
|20:5ω3||3.12 ± 0.42a||2.73 ± 0.13ab||3.03 ± 0.22a||2.52 ± 0.25abc||2.21 ± 0.10c|
|22:0||0.63 ± 0.14ab||0.69 ± 0.07a||0.77 ± 0.04a||0.67 ± 0.06ab||0.50 ± 0.10b|
|22:1ω9||0.54 ± 0.02a||0.52 ± 0.04a||0.55 ± 0.02a||0.51 ± 0.07a||0.43 ± 0.07a|
|22:6ω3||2.25 ± 0.05a||2.00 ± 0.12a||2.13 ± 0.18a||2.16 ± 0.15a||1.90 ± 0.38a|
|SFA1||26.18 ± 0.50a||20.87 ± 0.92c||22.06 ± 0.07c||23.69 ± 1.16b||21.75 ± 0.91c|
|MUFA2||52.14 ± 1.18b||56.81 ± 2.83a||41.87 ± 0.17c||38.08 ± 3.01d||32.78 ± 1.66e|
|PUFA3||15.09 ± 0.62d||16.89 ± 0.74d||28.19 ± 0.58b||38.63 ± 4.51a||28.02 ± 1.88b|
|∑ω3||8.90 ± 0.16b||8.99 ± 0.50b||10.28 ± 1.61b||9.04 ± 0.48b||11.50 ± 1.13a|
|∑ω6||6.19 ± 0.47c||7.89 ± 0.24c||17.91 ± 0.03b||29.59 ± 4.58a||16.52 ± 0.77b|
|∑ω3/ω6||1.44 ± 0.08a||1.14 ± 0.02b||0.57 ± 0.03d||0.32 ± 0.05e||0.69 ± 0.03c|
|PUFA/SFA||0.57 ± 0.02d||0.80 ± 0.01c||1.27 ± 0.02b||1.68 ± 0.26a||1.28 ± 0.03b|
Frying in PUFA-enriched culinary fat caused a decline in the proportion of SFA, while the proportion of MUFA remained unchanged and the proportion of PUFA markedly increased in sardines (Sánchez-Muniz et al. 1992). Particularly, the proportions of linoleic acid (C18:2ω6) was increased because of the fatty acid (FA) composition of the fried meat that tended to become similar to that of the culinary fat (Sánchez-Muniz et al. 1992). Gall et al. (1983) found that frying with soybean oil produced a considerable decrease in the SFA content of all fish studied. Palmitic acid was the major SFA in the raw fish, but during the deep fat frying process it decreased, producing the most important reduction in sardines and mackerel. This was also found in this investigation and other researches (Gall et al. 1983; Sánchez-Muniz et al. 1992; Zakipour Rahimabadi and Dad 2012). Different effects of frying on saturated and MUFA could be explained by the kind of analyzed fish (initial fat content and fillet thickness) as well as cooking oil selected. These results are shown for silver carp under deep frying in Table 2. PUFA/SFA ratio in raw fish is 0.57 and this increased to 0.8, 1.27, 1.68, and 1.28 after frying in olive, sunflower, corn, and soybean oil due to SFA reduction and PUFA increase. These changes were not similar to those found by Zakipour Rahimabadi and Dad (2012) when olive oil was used as the medium of frying. There are differences which may depend on frying method, fillet size and thickness, quality of frying oil, and heating conditions. We observed a decline in the ratio of PUFA/SFA after frying in olive oil (Table 3).
Table 3. Fatty acid composition (% of total fatty acids) of frying fats before and after frying process
|Fatty acids||Olive oil||Sunflower oil||Corn oil||Soybean oil|
|16:0||11.99 ± 0.15b||12.76 ± 0.32a||6.42 ± 0.10a||6.46 ± 0.01a||11.34 ± 0.15a||11.37 ± 0.13a||11.18 ± 0.15a||11.08 ± 0.30a|
|16:1ω7||0.72 ± 0.008||ND||ND||0.10 ± 0.05||ND||ND||ND||0.10 ± 0.007|
|18:0||ND||ND||4.39 ± 0.50a||4.42 ± 0.11a||2.88 ± 0.10||ND||4.09 ± 0.28a||3.77 ± 0.23a|
|18:1ω9||75.71 ± 0.85a||73.64 ± 1.41a||24.20 ± 1.31a||24.88 ± 0.15a||25.43 ± 0.75a||27.71 ± 2.07a||23.09 ± 0.96a||24.91 ± 0.72a|
|18:2ω6||9.17 ± 0.10a||8.83 ± 0.41a||62.98 ± 0.80a||62.20 ± 0.37a||57.93 ± 0.44a||55.10 ± 0.60b||53.78 ± 0.36a||52.05 ± 0.82b|
|18:3ω3||0.52 ± 0.01||ND||0.21 ± 0.03a||0.15 ± 0.001a||0.37 ± 0.01a||1.74 ± 0.01a||6.89 ± 0.04a||6.94 ± 0.16a|
|20:1ω11||0.23 ± 0.05||ND||0.14 ± 0.02b||0.23 ± 0.005a||ND||ND||ND||0.38 ± 0.008|
|20:0||0.40 ± 0.01a||0.35 ± 0.02a||ND||ND||ND||0.20 ± 0.04||ND||0.17 ± 0.005|
|20:3ω6||ND||0.10 ± 0.01||ND||ND||ND||ND||ND||ND|
|20:4ω6||ND||ND||ND||0.63 ± 0.005||ND||ND||ND||ND|
|20:5ω3||ND||ND||ND||0.21 ± 0.001||ND||0.15 ± 0.006||ND||0.38 ± 0.008|
|22:6ω3||ND||ND||ND||ND||ND||ND||ND||0.12 ± 0.003|
|∑SFA||12.40 ± 0.14b||13.11 ± 0.30a||10.81 ± 0.59a||10.95 ± 0.10a||14.22 ± 0.05a||11.62 ± 0.16b||15.27 ± 0.43a||15.07 ± 0.31a|
|∑MUFA||76.67 ± 0.85a||73.64 ± 1.41b||24.35 ± 1.29a||25.22 ± 0.15a||25.43 ± 0.75a||27.71 ± 2.07a||23.09 ± 0.96b||25.41 ± 0.73a|
|∑PUFA||9.69 ± 0.10a||8.94 ± 0.40b||63.20 ± 0.80a||63.20 ± 0.38a||58.30 ± 0.46a||57.007 ± 0.6b||60.67 ± 0.39a||59.51 ± 0.69a|
|∑ω3||0.52 ± 0.10||ND||0.21 ± 0.03b||0.36 ± 0.003a||0.37 ± 0.01b||1.90 ± 0.01a||6.89 ± 0.04b||7.46 ± 0.17a|
|∑ω6||9.17 ± 0.10a||8.94 ± 0.40a||62.98 ± 0.80a||62.83 ± 0.37a||57.93 ± 0.44a||55.10 ± 0.60b||53.78 ± 0.36a||52.05 ± 0.85b|
|∑ω3/ω6||0.05 ± 0.001||ND||0.003 ± 0. 005b||0.005 ± 0.0a||0.0006 ± 0.00b||0.03 ± 0.006a||0.12 ± 0.005b||0.14 ± 0.005a|
|PUFA/SFA||0.78 ± 0.002a||0.68 ± 0.03b||5.85 ± 0.39a||5.76 ± 0.08a||4.09 ± 0.01b||4.90 ± 0.02a||3.97 ± 0.10a||3.94 ± 0.11a|
Previous investigations showed that of the different methods of heat treatment (boiling in water, frying, roasting, grilling, oven-baking, and microwave cooking), only frying resulted in a statistically significant decrease in ω3 fatty acid content (García-Arias et al. 2003; Gladyshev et al. 2006). In this investigation, frying significantly changed the fatty acid composition of silver carp (Table 2). The increase in the absolute amount of ω3-PUFA in the used culinary fats after frying of silver carp confirms the migration of fatty acids from the silver carp. The EPA content of sunflower, soybean, and corn oil after frying increased (Table 3). Haak et al. (2007) showed that LC-PUFAs were not significantly lost by frying, but their proportions were influenced by the uptake of culinary fat. The extent of the increase or decrease of a particular FA during frying was relative to the FA gradient from the culinary fat to the fish fillet. As indicated in Tables 2 and 3, frying involves an exchange of fatty acids between the culinary fat and that of the silver carp. The interaction between both fatty products caused an increase in the silver carp muscle of proportion of the fatty acids abundant in the frying oils. Long-chain PUFA include arachidonic acid (AA, 20: 4ω6), EPA (20: 5ω3), and DHA (22: 6ω3). Raw silver carp has 1.35% AA that after frying in olive, sunflower, corn, and soybean oil is reduced to 0.92, 1.07, 0.86, and 0.58, respectively. Raw silver carp contains 3.12% EPA. After frying in soybean oil, the content of this fatty acid was decreased, while the other samples showed no significant change. DHA content of silver carp did not change significantly after frying. These findings are similar to those of Candella et al. (1998) and Sioen et al.(2006) in salmon. The results show that variation in DHA content is lower than that of EPA and AA. These results are in agreement with those of Echarte et al. (2001), Sioen et al. (2006), and Zakipour Rahimabadi and Dad (2012). On comparing the effects of different fats, it was discovered that frying with soybean oil is the worst way to keep the amounts of LC-PUF (AA, EPA, and DHA). Table 2 shows that the relative Σω6 content of silver carp increased when fried in sunflower, corn, and soybean oil. In addition importance of the amount of PUFA, ratio of ω3/ω6 is known to be of dietetic importance. According to the current WHO recommendations, ω3/ω6 PUFA should not be lower than 0.2 (Vujkovic et al. 1999). This study showed that silver carp, like other seafood, have a high ω3/ω6 ratio. Frying of silver carp accomplished with significant increasing on linoleic acid as ω6-PUFA, which had negative effects on the ω3/ω6 ratio. The ∑ω3/ω6 content in raw fish was 1.44, which then reduced to 1.14, 0.57, 0.32, and 0.69 after frying in olive, sunflower, corn, and soybean oil, respectively. ∑ω3/ω6 reduction in olive oil is the least among the other oils. Although the frying process decreased this ratio, the values are still higher than the recommended standard.
After frying, AA in sunflower oil, EPA in sunflower, corn and soybean oil, and finally DHA in soybean oil were detected. The ∑ω3/ω6 ratio increased almost in all oils after frying due to the penetration of DHA and EPA (as ω3 LC-PUFA) from fish lipid.
Some authors reported a decrease in PUFA levels during fish processing (Tarley et al. 2004), but it may also be species specific. Using a similar method of frying, Candella et al. (1998) and Sánchez-Muniz et al. (1992) found a threefold decrease in EPA and DHA in sardines and mackerel, whereas no significant changes in EPA and DHA content were observed (Gladyshev et al. 2006). Sebedio et al. (1993) affirmed that the longer chain ω3 PUFA content of mackerel was not affected by deep fat frying and geometrical fatty acid isomers of long-chain highly PUFA were formed during this process. Data published by Zakipour Rahimabadi and Dad (2012) showed that the method of frying (shallow or deep fat frying) could cause changes in the amounts of DHA and EPA. Frying in the PUFA-enriched culinary fat increased the PUFA proportion in the fish fillet but had a negative effect on the ω3/ω6 ratio.