完成日期: 2013/11/9

DOI: 10.1002/fsn3.40食品科学与营养第 1 卷，第 4 期，网页 292–297， 2013 年 7 月

关键字：

∙ 脂肪酸组成；

∙ 煎炸；

∙ 油；

∙ 鲢鱼

摘要

四种不同的油炒的影响窗体顶端

(葵花籽油、大豆油、橄榄油、玉米油) 对鲢鱼脂肪酸的组成的影响进行了评估。油炸后在所有评价样品的水分含量降低的鱼片脂肪含量增加。意思是饱和脂肪酸(SFA)、单不饱和脂肪酸(MUFA)、多不饱和脂肪酸（PUFA）， ∑ω3和 ∑ω6含量的原料鱼分别是 26.1 ± 0.5、 52.1 ± 1.1，15.1 ± 0.6，8.9 ± 0.1 和 6.1 ± 0.4%。煎炸导致脂肪酸鲢鱼脂质和油炸用的脂肪之间的交换。作为一个相互作用的结果，MUFA，PUFA，∑ω6，和PUFA / SFA的比例样品炒向日葵，大豆和玉米油，显着增加，而大量的SFA下降。煎炸了 ∑ω3/ω6比消极影响但橄榄油煎样品中的减少是其他样品之间最小。除了在大豆油中长链 ω3-多不饱和脂肪酸含量的样品由油炸不受影响。

简介

海鲜是最丰富的 ω3来源-长-多不饱和脂肪酸 (LC-PUFA)，主要为二十碳五烯酸 (EPA， 20:5ω3) 和二十二碳六烯酸 (DHA，22:6ω3) 链。EPA和DHA的出现在个体发育中起着关键的作用，尤其是神经系统的发育、功能和心血管系统、免疫系统（Lauritzenet al. 2001年）的运作。ω3和ω6多不饱和脂肪酸（PUFA）被认为是必不可少的，但由于他们不能在人体内合成，它们必须通过饮食获得(Mahan 和Escott-Stump2005)。

水产养殖是实现发展中国家像伊朗人民的营养目标的手段之一。鲢鱼支持伊朗淡水渔业，是包括派遣内陆水产品总产量的 58%左右的最重要物种。鲢鱼 (鲢) 广泛应用于复合鱼文化，由于它的快速增长和抗应激、疾病和粗率的搬运。这一物种的消费对人类的营养尤其是在伊朗极为重要。

鱼通常是由伊朗人常见的食用油炸的形式。煎炸，特别深层脂肪油炸在过去的六年期间已成为最受欢迎的食物制备技术。原因是制备甚至对经验丰富更少的厨师是容易的，过程是快速的，和成品是非常美味(Gere 1982)。

复杂化学和物理所发生的变化过程中感官失败、营养价值下降和形成的化合物对健康产生不利影响的热操作结果。

脂肪酸组成的鲢鱼通常研究不考虑到烹饪加工，其中往往包括热处理和脂肪增加的影响。ZakipourRahimabadi和Dad (2012年) 确定煎炸对这一物种的薄切片的质量的影响。在上述研究中，没有调查的煎炸用油脂肪酸配置文件中的更改。本文的目的是研究如何在不同热油煎炸烹饪脂肪(向日葵油、橄榄油、玉米油、豆油)中脂肪酸组成影响脂肪和油炸鱼片,特殊的言论的内容关于EPA和DHA,LC-PUFAs和ω3 /ω6比率的变化。

材料和方法

示例程序

三十公斤的鲢鱼 (H.鲢; 48–51 厘米长和称重 1450–1660 g)是从本地存储在德黑兰，伊朗购买的，他们先前被运送在冷藏卡车的胡齐斯坦省、伊朗的农场后赶在冬天。捕捉和实验室到达之间的时间的流逝是小于30 h.头、鳞、内脏和尾巴被移除，并且从产生鱼取得了两个圆角。鱼片随后分为六均质组的每个2公斤。一组被保留原始用作参考、其他五个被炸焦。煎炸油脂是从本地存储在德黑兰，伊朗购买的。这种脂肪是由脂肪组成的选择条件：高单不饱和脂肪酸（MUFA）橄榄油，非常高的ω6 PUFA葵花籽油和玉米油，和大量的ω3 PUFA豆油（表3）。

煎炸

鲢鱼鱼片炸油炸锅（TEFAL，Visialis trade mark，法国）在 160 ° C 为 4 分钟。煎炸期间，内圆角温度监测与电子温度计（亲和素、科学标记、伊朗）。四种不同的植物油，如：葵花籽油、橄榄油、玉米油和大豆油等被用作煎炸的食物或油比率在 250 g/l。炒后，鱼片轻轻地排出大约 5 分钟。

分析

脂质样品的制备

每个地段的所有样本被都均质使用厨房搅拌机和分析，以确定水分、总脂和脂肪酸组成。组织匀浆样品进行了所有化验。原料和炒鱼片的水分含量确定的在 105 ° C 烘箱中干燥，直到一个恒定重量获得 (AOAC 1995年)。从脂肪中提取的原料和油炸鱼肉（Bligh 和Dyer (1959) 方法）。植物油 (葵花籽油、橄榄油、玉米油和大豆油) 之前和之后的油炸例经硫酸钠和分析以同样的方式为肉脂提取物。

脂肪酸组成

气相色谱法分析了脂肪酸甲酯 (FAME) 的葵花籽油、橄榄油、玉米油和大豆油和鱼类脂肪进行气相色谱分析。FAME是使用岛津分析（岛津17A，东京，日本）。气相色谱仪配有火焰电离探测器和熔融石英毛细管柱 (50–0.25 ° 毫米、 0.20 毫米的聚乙二醇20 mol/L)。柱温编程在2°C /分钟，从150到240°C.进样口和检测器分别保持在220和245°C。载气的氢气（1.2毫升/分钟），补充气体为氮气（30毫升/分钟），并使用1:100分裂。正常的脂肪酸的识别是通过比较FAME与标准样品Restek（海洋石油FAME混合目录35066号，Bellefonte，PA，USA）的相对保留时间、丰度和主要脂肪酸，这些通过另一个岛津17A（日本）气相色谱仪确认。

统计分析

SPSS ，版本 15.0 （斯坦福大学，加利福尼亚州，美国），用于统计分析。从不同的化学测量数据进行单因素方差分析（P＜0.05）。比较的手段是使用最小二乘法进行差分方法。

结果和讨论

水生生态系统已知的多不饱和脂肪酸的主要来源，人类通过食用鱼类（Arts et al. 2001年）获得 EPA 和 DHA 的主要部分。鱼的种类和烹调方式类型（热处理）可以在最终产品的必需脂肪酸含量的重要因素。鲢鱼是广泛养殖的品种。鲢鱼的水产养殖产量是世界最高的鱼产量，年全球生产近 420 万吨 (Naseri et al. 2010年)。水分和脂肪含量的样品后煎炸过程变化表1所示。鱼片的水分含量下降后油炸而脂肪含量在所有计算样本增加 (P ≤ 0.05)。

（Garcı′a-arias et al.2003年和 Cuesta et al.2001年），在煎炸，油击穿食物后水部分蒸发掉。脂肪含量和成分的原料鱼可以影响脂肪交换和烹饪脂肪和鱼的之间的相互作用（Muniz et al. 1992年）。煎炸富含PUFA的烹饪脂肪的含量显著增加，并可能通过两种机制，即在煎水损失和烹饪脂肪（Hakimeh et al. 2010年) 的吸收解释说。这些结果通过了Castrillón et al.(1997年)、Sanchez Muniz et al.(1992年)、ZakipourRahimabadi和Dad (2012年)的一致认定。根据表1的数据，橄榄油炒鱼片有比其他油炸样品脂肪少。Varela (1988年)指出橄榄油形成地壳,保护食品对吸收的油,而其他脂肪在煎炸后并不会形成这样一个定义的地壳和食品含有更多的脂肪。

表 1.总的可萃取脂肪和总水分的原料和煎鲢鱼

不同的字母 (a > b > c) 在同一行中表明油炸样本之间的一个重大区别 (P< 0.05)

鲢鱼和油炸的样品的脂肪酸组成如表2所示。在原料鲢鱼鱼片中找到，最丰富的脂肪酸是 (C18:1ω9) 油酸、棕榈酸 (C16:0) 及棕榈油酸 (C16:1ω7)。这些研究结果获得由Vujkovicet al.(1999年)的一致认定。鲢鱼鱼片还显示相当数量的硬脂酸 (C18:0)、亚油酸 (C18:2ω6) 和 DHA (C22:6ω3)。饱和的脂肪酸 (SFA) 内容几乎翻了一番，而ω3 PUFA的脂肪酸含量略高于ω6PUFA。EPA，DHA脂肪酸的量，和鲢在目前的研究中低于zakipourrahimabadi和Dad（2012）报告的平均值。但是，有可能取决于营养、性别、季节和环境条件的差异。

表 2.在原材料和煎鲢鱼的脂肪酸组成

值是表示作为三个单独确定 ± SD 的意思是总脂肪酸的百分比。字母间的差异 (a > b > c) 在行表明显著差异 (P ≤ 0.05)。SFA、MUFA；PUFA，单不饱和脂肪酸、多不饱和脂肪酸。

生鱼PUFA / SFA的比例是0.57，提高到0.8，1.27，1.68，和1.28后油炸橄榄油，葵花籽油，玉米有油，大豆油由于SFA减少和PUFA增加。这些变化是不相似的，这些结果由zakipourrahimabadi和Dad（2012）发现。当橄榄油为油炸介质，有可能依赖于油炸方法不同，倒角的尺寸和厚度，煎炸油的质量，和加热条件下。我们观察到的PUFA / SFA比值下降后油炸橄榄油（表3）。

表 3.煎炸油脂在煎炸过程前后脂肪酸组成 (占总脂肪酸 %)

值是表示作为三个单独确定 ± SD 的意思是总脂肪酸的百分比。字母间的差异 (a > b > c) 在行表明显著差异 (P ≤ 0.05)。在油炸前为BF；油炸后为AF；不饱和脂肪酸检测ND；SFA、MUFA；单不饱和脂肪酸，多不饱和脂肪酸，多不饱和脂肪；脂肪酸。

以往的调查显示热处理 (沸腾的水、油炸、烧烤、烧烤、烤箱烘烤，和微波烹调) 只有在ω3炸导致脂肪酸含量显著降低(García-Arias et al. 2003年;Gladyshevet al. 2006年)。在这次调查油炸显著改变脂肪酸组成的鲢鱼（表2）。经过油炸鲢鱼证实了鲢鱼脂肪酸的迁移在用于烹饪脂肪的绝对量的增加ω3PUFA。葵花籽油、大豆油、玉米油煎炸后EPA 含量增加 (表3)。Haak et al.(2007年)表明 LC-PUFA不显著由煎炸丢失，但它们的比例受到烹饪脂肪的吸收。在油炸过程中的一个特定的FA的增加或减少的幅度相对于FA梯度从烹饪脂肪鱼片。如表2和3所示，油炸涉及脂肪酸的烹饪脂肪和白鲢鱼之间的交换。这两种脂肪酸产品之间的相互作用引起的增加在白鲢鱼肌肉丰富把煎炸油中的脂肪酸的比例。长链多不饱和脂肪酸包括花生四烯酸 (AA，20： 4ω6）、EPA （20： 5ω3）和 DHA (22： 6ω3)。原料鲢鱼分别有 1.35 %aa，在橄榄油、葵花籽油、玉米油、大豆油煎炸后减至 0.92、 1.07、 0.86 和 0.58。原料鲢鱼包含 3.12 %EPA。炒后在大豆油中，脂肪酸含量的这被下降，虽然与其他示例显示无重大变化。油炸后，DHA 含量的鲢鱼并没有显著改变。这些研究结果与大马哈鱼是类似的Candella et al.(1998年) 和Sioen et al.(2006年) 。结果显示 DHA 含量的变化是比 EPA 和 AA 的为低。这些结果是与那些Echarte et al.(2001年)、Sioen et al.(2006年)，和ZakipourRahimabadi和Dad (2012年)。在比较不同的油脂的影响，发现煎炸豆油是保持LC-PUF量最坏的方式（AA，EPA，DHA）。表2显示的鲢鱼相对 Σω6内容增加时煎葵花籽油、玉米油和大豆油。另外多不饱和脂肪酸的量很重要，ω3/ω6的比率是已知的饮食的重要性。目前世卫组织的建议，ω3/ω6多不饱和脂肪酸不应低于 0.2 (Vujkovic et al. 1999年)。这项研究显示鲢鱼，像其他的海鲜，有很高 ω3/ω6的比例。煎的银鲤显著提高完成对亚油酸作为ω6-PUFA对ω3 /ω6比率产生不利影响。生鱼中的 ∑ω3/ω6含量是 1.44，然后在橄榄油、葵花籽油、玉米油和大豆油中油炸后分别减少到 1.14、 0.57、 0.32和 0.69。橄榄油∑ω3/ω6的减少相对其他油是最少的。虽然油炸工艺减少这个比例的值是比建议标准还高。

炒后，AA存在于葵花籽油、玉米油和大豆油中，EPA 和最后大豆油中的 DHA 被检测到。在鱼脂煎炸后由于渗透的 DHA 和 EPA （作为 ω3 LC-PUFA)，所有油∑ω3/ω6比例几乎增加了。

有些作者报告中在鱼品加工期间多不饱和脂肪酸水平下降（Tarley et al. 2004年），但也可能是物种特异性。使用类似的方法炸制Candella et al.(1998年) 和Sánchez-Munizetal.(1992年) 发现沙丁油鱼和鲭鱼的EPA和DHA减少三倍，而观察到的EPA和DHA含量无显著变化(Gladyshevet al. 2006年)。Sebedio et al.(1993年) 确认了在鱼的长链深层脂肪油炸和几何脂肪酸异构体的链长高度多不饱和脂肪酸形成过程中ω3多不饱和脂肪酸含量不受影响。由ZakipourRahimabadi和Dad (2012年) 发布的数据显示油炸（浅或深部脂肪油炸）方法可能导致中 DHA 和 EPA 的数额发生变化。油炸的富含PUFA的烹饪脂肪的鱼片增加PUFA的比例却对ω3 / ω6比产生不利影响。

结论

煎炸导致脂肪酸脂肪的白鲢鱼和用的烹饪脂肪之间的交换。煎炸用油的脂肪成分影响鲢鱼的脂肪酸组成。结果表明橄榄油炒鱼片比其他油炸样品产生脂肪少。由于鱼的脂肪酸的迁移，∑ω3 /ω6在所有的煎炸油比值升高（除橄榄油）。生鱼中的 ∑ω3/ω6内容被发现在所有减少评估样本。Ω3/ω6比例最高被发现时鲢鱼被橄榄油炒。豆油用作煎炸油时检测到的 EPA 和 DHA 含量最大减少。大豆油煎炸后发现有 ∑ω3/ω6含量最高。加工玉米油中发现了 ∑ω3/ω6的比例发生了重大变化。

附：

Effect of frying in different culinary fats on the fatty acid composition of silver carp

Article first published online: 30 MAY 2013

DOI: 10.1002/fsn3.40

© 2013 The Authors.Food Science & Nutrition published by Wiley Periodicals, Inc.

Food Science & Nutrition

Volume 1, Issue 4, pages 292–297, July 2013

Keywords:

∙ Fatty acid composition;

∙ frying;

∙ oil;

∙ silver carp

Abstract

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.

Introduction

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 (Hypophthalmichthysmolitrix) 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. ZakipourRahimabadi 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.

Materials and Methods

Sample procedures

Thirty kilograms of silver carp (H. molitrix; 48–51 cm long and weighing 1450–1660 g) was purchased from a local store in Tehran, Iran to where they had previously been transported in refrigerated trucks from the farms of Khuzestan, Iran after catch during the winter. The lapse of time between catching and arrival at the laboratory was <30 h. Head, scale, viscera, and tail were removed, and two fillets were obtained from the resulting fish. Fillets were subsequently divided into six homogeneous groups of 2 kg each. One group was kept raw and used as the reference and the other five were fried. Frying fats were purchased from a local store in Tehran, Iran. The choice of such fats was conditioned by their fat composition: high in monounsaturated fatty acids (MUFA) in olive oil, very high in ω6 PUFA in sunflower oil and corn oil, and considerable amount of ω3 PUFA in soybean oil (Table 3).

Frying

Silver carp fillets were fried in a deep fryer (TEFAL, Visialis trade mark, France) at 160°C for 4 min. During frying, the inner fillet temperature was monitored with an electronic thermometer (Aidin scientific trade mark, Iran). Four different vegetable oils, such as sunflower oil, olive oil, corn oil, and soybean oil, were used for frying with the food/oil ratios being 250 g/L. After frying, the fillets were gently drained for about 5 min.

Analysis

Preparation of the lipid samples

All samples in each lot were homogenized using a kitchen blender and analyzed to determine moisture, total lipid, and fatty acid composition. All assays were conducted on triplicate samples of the homogenates. The moisture content of raw and fried fillets was determined by drying in an oven at 105°C until a constant weight was obtained (AOAC 1995). Lipids were extracted from the raw and fried fish flesh following the Bligh and Dyer (1959) method. Vegetable oils (sunflower oil, olive oil, corn oil, and soybean oil) before and after frying were drained with sodium sulfate and analyzed in the same way as the flesh lipid extracts.

Fatty acid composition

The fatty acid methyl esters (FAME) of sunflower oil, olive oil, corn oil, and soybean oil and the fish fats were analyzed by gas chromatography. FAME were prepared by methylation of the triacylglycerols, as described by Naseri et al. (2010). The FAME were analyzed using a Shimadzu 17A (Shimadzu, Kyoto, Japan) gas chromatograph equipped with a flame ionization detector and a fused silica capillary column (50–0.25°mm and 0.20 mm of Carbowax 20 mol/L). The column temperature was programmed at 2°C/min from 150 to 240°C. The injection port and detector were maintained at 220 and 245°C, respectively. The carrier gas was hydrogen (1.2 mL/min), the make-up gas was nitrogen (30 mL/min), and the split used was 1:100. The identification of normal fatty acids was done by comparing the relative retention times of FAME peaks from samples with standards from Restek (Marine Oil FAME Mix-Catalog no. 35066, Bellefonte, PA, USA) and the main fatty acids, in order of abundance, were confirmed using another Shimadzu 17A (Japan) gas chromatograph.

Statistical analysis

SPSS, version 15.0 (Stanford, California, USA), was used for the statistical analysis. Data from the different chemical measurements were subjected to one-way analysis of variance (P < 0.05). Comparison of means was performed using a least-squares difference method.

Results and Discussion

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 ZakipourRahimabadi 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.

Different letters (a>b>c) in the same row indicate a significant difference between fried samples (P < 0.05).

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 ZakipourRahimabadi and Dad (2012). However, there are differences which may depend on nutrition, sex, season, and environmental conditions.

Values are percentage of total fatty acid expressed as mean ± SD of three separate determinations. Differences between letters (a>b>c) in rows indicate significant differences (P ≤ 0.05). SFA, saturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid.

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 ZakipourRahimabadi 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).

Values are percentage of total fatty acid expressed as mean ± SD of three separate determinations. Differences between letters (a>b>c) in rows indicate significant differences (P ≤ 0.05). BF, before frying; AF, after frying; ND, not detected; SFA, saturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid.

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 ZakipourRahimabadi 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 ZakipourRahimabadi 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.

Conclusion

Frying led to exchange of fatty acids between the fat in the silver carp and the culinary fats used. The fat compositions of frying oils affect the fatty acid composition of silver carp. Results showed that olive oil-fried fillets had less fat than the other fried samples. The ∑ω3/ω6 ratio increased in all frying oils (except in olive oil) due to migration of fish fatty acids. The ∑ω3/ω6 content in raw fish was found to be reduced in all evaluated samples. The highest ω3/ω6 ratio was found when silver carp was fried in olive oil. Maximum reduction in EPA and DHA content was detected when soybean oil was used as the frying oil. The highest ∑ω3/ω6 content was observed in soybean oil after frying. The Major changes in ∑ω3/ω6 ratio were found in corn oil after processing.

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