Past and Present Insights on Alpha-linolenic Acid and the Omega-3 Fatty Acid Family

Alpha-linolenic acid (ALA) is the parent essential fatty acid of the omega-3 family. This family includes docosahexaenoic acid (DHA), which has been conserved in neural signaling systems in the cephalopods, fish, amphibian, reptiles, birds, mammals, primates, and humans. This extreme conservation, in spite of wide genomic changes of over 500 million years, testifies to the uniqueness of this molecule in the brain and affirms the importance of omega-3 fatty acids. While DHA and its close precursor, eicosapentaenoic acids (EPA), have received much attention by the research community, ALA, as the precursor of both, has been considered of little interest. There are many papers on ALA requirements in experimental animals. Unlike humans, rats and mice can readily convert ALA to EPA and DHA, so it is unclear whether the effect is solely due to the conversion products or to ALA itself. The intrinsic role of ALA has yet to be defined. This paper will discuss both recent and historical findings related to this distinctive group of fatty acids, and will highlight the physiological significance of the omega-3 family.     

Enhancement of Omega-3 Fatty Acid Content in Rainbow Trout (Oncorhynchus mykiss) Fillets

ABSTRACT:  A commercial diet for rainbow trout ( Oncorhynchus mykiss ) was supplemented with 0 (control), 8.5%, or 15.0% (w/w) of flaxseed oil (FO). Trouts were harvested on days 0, 30, 60, 90, and 120. Boneless skinless trout fillets were recovered from fish and analyzed for fatty acid profile (FAP) and total fat. While the total fat levels of fillets were not ( P > 0.05) affected by FO supplementation, the FAP was. The lowest ( P < 0.05) proportion of saturated fatty acids was obtained from 15%, followed by 8.5% FO group, and the control group. The opposite results were observed for the unsaturated fatty acids. The highest ( P < 0.05) content of omega-3 fatty acids (ω-3 FA) in fillets was determined in the 15.0%, followed by the 8.5% FO group, and the control group. While the 15.0% and 8.5% of FO supplementation increased ( P < 0.05) concentration of linolenic acid (ALA, 18:3n3) in fillets, the eicosapentaenoic (EPA, 20:5n3) and docosahexaenoic acids (DHA, 22:6n3) contents decreased ( P < 0.05). At the same time, higher ( P < 0.05) concentration of linoleic (L, 18:2n6) and lower ( P < 0.05) concentration of arachidonic acids (AN, 20:4n6) in fillets were obtained in the 15.0% FO group compared with the control group. The ω-3/ω-6 FA ratio was also improved ( P < 0.05) by supplementing basal diet with 15.0% FO. Our results suggest that trout fillets with enhanced content of ω-3 FA can be developed from trout raised in aquaculture systems fed diets supplemented with 15.0% FO. These fillets could be a basis to develop novel functional aquatic foods for some niche markets.     

Omega-6支撑身体，Omega-3支撑大脑：均衡摄入对儿童大脑发育的影响（网络首发、推荐阅读）

人体大脑和身体的发育,需要从食物中摄取均衡的营养物质。人类大脑是区分人类和其他动物的特征。食物中的必需脂肪酸是机体组织结构和功能的必要组成部分。Omega-6（O6）亚油酸（LA6）是皮肤组织的组成成分,且是炎症、血栓形成、免疫和其他信号分子的前体;Omega-3（O3）α-亚麻酸（ALA3）,特别是其长链代谢产物——二十二碳六烯酸（DHA3）,是大脑、视网膜和部分神经组织中的关键组分。从富含LA6脂肪酸（缺乏O3脂肪酸）的植物籽中提取出的廉价而优质油脂,是20世纪的西方国家食品工业生产的主要脂肪来源。在代谢通路中,高浓度的LA6脂肪酸可拮抗O3脂肪酸代谢,造成O3脂肪酸不足,因此,在给怀孕动物的饲料中,只提供富含LA6但缺乏O3脂肪酸的油脂作为唯一的脂肪来源,会导致幼崽大脑发育不良。过去20~30年的研究表明,低含量LA6且含DHA3的油脂可改善大脑的功能。近年来的研究较多集中在营养因素对大脑发育的影响,最新研究数据表明,脂肪酸平衡对营养不良儿童的大脑发育尤为重要。世界卫生组织（WHO）越来越重视大脑的营养健康,通过其下属的食品法典委员会,建议用于治疗严重急性营养不良儿童的即食治疗食品中,使用含有均衡脂肪酸组成/构成的脂肪。同样,脂肪酸均衡对老年人可能也很重要。目前,业界已经有了调整油脂成分的方法,以确保脂肪酸均衡,从而维持人体整个生命周期的大脑健康。     

Omega-3 Fatty Acid Composition of Persian Gulf Fishes

The aim of this study was to investigate the content of omega-3 fatty acids in Persian Gulf fishes. The fishes were collected from Persian Gulf and the content of fatty acids in the head, muscle, and liver of fishes were determined. Quantitative analysis of fatty acids was performed by gas chromatography (GC) and methylmyristate was used as the reference material. GC and mass spectrometer (GC- mass) was applied for qualitative analysis and cod liver oil with all of omega-3 fatty acids was used as standard. Ghezel ala, Zamin kan-e-dom navari and Sorkhu mahi had maximum levels of omega-3 in total body. Halva Sefid, Gish-e-deraz baleh and Shamshiri were poor sources of omega-3. The liver of fish had the most content of omega-3 fatty acids followed by muscle and head, respectively.     

膳食脂肪酸构成及适宜推荐比值的研究概况

天然食物中的脂肪酸分为SFA、MUFA和PUFA,PUFA又包含n 6PUFA和n 3PUFA两类,由于它们具有不同的化学结构和物理性状,对健康亦产生不同的影响。大量研究显示,膳食中摄入SFA越高,血清TC越高,CHD发病率越高;膳食脂肪供能34%,MUFA供能18%～21%,可降低血清TC、LDL C、TG,并保持HDL C不降低,橄榄油、茶籽油富含MUFA,但必需脂肪酸不理想;PUFA具有降低血清LDL C水平的作用,玉米胚芽油、葵花籽油富含n 6PUFA,但缺乏n 3系α 亚麻酸以及不适宜的n 6 n 3的比值值得关注;膳食脂肪供能30%以下,SFA、MUFA和PUFA分别供能10%(即1∶1∶1)或<10%∶10%∶10%(<1∶1∶1)仍是目前最佳推荐值;不饱和脂肪酸中n 6 n 3的适宜推荐值是(4～6)∶1。     

ω-3多不饱和脂肪酸在改善鸡蛋营养质量方面的研究

本文对ω-3多不饱和脂肪酸的化学结构、特性、作用及在改善鸡蛋营养质量等方面的研究进行了综述,讨论了如何通过饲喂对鸡蛋的脂肪组分加以调控,从而使其成为人类ω-3多不饱和脂肪酸的重要来源。     

Omega-3脂肪酸磷脂制备方法综述

Omega-3脂肪酸磷脂生理功能明确,生物利用度高,在医药、保健品领域具有巨大的市场潜力,其制备方法是全球磷脂研究开发的新动向。综述了目前Omega-3脂肪酸磷脂的制备方法,包括天然提取法、酶促转化法、化学合成法及微生物发酵法。天然提取法是最早获得Omega-3脂肪酸磷脂产品的方法,主要包括溶剂萃取法、膜分离法、柱层析法和盐沉淀法;酶促转化法主要包括酶促酯交换法和酶促酯化法,是目前Omega-3脂肪酸磷脂合成效率最高、最常用的方法;化学合成法及微生物发酵法处于初步研究阶段,为Omega-3脂肪酸磷脂的制备提供了新的思路。     

研发生产富含Omega-3脂肪酸食品是改善民众营养健康状况的重要饮食策略（网络首发、推荐阅读）

Omega-6和Omega-3脂肪酸都是对细胞结构和功能非常重要的必需营养素,但人体不能合成,必须从食物中获得。这两类脂肪酸在代谢和功能上不同,并拮抗调节许多生理和病理过程。因此,Omega-6和Omega-3脂肪酸之间的相对平衡对健康至关重要。然而,现今的饮食中Omega-6过多,而Omega-3过少,导致严重失衡,大多数人体内的Omega-6/Omega-3 脂肪酸比率很高（>10）。许多证据表明,这个失衡是导致现代慢性疾病发生和发展的关键因素。越来越多的实验室及临床研究结果表明,通过增加机体组织中的Omega-3脂肪酸和/或减少Omega-6脂肪酸来均衡Omega-6/Omega-3脂肪酸的比例,对许多危及生命的慢性疾病的防治和促进公众健康都非常有益。因此,开发和生产富含Omega-3脂肪酸的食品应作为每个国家的一项健康重点工程,以平衡必需脂肪酸的摄入,从而改善人们的营养和健康状况。     

Physical and Oxidative Stabilization of Omega-3 Fatty Acids in Surimi Gels

ABSTRACT: The objective of the study was to compare the dispersion and oxidative stability of omega-3 fatty acid oil in high- and low-quality surimi gels during 4-mo refrigerated and frozen storage. Low-quality surimi was prepared by subjecting Alaska pollock surimi to 7 freeze–thaw cycles. Surimi gels were prepared with 4% modified starch, 2% salt, and 0.5% or 1% algal DHA or concentrated fish EPA-DHA oil, and stored at −18 or 3 °C for 4 mo after being vacuumed packed and pasteurized. The effect of surimi gel properties on oil dispersion was examined using light microscopy equipped with image process software. The extent of lipid oxidation was monitored by thiobarbituric acid reactive substances (TBARS), peroxide value (PV), and fatty acid methly esters (DHA and EPA). Very fine and uniform oil dispersion was observed in the high-quality surimi gel with the average droplet size of 12.37 μm² and dispersion of 1.73 × 10⁻³ droplets/μm² compared to 84.32 μm² and 0.57 × 10⁻³ droplets/μm² in the low-quality gel. Throughout the 4 mo storage, TBARS and PV of high-quality surimi gel were significantly (P < 0.05) lower than those of low-quality surimi gel. The decreases in omega-3 fatty acids in the high-quality surimi gels were lower than those in the low-quality surimi gels under both storage conditions. Results confirm that a highly cohesive gel matrix is required to have a fine dispersion and oxidative stability of omega-3 fatty acids in the surimi gel system. Practical Application: Uniform dispersion and oxidative stability of omega-3 fatty acid oil can be achieved in the highly cohesive surimi gel system without use of antioxidants. This suggests that surimi can be used as a protein-based carrier in developing high omega-3 fatty acids-containing seafood products.     

Fortification of Foods with Omega-3 Polyunsaturated Fatty Acids

A $600 million nutritional supplements market growing at 30% every year attests to consumer awareness of, and interests in, health benefits attributed to these supplements. For over 80 years the importance of polyunsaturated fatty acid (PUFA) consumption for human health has been established. The FDA recently approved the use of ω-3 PUFAs in supplements. Additionally, the market for ω-3 PUFA ingredients grew by 24.3% last year, which affirms their popularity and public awareness of their benefits. PUFAs are essential for normal human growth; however, only minor quantities of the beneficial ω-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are synthesized by human metabolism. Rather PUFAs are obtained via dietary or nutritional supplementation and modified into other beneficial metabolites. A vast literature base is available on the health benefits and biological roles of ω-3 PUFAs and their metabolism; however, information on their dietary sources and palatability of foods incorporated with ω-3 PUFAs is limited. DHA and EPA are added to many foods that are commercially available, such as infant and pet formulae, and they are also supplemented in animal feed to incorporate them in consumer dairy, meat, and poultry products. The chief sources of EPA and DHA are fish oils or purified preparations from microalgae, which when added to foods, impart a fishy flavor that is considered unacceptable. This fishy flavor is completely eliminated by extensively purifying preparations of n-3 PUFA sources. While n-3 PUFA lipid autoxidation is considered the main cause of fishy flavor, the individual oxidation products identified thus far, such as unsaturated carbonyls, do not appear to contribute to fishy flavor or odor. Alternatively, various compound classes such as free fatty acids and volatile sulfur compounds are known to impart fishy flavor to foods. Identification of the causative compounds to reduce and eventually eliminate fishy flavor is important for consumer acceptance of PUFA-fortified foods.

[Supplementary materials are available for this article. Go to the publisher's online edition of Critical Reviews in Food Science and Nutrition for the following free supplemental files: Additional text, tables, and figures.]     

Long Chain Omega-3 Fatty Acid Levels in Loin Muscle from Transgenic (fat-1 gene) Pigs and Effects on Lipid Oxidation During Storage

Studies suggest a diet rich in long chain omega-3 fatty acids (LCn3) can promote visual, neural and vascular health. Pork muscle typically has small amounts of LCn3. A transgenic technology involving the fat-1 gene has been developed to increase LCn3 in various pig tissues; however, pork loin muscle has not been examined to date. We have determined that the LCn3 content in loin muscle (Longissimus) from fat-1 pigs was 1.59–2.24 g/100 g lipid compared to 0.34–0.38 g/100 g lipid in control samples. Lipid oxidation products were measured in ground and salted loin muscle from control and fat-1 pigs during storage at ?4°C. There was no clear trend as to whether the fat-1 gene technology increased or decreased oxidative stability of the muscle during storage based on lipid peroxide and thiobarbituric acid reactive substances (TBARS) values. There were a greater number of volatiles detected in stored loin from fat-1 pigs compared to control. Volatiles common to control and fat-1 pigs were elevated in stored loin from fat-1 pigs. This is the first report indicating that the use of fat-1 transgenic technology significantly increases the amount of desirable LCn3 in pork loin muscle.     

多不饱和脂肪酸对小鼠3T3-L1前脂肪细胞增殖和分化的影响

本文利用MTS比色分析法、细胞形态学分析法及诱导分化法结合油红染色比色分析法研究了α-亚麻酸(alpha-linolenic acid,ALA)、亚油酸(linoleic acid,LA)对3T3-L1前脂肪细胞增殖及分化的影响。MTS结果显示,在一定浓度范围内ALA、LA均能呈剂量依赖关系和时间依赖关系的抑制3T3-L1前脂肪细胞的增殖,且ALA抑制增殖作用强于LA;细胞形态学分析结果显示,ALA、LA在高浓度时均显示出细胞毒性作用;倒置显微镜观察和油红染色检测结果显示,ALA、LA、ALA/LA混合脂肪酸(1:1,n/n)在12.5~200μmol/L浓度范围内均能浓度依赖式的抑制3T3-L1前脂肪细胞分化,且ALA抑制分化作用强于LA,但当浓度100μmol/L时,ALA/LA混合脂肪酸(1:1,n/n)的抑制分化作用强于同浓度的ALA,当浓度为200μmol/L时,比较ALA/LA摩尔比为1:4、1:2、1:1的混合脂肪酸抑制分化效果发现,比值为1:1的略强但相互之间效果差异不明显。     

反式脂肪酸的安全性评价

由于反式脂肪酸与心血管疾病等密切相关,所以在近几年来引起了大众和科学家的极大关注。本文主要对反式脂肪酸安全性的一些最新研究进展进行了综述。     

Fatty Acid Profile and Selected Chemical Contaminants in Yellowfin Tuna From the Arabian Sea

Fresh yellowfin tuna (n = 110) collected for a period of one year was analyzed for chemical composition, fatty acids, nutrients, and toxic metals. The mean values of investigated minerals were 892, 2834, 0.81, 6.61, 0.38, 11.0, 0.94, 0.59, 0.71, 0.53, and 0.29 mg kg^–1 for Na, K, Cu, Zn, Mn, Fe, Ni, Co, Cr, Sr, and V, respectively. Average Cd, Pb and Hg levels were 0.016, 0.029 and 0.137 mg kg^?1, respectively. The average concentrations of saturated, monounsaturated, and polyunsaturated fatty acids were 196.56, 84.8, and 218 mg 100g^–1, respectively. Yellowfin tuna contained higher DHA (148.2 mg 100g^–1) than EPA (29.3 mg 100 g^–1). A meal with 100 g of this species provides 48.6 and 71.05% of the required daily level of protein and EPA+DHA, respectively. Yellowfin tuna showed low thrombogenic (0.27) and atherogenic (0.43) potential and the value obtained for h/H index (1.97) indicates that regular intake of yellowfin tuna may bring hypocholesterolemic effect. All contaminants in the studied fish were either undetectable or present at very low levels when compared to the United States Food and Drug Administration (USFDA), Food and Agriculture Organization/World Health Organization (FAO/WHO), and European Union regulatory standards and yellowfin tuna would be one of the best options for people who frequently consume tuna fish to get sufficient EPA+DHA and essential elements.     

Hot topic: Enhancing omega-3 fatty acids in milk fat of dairy cows by using stearidonic acid-enriched soybean oil from genetically modified soybeans

Very long chain n-3 fatty acids such as eicosapentaenoic acid (EPA; 20:5n-3) are important in human cardiac health and the prevention of chronic diseases, but food sources are limited. Stearidonic acid (SDA; 18:4n-3) is an n-3 fatty acid that humans are able to convert to EPA. In utilizing SDA-enhanced soybean oil (SBO) derived from genetically modified soybeans, our objectives were to examine the potential to increase the n-3 fatty acid content of milk fat and to determine the efficiency of SDA uptake from the digestive tract and transfer to milk fat. Three multiparous, rumen-fistulated Holstein cows were assigned randomly in a 3 × 3 Latin square design to the following treatments: 1) control (no oil infusion); 2) abomasal infusion of SDA-enhanced SBO (SDA-abo); and 3) ruminal infusion of SDA-enhanced SBO (SDA-rum). The SDA-enhanced SBO contained 27.1% SDA, 10.4% α-linolenic acid, and 7.2% γ-linolenic acid. Oil infusions provided 57 g/d of SDA with equal amounts of oil infused into either the rumen or abomasum at 6-h intervals over a 7-d infusion period. Cow numbers were limited and no treatment differences were detected for DMI or milk production (22.9 ± 0.5 kg/d and 32.3 ± 0.9 kg/d, respectively; least squares means ± SE), milk protein percentage and yield (3.24 ± 0.04% and 1.03 ± 0.02 kg/d), or lactose percentage and yield (4.88 ± 0.05% and 1.55 ± 0.05 kg/d). Treatment also had no effect on milk fat yield (1.36 ± 0.03 kg/d), but milk fat percentage was lower for the SDA-rum treatment (4.04 ± 0.04% vs. 4.30 ± 0.04% for control and 4.41 ± 0.05% for SDA-abo). The SDA-abo treatment increased n-3 fatty acids to 3.9% of total milk fatty acids, a value more than 5-fold greater than that for the control. Expressed as a percentage of total milk fatty acids, values (least squares means ± SE) for the SDA-abo treatment were 1.55 ± 0.03% for α-linolenic acid (18:3n-3), 1.86 ± 0.02 for SDA, 0.23 ± <0.01 for eicosatetraenoic acid (20:4n-3), and 0.18 ± 0.01 for EPA. Transfer efficiency of SDA to milk fat represented 39.3% (range = 36.8 to 41.9%) of the abomasally infused SDA and 47.3% (range = 45.0 to 49.6%) when the n-3 fatty acids downstream from SDA were included. In contrast, transfer of ruminally infused SDA to milk fat averaged only 1.7% (range = 1.3 to 2.1%), indicating extensive rumen biohydrogenation. Overall, results demonstrate the potential to use SDA-enhanced SBO from genetically modified soybeans combined with proper ruminal protection to achieve impressive increases in the milk fat content of SDA and other n-3 fatty acids that are beneficial for human health.     

Oxidative Stability of Whey Protein-stabilized Oil-in-water Emulsions at pH 3: Potential ω-3 Fatty Acid Delivery Systems (Part B)

ABSTRACT: Consumption of omega-3 (ω-3) fatty acids is beneficial for human health. Incorporation of ω-3 fatty acids into functional foods is limited by their high susceptibility to oxidative degradation. Oil-in-water emulsions may be a more effective method to deliver ω-3 fatty acids into functional foods. Protein-stabilized oil-in-water emulsions at pH values below the isoelectric point of the protein produce cationic emulsion droplets that decrease the oxidation of lipids by decreasing iron-lipid interactions. This research showed that whey protein isolate (WPI)-stabilized algal oil emulsions at pH 3.0 had good physical and oxidative stability after pasteurization. Addition of ethylenediaminetetraacetic acid     

Proximate and fatty acids composition of the muscles and viscera of Asian catfish (Pangasius bocourti)

The objective of this research was to analyse the distribution pattern of proximate composition and fatty acid profiles in different portions of Asian catfish (Pangasius bocourti). The lipid content was found amongst different portions, ranging from 2.95% to 93.32%, being lowest in the caudal–dorsal portion and highest in the viscera. Protein, moisture and ash contents were inversely proportional to the lipid content amongst the body portion. There was no specific tendency for the changes of each fatty acid composition from the different portions. Monounsaturated fatty acid (MUFA) was the most predominant fatty acid found in all tissues, ranging from 32.7% to 39.9%, followed by saturated fatty acids (SFA) ranged from 30.2% to 36.5% of total fatty acid, whereas the total polyunsaturated fatty acids (PUFA) content was the lowest, ranging from 14.8% to 24.0%. This study revealed that the proximate compositions and fatty acids deposition in Asian catfish varied markedly throughout the body portion.