功能性n-3多不饱和脂肪酸的研究进展

脂肪酸是生命代谢活动中一种重要化合物，根据脂肪酸碳链数上的双键数将脂肪酸分为饱和脂肪酸、单不饱和脂肪酸、多不饱和脂肪酸三类。文章对n-3多不饱和脂肪酸来源、合成过程、n-3和n-6多不饱和脂肪酸的结构差异以及生物活性进行综述，为n-3多不饱和脂肪酸在功能保健食品、医学药用领域及基础研究进一步探索与全面开发提供理论依据。     

膳食中的脂肪酸平衡

本文综述了膳食中三类脂肪酸（饱和脂肪酸、单不饱和脂肪酸及多不饱和脂肪酸）的营养学功能，并就有关膳食脂肪酸的平衡及n-6与n-3的合适比例作了总结。     

鱼油软胶囊中脂肪酸组成及比率分析

采用气相色谱法对海洋鱼油软胶囊中脂肪酸组成和比率进行分析,为合理补充DHA、EPA等多不饱和脂肪酸提供理论依据,并为鉴别海洋鱼油质量提供基础数据。结果表明:鱼油软胶囊中主要含有C14~C22脂肪酸,其中不饱和脂肪酸质量分数50.8%~85.1%,特别是具有重要生理作用的多不饱和脂肪酸,如C20:5(EPA,约占10.0%~35.1%)、C22:6(DHA,约占10.7%~20.5%);鱼油软胶囊中n-3不饱和脂肪酸质量分数约为22.5%~55.7%,n-6不饱和脂肪酸与n-3不饱和脂肪酸的比率约为0~0.7,EPA与DHA的比率约为0.8~1.9。     

海水养殖花鲈和淡水养殖花鲈肌肉脂肪酸组成和含量分析

采用Folch 液回流提取投喂相同配合饲料的海水养殖花鲈和淡水养殖花鲈背部肌肉脂质,脂质经氢氧化钾-三氟化硼法甲酯化后进行气相色谱分析。结果表明：海水养殖花鲈和淡水养殖花鲈肌肉脂肪酸组成存在一定差异。海水花鲈肌肉脂肪酸中单不饱和脂肪酸(MUFA)、n-3 系列多不饱和脂肪酸(PUFA)、EPA(C20:5 n-3)和DHA(C22:6 n-3)含量明显高于淡水花鲈,而饱和脂肪酸(SFA)、n-6 系列PUFA 和AA(C20:4 n-6)含量则低于淡水养殖花鲈。海水养殖花鲈和淡水养殖花鲈肌肉中n-6 和n-3 系列PUFA 比值分别为0.27 和0.42,均远低于HMSO(英国卫生部)推荐的最高安全限值(4.0)。     

膳食中n-3多不饱和脂肪酸对2型糖尿病患者血糖和胰岛素敏感性的影响

2型糖尿病是世界上最常见的慢性疾病之一。膳食中的n-3多不饱和脂肪酸可能会减少亚洲人的2型糖尿病风险, 中国2型糖尿病患者血浆磷脂n-3不饱和脂肪酸与胰岛素敏感性呈正相关。而欧美的前瞻性研究均发现, 鱼类的摄入和n-3多不饱和脂肪酸的摄入会增加2型糖尿病的发病风险, 在西方白种人群中进行的n-3多不饱和脂肪酸干预的随机对照试验也并未发现n-3多不饱和脂肪酸能够改善患者胰岛素抵抗水平或血糖水平, n-3多不饱和脂肪酸甚至可轻微地降低患者胰岛素的敏感性。本文综述了目前n-3多不饱和脂肪酸摄入量与2型糖尿病风险之间的关系。     

黄颡鱼和大鳍(鳢)肌肉及鱼卵中脂肪酸组成的比较

采用GC测定了黄颡鱼和大鳍(镬)的脂肪酸组成.结果表明:在两种鱼的肌肉和鱼卵中含有22种脂肪酸.在黄颡鱼肌肉中饱和脂肪酸占34.90%;不饱和脂肪酸中,单不饱和脂肪酸占51.37%,多不饱和脂肪酸占13.74%.在黄颡鱼卵中,饱和脂肪酸占26.76%,单不饱和脂肪酸占49.51%,多不饱和脂肪酸占23.73%.从大鳍(镬)来看,肌肉中饱和脂肪酸占26.97%,单不饱和脂肪酸占48.8l%,多不饱和脂肪酸占24.23%;鱼卵中饱和脂肪酸占30.75%,单不饱和脂肪酸占44.08%,多不饱和脂肪酸占25.17%.研究揭示了黄颡鱼和大鳍(镬)的肌肉脂质中以不饱和脂肪酸为主,是理想的食品.两种鱼的鱼卵还含有较高的花生四烯酸(C20:4n-6,ARA)、廿碳五烯酸(C20:5n-3,EPA)和廿二碳六烯酸(C22:6n-3,DHA)的比例,鱼卵的食用、加工值得进一步研究和开发.     

小品种食用油的脂肪酸营养功能

分析论述了ω-3系列多不饱和脂肪酸(ω-3PUFA)、ω-6系列多不饱和脂肪酸(ω-6 PUFA)、单不饱和脂肪酸(MUPA)的特殊营养功效,阐述了不同类型的小品种食用油的脂肪酸营养特征。     

胎儿、婴幼儿的功能性多不饱和脂肪酸需要概况

探讨了胎儿、婴幼儿体内n-3、n-6系列多不饱和脂肪酸的水平与其正常发育的关联,在此基础上,介绍了包括DHA、花生四烯酸、γ－亚麻酸在内的强化多不饱和脂肪酸的婴幼儿乳粉配方及其营养模式。     

青海高原牦牛肉宰后成熟过程中脂肪酸组成及含量变化分析

为研究青海高原牦牛肉宰后成熟过程中不同部位肉脂肪酸组成和含量变化及差异,本实验选取青海高原牦牛冈上肌、背最长肌和半腱肌3个部位肉,利用气相色谱-质谱法(GC-MS)检测3个部位肉宰后成熟0、1、2、3、5、7和14 d的脂肪酸组成及含量。结果发现,3个部位肉中均检测出22种脂肪酸,其中,饱和脂肪酸8种,单不饱和脂肪酸5种,多不饱和脂肪酸9种,且均随宰后成熟时间的延长呈先增加后降低的趋势。3个部位肉宰后成熟过程中的脂肪酸组成相同但含量有差异,n-6/n-3比值均在1.0~3.0之间,脂肪酸组成比例较好。通过对青海高原牦牛3个不同部位肉不同成熟时间的脂肪酸组成及含量进行主成分分析,发现3个部位0、1和2 d具有相似性,主要有n-6系和n-3系多不饱和脂肪酸亚油酸(C18:2n6c)、花生四烯酸(C20:4n6)、顺-8,11,14-二十烷三烯酸(C20:3n6)、二十二碳六烯酸(C22:6n3)和单不饱和脂肪酸反油酸;3、5和7 d具有相似性,此期间大多数饱和脂肪酸、单不饱和脂肪酸和多不饱和脂肪酸含量增加;14 d则不同于其他时间,主要是此期间产生了大量的γ-亚麻酸(C18:3n6)。     

GC/MS分析俄罗斯鲟鱼不同部位脂肪酸组成

通过Folch法提取俄罗斯鲟鱼不同部位总脂,采用GC/MS法对其脂肪酸组成进行分析。通过质谱数据库检索和标准品对照鉴定脂肪酸组成。研究表明,鱼肉、鱼卵、鱼皮、鱼腹中脂肪酸种类及含量类似,多不饱和脂肪酸含量均大于40%,其次为单不饱和脂肪酸(30%左右)和饱和脂肪酸(17%左右),多不饱和脂肪酸以9,12-十八碳二烯酸和DHA为主。鱼肉中总脂含量12.83%,其中,多不饱和脂肪酸为42.37%,EPA+DHA为17.25%;鱼卵总脂含量为14.46%,其中n-3脂肪酸为22.10%;鱼皮含有较高含量的n-6脂肪酸(19.43%);鱼腹总脂含量14.45%,含有较高含量的多不饱和脂肪酸(42.66%)和单不饱和脂肪酸(34.07%),EPA+DHA为17.38%;鱼鳔中未检测到n-3和n-6脂肪酸;鱼肝总脂含量为55.92%,单不饱和脂肪酸含量尤为突出,高达55.81%,以9-十八碳烯酸(49.82%)为主,饱和脂肪酸含量仅为17.24%;椎骨中总脂仅为0.09%。     

Endogenous production and elevated levels of long-chain n-3 fatty acids in the milk of transgenic mice

n-3 Polyunsaturated fatty acids (n-3 PUFA) are important for the normal development and functioning of all organisms. Mammals lack the n-3 fatty acid desaturase required for the synthesis of α-linolenic acid (18:3n-3), and are therefore dependent on dietary sources to obtain this essential fatty acid. Currently, the richest source of dietary long-chain n-3 PUFA, eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3), are triacylglycerides extracted from rapidly declining marine resources. The nematode Caenorhabditis elegans synthesizes a wide range of PUFA and possesses the only known example of an n-3 fatty acid desaturase enzyme in the animal kingdom. Transgenic mice expressing the C. elegans n-3 desaturase under the control of the lactation-induced goat β-casein mammary gland promoter were generated via pronuclear microinjection. Significant increases in n-3 PUFA, decreases in n-6 PUFA, and an overall decrease in the n-6:n-3 PUFA ratio were observed in the milk produced by transgenic mice. Neonate mice consuming milk from transgenic females accumulated increased levels of docosahexaenoic acid in their brains. This transgenic model may provide useful information to address some basic questions of neonatal nutrition, and demonstrates one of the steps that would be required to increase the n-3 PUFA content of milk and dairy products endogenously. Increasing the proportion of n-3 PUFA in milk fat would help to improve the nutritional composition of an important component of the North American diet.     

Endogenous production of n-3 and n-6 fatty acids in mammalian cells

Polyunsaturated fatty acids (PUFA) are important components of mammalian diets, and the beneficial effects of n-3 PUFA on human development and cardiovascular health have been well documented. Caenorhabditis elegans is one of the few animals known to be able to produce linoleic (LA, 18:2n-6) and alpha-linolenic (ALA, 18:3n-3) essential fatty acids. These essential PUFA are generated by the action of desaturases that successively direct the conversion of monounsaturated fatty acids (MUFA) to PUFA. The cDNA coding sequences of the C. elegans Delta(12) and n-3 fatty acid desaturases were each placed under the control of separate constitutive eukaryotic promoters and simultaneously introduced into HC11 mouse mammary epithelial cells by adenoviral transduction. Phospholipids from transduced cells showed a significant decrease in the ratios of both MUFA:PUFA and n-6:n-3 fatty acids relative to control cultures. The fatty acid profile of transduced cellular phospholipids revealed significant decreases in MUFA and arachidonic acid (20:4n-6), and increases in LA, ALA, and eicosapentaenoic acid (20:5n-3). The fatty acid composition of triacylglycerols derived from transduced cells was similarly, but less dramatically, affected. These results demonstrate the functionality of C. elegans fatty acid desaturase enzymes in mammalian cells. Expression of these desaturases in livestock might act to counterbalance the saturating effect that rumen microbial biohydrogenation has on the fatty acid profile of ruminant products, and allow for the development of novel, land-based dietary sources of n-3 PUFA.     

海水鱼与淡水鱼omega-3多不饱和脂肪酸含量的比较研究

研究杭州市场常见野生和饲养淡水鱼以及海水鱼omega-3多不饱和脂肪酸（PUFA）的成分及含量。将购买的四个品种淡水鱼（野生和饲养）和六种海水鱼鱼肉去骨切碎,用有机溶剂提取总脂肪,甲酯化后的脂肪酸用气相色谱分离分析。结果表明：总PUFA的含量为从海水刺鲳的37．2mg／100g到淡水野生桂鱼的1821．8mg／100g,其中omeg-3PUFA有C18：3n-3,C18：4n-3,C20：5n-3,C22：5n-3,C22：6n-3,总omega-3PUFA含量为从海水刺鲳的32．3mg／100g到淡水饲养黑鱼的1104．3mg／100g。不同品种鱼脂肪酸含量存在显著性差异（p〈0．001）。结论：野生和饲养淡水鱼以及海水鱼中omega-3PUFA的含量及成分均因品种不同而异,淡水鱼的摄入完全能满足人体日常所需的omega3多不饱和脂肪酸。     

Effects of breed and a concentrate or grass silage diet on beef quality in cattle of 3 ages. I: Animal performance, carcass quality and muscle fatty acid composition

An increase in the intake of the n-3 series polyunsaturated fatty acids (PUFA) is recommended by nutritionists for the human diet and beef is a significant source of these fatty acids. Enhancing the n-3 PUFA content of beef is important in view of the generally saturated nature of fatty acids in ruminant meats and the potentially negative effect this can have on human health. This study examined the effects of breed and diet on the fatty acid composition of beef M. longissimus. Ninety-six steers were used, 48 Aberdeen Angus cross (AA) and 48 Holstein-Friesian (HF). At 6months of age, 3 groups were identified, to be slaughtered at 14, 19 and 24months, respectively. Each group consisted of eight steers of each breed fed on a concentrate or a grass silage diet, rich in n-6 and n-3 PUFA, respectively. The intake of the concentrate diet was restricted so that steers of each breed grew at a similar rate on each diet. The early maturing AA produced heavier, fatter carcasses with better conformation. Animals fed grass silage had higher carcass fatness and conformation scores and higher levels of neutral lipid and total lipid in muscle than those fed concentrate. When all animals were pooled, a decline in PUFA% as total muscle lipid increased was evident. Feeding a grass silage diet rich in α-linolenic acid (18:3n-3) increased levels of this fatty acid in muscle neutral lipid by a factor of about 3.0 compared with the concentrate diet, as well as enhancing the synthesis of the n-3 series long-chain C20-22 PUFA in the phospholipid fraction, including docosahexaenoic acid (DHA, 22:6n-3). In contrast, both levels and proportions of linoleic acid (18:2n-6) and the n-6 series C20-22 PUFA were higher in animals fed the concentrate diet. The proportions of 18:1trans and conjugated linoleic acid (CLA) in muscle neutral lipid were higher in animals fed concentrate compared with silage in all 3 groups. This was partly due to increased consumption of 18:2n-6. The ratio of PUFA to saturated fatty acids (P:S) in muscle was reduced by feeding grass silage, partly as the result of increased fat deposition. However, the increase in levels of n-3 series fatty acids with silage-feeding resulted in beneficially low n-6:n-3 ratios in muscle in all age groups (approximately 1.2 compared with 12.0 in the concentrate diet). Subtle breed differences in PUFA amounts and proportions were noted. Holstein-Friesians had higher proportions of PUFA and higher P:S ratios compared with AA, partly due to a higher proportion of phospholipid in total lipid. In phospholipid itself, HF in the 19 and 24months groups had higher proportions of most n-3 PUFA. In all age groups the ratio of DHA to its precursor, 18:3n-3 was higher in HF.     

Fatty acid content and composition of UK beef and lamb muscle in relation to production system and implications for human nutrition

Although ruminant meats normally have a low ratio of polyunsaturated fatty acids (PUFA) to saturated fatty acids (P:S ratio), the muscle contains a range of C(20) and C(22) PUFA of both the n-6 and n-3 series of potential significance in human nutrition. However, information on the amounts of these fatty acids in muscle and how they are modified by production system is limited In this study, the content and composition of fatty acids was determined in several muscles from beef steers fed grass (grazed) and bulls fed cereal concentrates. These are the two main types of beef production in the UK and Europe. Muscle fatty acids were also determined in lambs fed grass (grazed on pasture). The total fatty acid content of all muscles studied was less than 35 g kg(-1). The percentages in total fatty acids of all n-3 PUFA were higher in muscles from steers fed grass than from bulls fed concentrates whereas all n-6 PUFA were higher in the latter. The gluteobiceps muscle contained the largest amounts of fatty acids including PUFA and the m. longissimus dorsi the least amounts of PUFA in beef and lamb, and m. longissimus contained the lowest percentages of PUFA. Arachidonic acid was the major fatty acid in the C(20) + C(22) PUFA in beef from both production systems with twice as much in muscles from bulls fed concentrates. The P:S ratios were higher in the latter animals, range 0.21-0.34 compared with 0.08-0.13 in the steers fed grass. However, the n6:n-3 ratio was much less desirable in the bulls, 15.6-20.1 compared with 2.0-2.3 in the steers fed grass. These effects of production system in ruminants are larger than previously reported. Lamb muscle P:S ratios resembled those in grass-fed beef but the n-6:n-3 ratios were lower. The percentage of trans unsaturated 18:1 fatty acids was similar in both cattle production systems but lamb muscles contained twice as much as beef. Although the concentrations of the C(20) and C(22) PUFA are much lower than in fish, maintaining high n-3 levels in ruminant meats through grass feeding may be advantageous in human nutrition since meat is more widely consumed.     

Correlation of animal diet and fatty acid content in young goat meat by gas chromatography and chemometrics

The meat fatty acids (FA) profiles of caprines submitted to different dietary treatments were determined by gas chromatography. The data were treated by Chemometrics to consider all variables together. The contents of saturated FA (SFA), monounsaturated FA (MUFA), polyunsaturated FA (PUFA), omega-3 (n-3) FA, and omega-6 (n-6) FA in 32 samples were analyzed. PUFA:SFA and n-6:n-3 ratios were also considered. The multivariate methods of hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to analyze the experimental results. HCA can group samples according to their basic composition, and PCA can explain the relationship among the dietary treatments according to the meat fatty acid composition. Treatment 1 presented the highest n-6 FA concentration, PUFA:SFA, and n-6:n-3 ratios, and the lowest MUFA and n-3 concentrations. Opposite results were observed for treatment 4. Treatments 2 and 3 were highly similar with differences mainly in SFA and MUFA concentrations.     

The polyunsaturated fatty acid composition of beef and lamb liver

The effect on liver fatty acids of two typical beef production systems, steers fed grass (grazing) and bulls fed concentrates, was investigated. Liver fatty acids were also studied in lambs grazing grass. Total fatty acid content of liver in the beef animals was not affected by production system, being 3.5% for grass and 3.7% for concentrates although carcasses of the latter animals were leaner. The percentages of the major non polyunsaturated fatty acids (PUFA) were also similar: (concentrates in parentheses) 18:0, 25.2% (25.1%); 16:0, 13.3% (14.5%); 18:1 12.6% (14.0%). Total liver PUFA contents were similar for the two production systems and much higher than in muscle from the same animals. All n-3 PUFA were present in greater amounts in liver from grass fed animals and n-6 PUFA were higher in concentrate fed animals: mg/100g liver, 18:3n-3 92 (32); 20:5 n-3, 151 (17); 22:5 n-3, 283 (108); 22:6 n-3, 83 (32); 18:2 n-6, 172 (444); 20:4 n-6, 194 (270). The P:S ratios were 0.20 (grass) and 0.32 (concentrates) and the n-6:n-3 ratios were 0.71 and 4.8, respectively. Livers from grass-fed lamb had a higher fat content, 4.9%, than the beef livers and a lower percentage of 18:0, (21%); but more 16:0, (16%) and 18:1 (21 %). Total PUFA content of lamb's liver resembled that of beef liver and the composition was similar to that of the steers fed grass. However the concentrations of 18:3 n-3 and 22:6 n-3 were higher in lamb and contributed to a lower n-6: n-3 ratio of 0.46 although the P:S ratio of 0.18 was similar to that in beef liver. Ruminant liver is potentially a good source of C20 and C22 PUFA in the human diet particularly from grass fed animals, with a highly desirable n-6:n-3 ratio and this may be more important nutritionally than the low P:S ratio since people can offset this elsewhere in the diet.     

Effect of a linseed diet on lipid oxidation, fatty acid composition of muscle, perirenal fat, and raw and cooked rabbit meat

Forty Californian×New Zealand rabbits (1kg initial body weight) were fed a control or a linseed isoenergetic diet containing 30g of extruded linseed/kg. Twenty rabbits for each dietary treatment were slaughtered at 11 weeks of age, at 35 days after the start of the experiment. Feeding the linseed diet increased (P<0.005) the content of 18:2n-3 in muscles, perirenal fat, and raw and cooked meat. The long chain n-3 polyunsaturated fatty acid (PUFA) contents were also increased (P<0.01) in the meat. The linseed diet produced a robust decrease in the n-6/n-3 ratio. Cooking did not alter n-3 PUFA more than saturated fatty acids (SFA) or monounsaturated fatty acids (MUFA). However, n-6 PUFA were altered by cooking. The oxidative stability of Longissimus dorsi was not affected by the linseed diet, even after 300min of forced-oxidation. Inclusion of linseed in rabbit diets is a valid method of improving the nutritional value of rabbit meat.     

Effect of diets enriched in n-6 or n-3 fatty acids on dry matter intake,energy balance,oxidative stress,and milk fat profile of transition cows

The objective of this study was to determine the effect of dietary supplementation of n-3 polyunsaturated fatty acids (PUFA) and n-6 PUFA on dry matter intake (DMI), energy balance, oxidative stress, and performance of transition cows. Forty-five multiparous Holstein dairy cows with similar parity, body weight (BW), body condition score (BCS), and milk yield were used in a completely randomized design during a 56-d experimental period including 28 d prepartum and 28 d postpartum. At 240 d of pregnancy, cows were randomly assigned to one of the 3 isoenergetic and isoprotein dietary treatments, including a control ration containing 1% hydrogenated fatty acid (CON), a ration with 8% extruded soybean (HN6, high n-6 PUFA source), and a ration with 3.5% extruded flaxseed (HN3; high n-3 PUFA source). The HN6 and HN3 diets had an n-6/n-3 ratio of 3.05:1 and 0.64:1 in prepartum cows and 8.16:1 and 1.59:1 in postpartum cows, respectively. During the prepartum period (3, 2, and 1 wk before calving), DMI, DMI per unit of BW, total net energy intake, and net energy balance were higher in the HN3 than in the CON and NH6 groups. During the postpartum period (2, 3, and 4 wk after calving), cows fed HN3 and HN6 diets both showed increasing DMI, DMI as a percentage of BW, and total net energy intake compared with those fed the CON diet. The BW of calves in the HN3 group was 12.91% higher than those in the CON group. Yield and nutrient composition of colostrum (first milking after calving) were not affected by HN6 or HN3 but milk yield from 1 to 4 wk of milking was significantly improved compared with CON. During the transition period, BW, BCS, and BCS changes were not affected. Cows fed the HN6 diet had a higher plasma NEFA concentration compared with the CON cows during the prepartum period. Feeding HN3 reduced the proportion of de novo fatty acids and increased the proportion of preformed long-chain fatty acids in regular milk. In addition, the n-3 PUFA-enriched diet reduced the n-6/n-3 PUFA ratio in milk. In conclusion, increasing the n-3 fatty acids concentration in the diet increased both DMI during the transition period and milk production after calving, and supplementing n-3 fatty acids was more effective in mitigating the net energy balance after calving.