氢化大豆油和反刍动物油脂中甘油三酯和磷脂反式脂肪酸的位置分布

以氢化大豆油和反刍动物脂质为研究对象,采用Folch法提取油脂,氨丙基硅胶固相萃取小柱分离出油脂中的甘油三酯和磷脂,利用Sn-1,3专一性脂肪酶作用甘油三酯得到Sn-2甘油一酯和游离脂肪酸,磷脂酶A2作用磷脂得到游离脂肪酸和Sn-1溶血磷脂,并通过气相色谱分析2种不同来源油脂反式脂肪酸在甘油三酯和磷脂中的含量和位置分布情况。结果表明,反式脂肪酸占氢化大豆油甘油三酯总脂肪酸的41.466%,占反刍动物油脂甘油三酯总脂肪酸的2.451%~3.179%。反式脂肪酸在氢化大豆油甘油三酯中主要分布在Sn-2位,而在反刍动物油脂甘油三酯中主要分布在Sn-1,3位,在反刍动物油脂磷脂中则易分布在Sn-1上。不同来源的反式脂肪酸的膳食摄入量及其在甘油三酯中的位置分布不同,可能是导致不同来源反式脂肪酸对人体健康影响差异的原因。     

Ag+-SPE／GC测定食物中trans C16：1，trans C18：1，trans C18：2和共轭亚油酸的含量

为研究不同来源的反式脂肪酸(TFAs)对人体健康的影响,本文拟调查食物中trans C_(16:1),trans C_(18:1),trans C_(18:2)和共轭亚油酸(CLA)异构体的组成和含量,为明确不同食物中TFAs和CLA与健康的关系提供科学理论依据。结合银离子固相萃取柱(Ag~+-SPE)和GC色谱2种升温程序测定反刍动物油脂、食用油和煎炸油中trans C_(16:1),trans C_(18:1),trans C_(18:2)和CLA异构体的含量。结果显示,从样品中共检测出23种TFAs,其中7种trans C_(16:1),10种trans C_(18:1),6种trans C_(18:2)和6种CLA异构体。反刍动物油脂中trans C_(16:1), trans C_(18:1)和CLA显著高于食用油和煎炸油,而煎炸油中trans C_(18:2)含量较高。反刍动物油脂中9t C_(16:1),11t C_(18:1),9t12t C_(18:2)是主要TFAs异构体,10t12c C_(18:2)是主要的CLA异构体;而食用油和煎炸油中12t C_(16:1),9t C_(18:1),9c12t C_(18:2),9t12c C_(18:2)为主要的TFAs异构体,10t12c C_(18:2)和11c13t C_(18:2)是CLA的主要异构体。通过食用油煎炸前、后脂肪酸的对比发现,茶籽油脂肪酸组成变化最小,而大部分煎炸油比未煎炸油中trans C_(18:2),trans C_(18:1)的含量显著增加。可见,反刍动物油脂和食用油、煎炸油中主要TFAs异构体不同,而不同异构体脂肪酸对人体健康影响不同。茶籽油煎炸前后脂肪酸组成变化较小,食用中适合煎炸;而富含多不饱和脂肪酸的食用油经煎炸后会产生较多的对人体健康存在更大隐患的trans C_(18:2),因此对煎炸油品质的控制应引起有关生产和使用企业的高度重视。     

中国居民膳食中原料食物的各种反式脂肪酸的调研

通过本实验室建立的Ag+-TLC/GC连用技术测定我国日常膳食组成的原料食物中反式脂肪酸(TFAs)含量。测定结果表明我国食物中普遍存在反式脂肪酸,9t C18:1、10t-C18:1、11t C18:1和9t12t C18:2是其存在的主要形式。反刍动物产品中存在较高的9t C16:1、t C18:1和9t12t C18:2等各种反式脂肪酸(仅羊肉中未检出9t12t C18:2),且均以t C18:1为主,其中奶粉、奶油、鲜牛奶和酸奶等奶制品中含量最高的反式脂肪酸异构体均为11t C18:1。羊肉中9t C18:1、10t C18:1和11t C18:1的含量比较均衡,其它反刍动物产品中12t C18:1、13/14t C18:1、15t C18:1、16t C18:1的总量达到总反式脂肪酸含量的(25.9±1.8)%。坚果类食品中,TFA主要为t C18:1和9t12t C18:2,且9t12t C18:2含量约为总TFAs的10%。其它原料食物,如水果、蔬菜、畜禽肉、鱼虾及腌菜中TFAs含量极低。     

上海地区部分市售食品中反式脂肪酸含量与组成分析

目的了解上海地区部分市售食品中的反式脂肪酸(trans-fatty acids,TFAs)含量以及异构体组成,为开展TFAs的风险评估和食品选择提供参考。方法于2011年1～6月在上海市超市、面包店或快餐店中抽取具有代表性的9大类共106种市售食品,包括植物油、乳及乳制品、休闲食品、方便食品、快餐食品、饮料、小吃甜饼、调味品和畜禽肉及制品,采用银离子固相萃取(Ag+-SPE)结合气相色谱方法检测TFAs含量。结果抽检样品中的TFAs以反式油酸(t C18∶1)为主,反式多不饱和脂肪酸含量较少。除黑咖啡外,其余105种食品均检测到TFAs,其中,巧克力派的TFAs含量最高(1 711.58 mg/100 g)。反刍动物食品和含乳及乳制品的食品中11t C18∶1异构体含量较高(占总TFAs的53.9%～100.0%)。富含氢化油的休闲食品中9t C18∶1异构体含量较高(占总TFAs的14.3%～87.7%)。猪肉和牛肉经加工后TFAs含量有不同程度降低。结论市售食品中普遍检测到TFAs,食物成分和加工过程不同总TFAs含量及异构体组成存在较大差异,预包装休闲食品和西式甜饼店食品含有较多的TFAs。     

气相色谱法测定焙烤食品中反式脂肪酸含量

反式脂肪酸是一种具有反式构型的不饱和脂肪酸,摄入量过多会对人体健康造成一系列不良影响。采用气相色谱法测定、内标法定量,对面包、饼干、蛋糕等11种市售常见焙烤食品中的反式脂肪酸含量进行测定分析。试验结果表明,13种反式脂肪酸甲酯异构体的分离良好,11种样品中反式脂肪酸含量为0.10%～2.81%,其中丹麦小牛角面包最高,为2.81%;若以占脂肪的比例计,则反式脂肪酸含量为1.18%～10.75%,其中以trans C18∶1为主要的反式脂肪酸,占所测总反式脂肪酸含量的46.59%～80.65%。     

人造奶油中反式脂肪酸含量分析

采用氢氧化钠-甲醇对样品中的脂肪酸和反式脂肪酸进行甲酯化处理,气相色谱仪测定,以十一碳酸甘油三酯为内标进行定量。分析测定了国内5家知名焙烤企业抽检的41种不同用途的人造奶油中反式脂肪酸含量,通过分析发现:不同用途的人造奶油脂肪酸含量和组成有所差异,而反式脂肪酸的组成基本一致:主要是C18:1 6t、C18:19t、C18:1 11t和C18:2 9c12t、C18:2 9t12c。反式脂肪酸含量范围为0.271%反式脂肪酸含量(占总脂肪酸)8.245%。其中反式脂肪酸含量(占总脂肪酸)1%的共有35种,占总抽检数的85.4%;含量3%的有两种,占总抽检数的4.88%。本次研究较客观地反映了目前国内主流市场上人造奶油中反式脂肪酸含量情况,为国家风险管理部门进一步加强政策引导和宣传力度,引导消费者培养和强化消费前阅读营养标签的习惯提供数据依据。     

7类食品中反式脂肪酸含量的调查

对采集的7类76种食品中的反式脂肪酸(TFAS)异构体构成及其含量进行调查。采用气相色谱内标法测定反式脂肪酸(TFAS)含量。结果表明:68%样品中的TFAS含量≤0.3 g/100 g,29%样品的TFAS含量在0.3～2.0 g/100 g,只有3%样品的TFAS含量>2 g/100 g。除锅巴和膨化食品外,被检食品中的TFAS异构体的组成主要是以C18∶1t为主,其C18∶1 t总量占总TFAS含量的60%～96%,说明反式脂肪酸(TFAS)广泛存在于被检的各类食品中,除含人造奶油、代可可脂高的少数食品外,绝大多数食品中的TFAS含量水平不高。     

反棕榈油酸对人肝细胞脂质的影响

流行病学研究报道反刍动物代表性反式脂肪酸反棕榈油酸(9t16∶1)具有降低血脂的作用,为了进一步研究9t16∶1对细胞脂质代谢的影响,采用不同浓度反棕榈油酸作用于脂肪变性人肝细胞LO2,通过测定细胞存活率、细胞脂肪酸组成、脂质含量变化以及细胞氧化情况反映反棕榈油酸对脂质代谢的作用。结果表明:100μmol/L的9t16∶1作用于人肝细胞后饱和脂肪酸含量降低了34.89%,单不饱和脂肪酸含量升高了16.44%,多不饱和脂肪酸含量升高了30.50%;9t16∶1在人肝细胞内部分生物转化为11t18∶1和CLA,其转化率分别为17.50%和16.42%;9t16∶1显著降低脂肪变性人肝细胞甘油三酯和胆固醇含量,降低率分别为61.76%和37.80%;9t16∶1显著升高人肝细胞MDA水平(升高率为45.36%)和降低SOD活力(降低74.42%),促进细胞内脂质氧化。因此,反棕榈油酸可通过促进人肝细胞脂质氧化达到降低脂质堆积的作用。     

栉孔扇贝和海湾扇贝脂质及其脂肪酸组成分析

以栉孔扇贝和海湾扇贝为研究对象,采用Folch法提取两种扇贝肌肉和内脏中的总脂,并对其脂质和脂肪酸组成进行分析。结果表明:两种扇贝的肌肉总脂含量显著低于内脏,且肌肉总脂以磷脂为主,而内脏总脂以甘油三酯为主。两种扇贝的脂肪酸组成特征为多不饱和脂肪酸(PUFA)>饱和脂肪酸(SFA)>单不饱和脂肪酸(MUFA),其中,PUFA以n-3系列为主,主要为C20∶5n-3(16.58%~19.00%)和C22∶6n-3(11.49%~21.18%);肌肉中的n-3/n-6比值高于内脏,尤其C22∶6n-3含量显著高于内脏(P<0.01)。同时从两种扇贝中鉴定出6种脂肪醛二甲基缩醛(DMA),总量在7.77%~11.20%,并以C18∶0DMA(3.05%~6.89%)和C20∶1DMA(1.55%~4.25%)为主,且肌肉中DMA含量高于内脏,表明两种扇贝总脂中含有丰富的缩醛磷脂,肌肉总脂中的缩醛磷脂百分含量高于内脏。     

固相萃取-气相色谱法测定蒸制前后中华绒螯蟹性腺中甘油三酯和磷脂脂肪酸组成

采用固相萃取法(SPE)对中华绒螯蟹性腺脂质中的甘油三酯和磷脂进行分离纯化,采用棒状薄层色谱仪(TLC/FID)对纯化得到的脂质成分进行纯度鉴定,用气相色谱仪(GC)分别对蒸制前后的中华绒螯蟹性腺脂质中甘油三酯和磷脂的脂肪酸组成与变化进行分析。研究表明:纯化得到的甘油三酯纯度为98.29%,磷脂纯度为98.40%。雄蟹性腺中甘油三酯、磷脂含量分别为36.54%,1.99%;雌蟹性腺中分别为22.13%,4.71%;蒸制后甘油三酯、磷脂含量均有下降,且磷脂含量呈显著性下降。蒸制后性腺甘油三酯的脂肪酸含量变化不大,而磷脂的脂肪酸含量明显降低,特别是磷脂中一些多不饱和脂肪酸如C_(18:2n6c)、C_(18:3n3)、C_(20:4n6)、C_(20:5n3(和C_(22:6n3)呈极显著性下降,与蟹中醛类等关键挥发物质的形成呈正相关性。本结果为解析河蟹脂类来源关键香气物质的形成机制提供科学依据。     

Fatty Acid Composition and Triglyceride Structure of Corn Oil, Hydrogenated Corn Oil, and Corn Oil Margarine

Corn oil, hydrogenated corn oil and corn oil margarine were compared on the basis of fatty acid composition and triglyceride structure, including configurational isomerism of unsaturated fatty acids. Hydrogenated corn oil contained trans unsaturation and positional isomers not naturally found in corn oil. The β-position of triglycerides of hydrogenated corn oil was 85% occupied by trans octadecenoic acids (trans-18:1); that of corn oil was 70% occupied by linoleic acid. The proportion of cis octadecenoic acids (cis-18:1) in the β-position of the triglycerides was distinctly less in the hydrogenated corn oil than in corn oil, indicating a hydrogenation and/or a geometrical isomerization of cis-18:1 to trans-18:1 preferentially in the β-position, as compared with the α-positions. Chemical composition of corn oil margarine was intermediate between that of corn oil and that of hydrogenated corn oil.     

Trans18:1 and 18:2 isomers in blood plasma and milk fat of grazing cows fed a grain supplement containing solvent-extracted or mechanically extracted soybean meal

Thirty Holstein cows grazing mixed clover-grass pastures for 12 wk from May through July were fed a grain supplement containing solvent-extracted soybean meal (SES), or mechanically extracted soybean meal (MES) to determine whether differences in supplemental 18:2n6 fatty acid intake altered secretion of unsaturated fatty acids. Groups of 10 cows each were fed in two equal feedings a supplement (7.3 kg/d) containing ground corn plus either 1.8 kg of SES, 2.2 kg of MES, or 2.2 kg of MES plus 30 g of methionine hydroxy analog (Alimet; MESM). Fatty acid content (% of DM) of grass and clover in pastures averaged 1.9 and 1.5%, respectively. Concentration of 18:3n3 was higher in grass compared with clover (532 vs. 454 mg/g of total fatty acids). Yield of milk (32 kg/d average) and milk components did not differ by supplements. Total blood plasma fatty acids (mg/ml) during wk 4 were higher due to MESM (1.0) compared with MES (0.6) or SES (0.6). Cows fed MESM or MES had greater concentrations of 18:2n6, trans11-18:1, and cis9,trans11-18:2 in plasma compared with cows fed SES. The additional trans11-18:1 was found exclusively in plasma triglycerides, whereas the additional cis9,trans11-18:2 was found in plasma phospholipids and free fatty acids. Daily yields of 18:2n6, trans11-18:1 and cis9,trans11-18:2 in milk fat were greater for cows fed MES or MESM compared with SES. Results indicate yields of trans11-18:1, cis9, trans11-18:2, 18:2n6, and 18:3n3 in milk fat of pasture-fed cows were enhanced by feeding a grain supplement containing mechanically extracted, rather than solvent-extracted, soybean meal.     

The analysis of polyunsaturated fatty acids in meat by capillary gas-liquid chromatography

Polyunsaturated fatty acids (PUFA) of lean meat from domesticated and wild ruminants (cattle, sheep, goat, sambar deer and buffalo) and non-ruminants (pig, horse and kangaroo) have been examined by capillary gas-liquid chromatography. Ten different PUFA were found in all specimens with linoleic acid accounting for at least 50% of the total, and arachidonic and linolenic acids being the next most abundant. The total PUFA content for the ruminants ranged from 9 % in beef to 31 % in sambar deer and for the non-ruminants from 25 % in pig to 43 % in horse. In all species the meat phospholipids ( PL ) were rich in PUFA (range 24–46% of PL fatty acids), whereas the triglycerides were relatively more saturated (PUFA content range 2–17%). Overall, horse and kangaroo meat had the combination of lowest fat and highest PUFA content, whilst beef and sheep had the highest fat and lowest PUFA content. These results indicate that significant reductions in total fat intake and increases in the proportion of polyunsaturated fat in the diet could be achieved without necessarily requiring a diet low in meat.     

TRANS FATTY ACID CONTENT OF SOME FOOD PRODUCTS IN POLAND

The fatty acid composition of chips, cakes and ice creams was determined with particular attention to their trans fatty acid content. The trans C18:1 content was determined by a combined capillary gas-liquid chromatography (GLC) and silver thin-layer chromatography (Ag-TLC). Six of ten types of chips examined contained more than 10% trans C18:1 (in the range of 10.3 to 17.3% of the total fatty acids), and the other four had below 0.5%. In the lipids of cakes trans C18:1 isomers occurred at 1.49 to 41.44% and only four types of cakes contained less than 5% of trans C18:1. The cis-trans and trans-cis C18:2 isomers were present among the fatty acids of the majority of chips and cakes investigated. Six types of chips contained trans-trans C18:2 in the 1.2–1.6% range. Trans fatty acids were absent in the lipids of 6 types of ice cream, but two types contained 11.3 and 19.4% trans C18:1.     

Evaluation of the Impact of Ruminant Trans Fatty Acids on Human Health: Important Aspects to Consider

The definition and evaluation of trans fatty acids (TFA) with regard to foodstuffs and health hazard are not consistent. Based on the current situation, the term should be restricted only to TFA with isolated double bonds in trans-configuration. Conjugated linoleic acids (CLA) should be separately assessed. Ideally, the origin of the consumed fat should be declared, i.e., ruminant TFA (R-TFA) and industrial TFA (non-ruminant; I-TFA). In ruminant fat, more than 50% of R-TFA consists of vaccenic acid (C18:1 t11). In addition, natural CLA, i.e., c9,t11 CLA is also present. Both are elevated in products from organic farming. In contrast to elaidic acid (t9) and t10, which occur mainly in partially hydrogenated industrial fat, t11 is partially metabolized into c9,t11 CLA via Δ9-desaturation. This is the major metabolic criterion used to differentiate between t11 and other trans C18:1. t11 indicates health beneficial effects in several studies. Moreover, CLA in milk fat is associated with the prevention of allergy and asthma. An analysis of the few studies relating to R-TFA alone makes clear that no convincing adverse physiological effect can be attributed to R-TFA. Only extremely high R-TFA intakes cause negative change in blood lipids. In conclusion, in most European countries, the intake of R-TFA is assessed as being low to moderate. Restriction of R-TFA would unjustifiably represent a disadvantage for organic farming of milk.     

Conjugated linoleic acid and C18:1 isomers content in milk fat of sheep and their transfer to Pecorino Toscano cheese

The aim of the study was to evaluate the transfer of conjugated linoleic acid (CLA) and of C18:1 isomers from sheep milk to Pecorino Toscano protected denomination of origin cheese and to monitor the stability of these fatty acids during ripening. The total content of C18:1 fatty acids was not affected by milk treatment but there were changes in the isomers profile. In particular, the milk trans11 C18:1 decreased with pasteurization and after starter culture addition. In contrast, trans10 C18:1 and cis9, trans11 C18:2 were enhanced by the thermal treatment of milk. The fatty acid profile of cheese reflected that of milk used for cheese making with the exception of the C18:1 and CLA isomer profile. The cheese ripening affected the percentage of cis9, trans11 C18:2, which increased more than 10% on total content of CLA.     

Innovations in beef production systems that enhance the nutritional and health value of beef lipids and their relationship with meat quality

Consumers are becoming more aware of the relationships between diet and health and this has increased consumer interest in the nutritional value of foods. This is impacting on the demand for foods which contain functional components that play important roles in health maintenance and disease prevention. For beef, much attention has been given to lipids. This paper reviews strategies for increasing the content of beneficial omega-3 polyunsaturated fatty acids (PUFA) and conjugated linoleic acid (CLA) and reducing saturated fatty acids (SFA) in beef. Particular attention is given to intramuscular fat (IMF) and the relationships between fatty acid composition and key meat quality parameters including colour shelf life and sensory attributes. Despite the high levels of ruminal biohydrogenation of dietary PUFA, nutrition is the major route for increasing the content of beneficial fatty acids in beef. Feeding grass or concentrates containing linseed (rich in α-linolenic acid, 18:3n-3) in the diet increases the content of 18:3n-3 and its longer chain derivative eicosapentaenoic acid (EPA, 20:5n-3) in beef muscle and adipose tissue, resulting in a lower n-6:n-3 ratio. Grass feeding also increases docasahexaenoic acid (DHA, 22:6n-3). Feeding PUFA rich lipids which are protected from ruminal biohydrogenation result in further enhancement of the PUFA in meat with concomitant beneficial improvements in the ratio of polyunsaturated:saturated fatty acids (P:S ratio) and n-6:n-3 ratio. The main CLA isomer in beef is CLA cis-9, trans-11 and it is mainly associated with the triacylglycerol lipid fraction and therefore is positively correlated with level of fatness. The level of CLA cis-9, trans-11 in beef is related to (1) the amount of this isomer produced in the rumen and (2) synthesis in the tissue, by delta-9 desaturase, from ruminally produced trans vaccenic acid (18:1 trans-11; TVA). Feeding PUFA-rich diets increases the content of CLA cis-9, trans-11 in beef. Trans-fatty acids in foods are of rising importance and knowledge of the differential effects of the individual trans isomers is increasing. TVA is the major trans 18:1 isomer in beef and as the precursor for tissue CLA in both animals and man should be considered as a neutral or beneficial trans-isomer. Increasing the content of n-3 PUFA in beef can influence colour shelf life and sensory attributes of the meat. As the content of n-3 PUFA increases then sensory attributes such as "greasy" and "fishy" score higher and colour shelf life may be reduced. Under these situations, high levels of vitamin E are necessary to help stabilise the effects of incorporating high levels of long chain PUFA into meat. However, grass feeding not only increases n-3 PUFA and CLA but, due to its high content of vitamin E, colour shelf life is improved. It is evident that opportunities exist to enhance the content of health promoting fatty acids in beef and beef products offering opportunities to add value and contribute to market differentiation. However, it is imperative that these approaches to deliver "functional" attributes do not compromise on the health value (lipoperoxidation) or the taste of beef products.     

Milk composition and apparent digestibilities of dietary fatty acids in lactating dairy cows abomasally infused with Cis or Trans fatty acids

Fat supplementation of diets for dairy cows produces changes in nutrient supply and milk composition. The effect of abomasal infusion of either cis-C18:1 or trans-C18:1 fatty acid isomers on the digestibility of fatty acids and milk composition was determined in lactating dairy cows. Six multiparous midlactation Holstein cows were used and fed a control diet containing 50% forage and 50% concentrate. Treatments were (per day): no infusion, infusion of a 630-g fat mixture high in cis-C18:1 isomers, and infusion of a 623-g fat mixture high in trans-C18:1 isomers using two 3 x 3 Latin squares with 4-wk experimental periods. Fat infusion did not affect total dry matter intake and increased apparent digestibilities of total fatty acids. Apparent digestibilities of C18 fatty acids were directly related to the number of double bonds within isomers, and cis-C18:1 isomers were slightly more digestible than trans-C18:1 isomers. The lower yield of C12:0, C14:0, and C16:0 fatty acids in milk fat and higher milk citrate observed when cows were infused with trans-C18:1 suggests a depressed de novo milk fatty acid synthesis. Effects of trans infusion on milk fat were independent of ruminal fermentation, fatty acid apparent absorption, and fatty acid plasma concentrations. Lower milk protein yield in cows infused with fat may have been caused by a decrease in milk protein synthesis.     

EFFECTS OF DIETARY 18:3 N-3 TRANS ISOMERS ON THE Δ6 DESATURATION OF α-LINOLENIC ACID

Trans isomers of polyunsaturated fatty acids (PUFA) are formed during heat treatment of oils. In the present work, the effect of dietary geometrical isomers of α-linolenic acid (18:3 n-3) on the Δ6 desaturation of all cis 18:3 n-3 was investigated, using rat liver microsomes. The desaturation rates were higher in microsomes from animals fed a cis n-3 deficient diet, as compared to those from the control group or those from rats fed 18:3 n-3 and its trans isomers. These data and the incorporation of long chain trans PUFA in microsomal lipids suggest that geometrical isomers of 18:3 n-3 are probably slowly desaturated and elongated into long chain trans polyunsaturated fatty acids compared to 18:3 n-3.