银离子固相萃取法测定反刍动物反式脂肪酸异构体含量

利用氨丙基硅胶柱从反刍动物脂质中分离甘油三酯和磷脂,以氢化大豆油作为对照。采用银离子固相萃取柱分离甘油三酯和磷脂中反式脂肪酸异构体,气相色谱仪测定反式脂肪酸含量。结果显示:在3种反刍动物脂质中检测出trans-16:1,trans-18:1和trans18:2 3类反式脂肪酸,其中总脂质和甘油三酯总反式脂肪酸含量最高的是羊肉脂质,分别占总脂肪酸的7.64%和7.38%;磷脂中总反式脂肪酸最高的是牛肉脂质,占总脂肪酸的5.89%。银离子固相萃取柱能够从反刍动物脂质中分离出9种trans18:1异构体,其中含量最高的是11t18:1,分别为总脂质、甘油三酯和磷脂trans18:1的30.33%~39.03%,38.08%~45.09%和27.10%~44.47%。通过PLS-DA分析3种反刍动物反式脂肪酸异构体之间的差异,羊肉脂质中甘油三酯中的9t18:1和磷脂中的11t18:1含量均显著高于牛奶脂质和牛肉脂质(P<0.05);牛肉脂质中磷脂中的9t18:1和15t18:1含量均显著高于牛奶脂质和羊肉脂质(P<0.05);牛奶脂质磷脂中的12t18:1和16t18:1的含量均显著高于牛肉脂质和羊肉脂质(P<0.05)。反刍动物磷脂中的反式脂肪酸异构体有较大差异。     

11种品牌玉米油脂肪酸及异构体的主成分分析

对市售的11种品牌玉米油开展了脂肪酸(包括脂肪酸及其异构体)组成与含量的调查研究。采用气相色谱技术,结合主成分分析法,分析了不同品牌玉米油中脂肪酸的差异性和相关性。结果表明,11种品牌玉米油中共鉴定出19种脂肪酸,包括7种饱和脂肪酸,5种不饱和脂肪酸,6种反式脂肪酸(TFAs)和1种共轭亚油酸(t,t-CLAs),平均含量分别为14.18×10~(-2) g/g,80.32×10~(-2) g/g,1.47×10~(-2) g/g和0.23×10~(-2) g/g;其中,亚油酸(C18:2-9c12c)、油酸(C18:1-9c)和棕榈酸(C16:0)依次是玉米油中含量最多的3种脂肪酸;不同品牌玉米油中脂肪酸含量存在显著性差异(p0.05)。主成分分析揭示了不同品牌玉米油在脂肪酸含量上的相似性、差异性及脂肪酸之间相关程度,TFAs和CLAs正相关程度高。本研究为评价市售玉米油脂肪酸品质特征提供了较为全面的数据支撑。     

粟米油中脂肪酸及其主成分亚油酸的分析

高效液相色谱法对粟米油脂肪酸的组成和主成分亚油酸进行定量分析。采用索氏提取法从玉米胚芽中提取粟米油,并对粟米油中脂肪酸进行甲酯化处理,利用气相色谱- 质谱法对其脂肪酸组成进行鉴定。色谱柱：KromasilC18;流动相为异丙醇:乙腈=35:65;柱温：25℃;205nm 检测波长条件下对亚油酸进行测定。结果表明：由粟米油中分离鉴定出8 种脂肪酸,脂肪酸的主要组成是不饱和脂肪酸,不饱和脂肪酸占74.94%,主要成分为亚油酸和油酸,其中亚油酸为46.33%,油酸为28.01%。亚油酸变异系数小于1.35%,回收率为98.8%～109.1%。本方法简便、准确,适合粟米油中亚油酸含量的分析。     

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。     

Milk fat responses to a change in diet fermentability vary by production level in dairy cattle

The effects of dietary starch fermentability on plasma metabolites and hormones, milk production, and milk fatty acid profile were evaluated in a crossover study. Thirty-two multiparous Holstein cows (121 +/- 48 d in milk, 41 +/- 9 kg/d 3.5% fat-corrected milk [FCM]; mean +/- SD) were randomly assigned to treatment sequence and were fed a diet intermediate to the treatments during an initial 21-d period. Treatments were dry ground corn grain (DG) and high moisture corn (HM) harvested from the same field. Treatment periods were 14 d, with the final 4 d used for data and sample collection. Diets included corn silage and alfalfa haylage at a 2:1 ratio and were ~26% neutral detergent fiber, 16.5% crude protein, 32% starch, and 3.5% fatty acids. High moisture corn increased plasma glucose, nonesterified fatty acid, and triglyceride concentrations, but treatment had no consistent effect on yield of milk or FCM. High moisture corn increased trans C(18:1) concentrations at an increasing rate as production level decreased across cows, and milk fat depression was evident in cows below approximately 40 kg/d FCM yield. In contrast, production level had little influence on milk trans C(18:1) concentration for DG. Milk trans C(18:1) concentration was negatively correlated with milk fat concentration, as was trans-9 C(18:1), trans-10 C(18:1), and cis-9, trans-11 C(18:2). Concentration of trans-10, cis-12 C(18:2) was not correlated with milk fat concentration. Production level may influence biohydrogenation patterns and trans C(18:1) production because of differences in rumen environment; rumen pH and dilution rate can alter metabolism and populations of rumen microbes. Diets with highly fermentable starch sources and without supplemental dietary polyunsaturated fatty acids can induce milk fat depression in lower-producing cows, likely because of increased production of trans C(18:1) fatty acids.     

玉米油的制备及脂肪酸的分析

以辽宁地区玉米种子为原料制备玉米油。对玉米油进行甲酯化处理,以气相色谱-质谱联用仪进行了分析,共分离鉴定出7种脂肪酸。其中主要成分为:棕榈酸、油酸和亚油酸。用高效液相色谱法对亚油酸进行了定量分析。     

凝胶油基人造奶油质地和流变性能

凝胶油作为潜在的能够替代传统氢化奶油的新方法,具有低饱和脂肪酸和零反式脂肪酸的优势,所受关注 度越来越高。本实验以精炼大豆油为基料油,β-谷甾醇和卵磷脂等比例混合物作为复合凝胶剂,制备得到凝胶油基 人造奶油。主要研究了凝胶剂质量分数和水分体积分数对凝胶油基人造奶油质地、流变学性能、微观网络结构和结 晶度的影响。结果表明：当水分体积分数提高时,能够在更低的凝胶剂质量分数下形成均相人造奶油体系;随着凝 胶剂质量分数和水分体积分数的增加,人造奶油的硬度和弹性增大;样品网络结构和结晶度的分析结果表明,随着 凝胶剂质量分数和水分体积分数的增加,人造奶油的结晶度增加,微观三维网络结构更加完整,油-水两相接触面 积变大,最终使得人造奶油体系结构更加均匀和稳定,硬度和弹性也更大。     

Effect of cereal grain and fibre supplements on the fatty acid composition of milk fat of grazing dairy cows in early lactation

Two experiments were undertaken to determine the effects of cereal grain and fibre (hay or straw) supplements on the fatty acid composition of milk fat of grazing dairy cows in early lactation. In both experiments, grain supplements significantly increased (P < 0.05) the proportion of the endogenously synthesized 10:0-16:0 fatty acids. Of the C18 acids, the proportion of 18:0 and 18:3 was significantly decreased (P < 0.05) by grain supplementation, while that of 18:2 was significantly increased (P < 0.05). Irrespective of diet, 18:1 trans-11 was the most dominant trans 18:1 isomer in milk fat. In the first experiment, the proportions of the 18:1 trans-11 isomer and conjugated linoleic acid (CLA, 18:2 cis-9, trans-11) were highest for the pasture-only diets, and significantly (P < 0.05) decreased with grain supplementation. The opposite result was observed in the second experiment, conducted in a different dairy region, suggesting that factors such as the quality of pasture on offer and the physiological state of the cow could affect the content of CLA and trans fatty acids in milk fat. In both experiments, there was a significant positive linear relationship between CLA and 18:1 trans-11. Fibre supplements had little effect on the fatty acid composition of the milk.     

煎炸油在煎炸过程中脂肪酸组成的变化

以大豆油、棉籽油、棕榈液油和氢化油作为煎炸油,分别进行薯条和鸡翅的煎炸实验。结果表明：在煎炸过程中,各种煎炸油的脂肪酸含量均会发生一定的变化。采用C18:2/C16:0比值变化作为研究煎炸油脂肪劣变的指标,氢化油煎炸过程中C18:2/C16:0比值减少的程度最小(P＜0.05),证明其煎炸过程中脂肪酸的稳定性最好。但对于反式脂肪酸含量变化来说,均没有显著增加(P＞0.05),其中氢化油的反式脂肪酸含量从煎炸前的10.39%降低到煎炸后的6.66%,变化显著(P＜0.05),不过高反式脂肪酸含量的煎炸油在煎炸后其反式脂肪酸含量还保持在较高水平。     

Production of conjugated fatty acids by lactic acid bacteria

Conjugated fatty acids have attracted much attention as a novel type of biologically beneficial functional lipid. Some isomers of conjugated linoleic acid (CLA) reduce carcinogenesis, atherosclerosis, and body fat. Considering the use of CLA for medicinal and nutraceutical purposes, a safe isomer-selective process is required. The introduction of biological reactions for CLA production could be an answer. We screened microbial reactions useful for CLA production, and found several unique reactions in lactic acid bacteria. Lactic acid bacteria produced CLA from linoleic acid. The produced CLA comprised a mixture of cis-9,trans-11-octadecadienoic acid (18:2) and trans-9,trans-11-18:2. Lactobacillus plantarum AKU 1009a was selected as a potential CLA producer. Using washed cells of L. plantarum AKU 1009a as a catalyst, CLA production from linoleic acid reached 40 mg/ml under the optimized conditions. The CLA-producing reaction was found to consist of two successive reactions, i.e., hydration of linoleic acid to 10-hydroxy-12-octadecenoic acid and dehydrating isomerization of the hydroxy fatty acid to CLA. On the basis of these results, the transformation of hydroxy fatty acids by lactic acid bacteria was investigated. Lactic acid bacteria transformed ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) to CLA (a mixture of cis-9,trans-11-18:2 and trans-9,trans-11-18:2). Castor oil, which is rich in the triacylglycerol form of ricinoleic acid, was also found to act as a substrate for CLA production by lactic acid bacteria with the aid of lipase-catalyzed triacylglycerol hydrolysis. L. plantarum AKU 1009a produced conjugated trienoic fatty acids from alpha- and gamma-linolenic acid. The trienoic fatty acids produced from alpha-linolenic acid were identified as cis-9,trans-11,cis-15-octadecatrienoic acid (18:3) and trans-9,trans-11,cis-15-18:3. Those produced from gamma-linolenic were cis-6,cis-9,trans-11-18:3 and cis-6,trans-9,trans-11-18:3. The conjugated trienoic fatty acids produced from alpha- and gamma-linolenic acid were further saturated by L. plantarum AKU 1009a to trans-10,cis-15-18:2 and cis-6,trans-10-18:2, respectively.     

Conjugated linoleic acid and vaccenic acid in rumen, plasma, and milk of cows fed fish oil and fats differing in saturation of 18 carbon fatty acids

The objective of this study was to examine the effect of feeding fish oil (FO) along with fat sources that varied in saturation of 18 carbon fatty acids (high stearic, high oleic, high linoleic, or high linolenic acids) on rumen, plasma, and milk fatty acid profiles. Four primiparous Holstein cows at 85 d in milk (+/- 40) were assigned to 4 x 4 Latin squares with 4-wk periods. Treatment diets were 1) 1% FO plus 2% commercial fat high in stearic acid (HS); 2) 1% FO plus 2% fat from high oleic acid sunflower seeds (HO); 3) 1% FO plus 2% fat from high linoleic acid sunflower seeds (HLO); and 4) 1% FO plus 2% fat from flax seeds (high linolenic; HLN). Diets were formulated to contain 18% crude protein and were composed of 50% (dry basis) concentrate mix, 25% corn silage, 12.5% alfalfa silage, and 12.5% alfalfa hay. Milk production, milk protein percentages and yields, and dry matter intake were similar across diets. Milk fat concentrations and yields were least for HO and HLO diets. The proportion of milk cis-9, trans-11 conjugated linoleic acid (CLA; 0.71, 0.99, 1.71, and 1.12 g/100 g fatty acids, respectively), and vaccenic acid (TVA; 1.85, 2.60, 4.14, and 2.16 g/100 g fatty acids, respectively) were greatest with the HLO diet. The proportions of ruminal cis-9, trans-11 CLA (0.09, 0.16, 0.18, and 0.16 g/100 g fatty acids, respectively) were similar for the HO, HLO, and HLN diets and all were higher than for the HS diet. The proportions of TVA (2.85, 4.36, 8.69, and 4.64 g/100 g fatty acids, respectively) increased with the HO, HLO, and HLN diets compared with the HS diets, and the increase was greatest with the HLO diet. The effects of fat supplements on ruminal TVA concentrations were also reflected in plasma triglycerides, (2.75, 4.64, 8.77, and 5.42 g/100 g fatty acids, respectively); however, there were no differences in the proportion of cis-9, trans-11 CLA (0.06, 0.07, 0.06, and 0.07 g/100 g fatty acids, respectively). This study further supports the significant role for mammary delta-9 desaturase in milk cis-9, trans-11 CLA production.     

高分辨率反式脂肪酸测定方法的建立及市售食用油反式脂肪酸的测定

本文建立了高分辨率的反式脂肪酸测定方法,并考察了市售食用油的反式脂肪酸含量及其种类的情况。结果表明:采用高极性的色谱柱HP-88在优化后色谱条件下,可以实现4种亚油酸异构体、8种亚麻酸异构体、37种常见脂肪酸良好的色谱分离,而且反式脂肪酸与常见的顺式脂肪酸在同时检测条件下出峰时间不重叠,可以进行高分辨率的脂肪酸包括反式脂肪酸组成分析;市售主要品种的食用油都存在一定量的反式脂肪酸,其中调和油、花生油、大豆油含有2~3%的反式脂肪酸(反式亚麻酸含量在1.5~2%之间);玉米油和葵花籽油中反式亚油酸的含量在0.7~2%之间;稻米油的反式脂肪酸的含量最高,接近4%;橄榄油和山茶油的反式脂肪酸含量一般在0.5%以下;各油样的反式脂肪酸异构体的种类也存在区别。     

反式脂肪酸安全问题辨析

针对我国反式脂肪酸安全问题宣传中存在的问题,从氢化油、植物黄油等产品的定义和发展历史出发,释义了反式脂肪酸,阐述了反式脂肪酸与人体健康的关系,并初步评估了我国民众反式脂肪酸摄入情况,旨在开展对反式脂肪酸安全问题的科学理性讨论,普及和提高公众对反式脂肪酸问题的科学理性认识,指导食品消费和生产。     

Monensin by fat interactions on trans fatty acids in cultures of mixed ruminal microorganisms grown in continuous fermentors fed corn or barley

In previous studies, monensin (M) and unsaturated plant oils independently increased trans fatty acid concentrations in cultures of mixed ruminal microorganisms. This study was conducted to determine if combining M with plant oil yielded interactions on trans fatty acid concentrations in cultures of mixed ruminal microorganisms or their effects were additive. Four continuous fermentors were fed 14 g of dry feed per day (divided equally between two feedings), consisting of alfalfa hay pellets (30% of DM) and either a high corn (HC) or a high barley (BB) concentrate (70% of DM) in each of two fermentors. Within each grain type, one fermentor was supplemented with M (25 ppm), and the other fermentor was supplemented with 5% soybean oil (SBO) during d 5 to 8. Monensin and SBO were added together in all fermentors during d 9 to 12. Samples were taken at 2 h after the morning feeding on the last day of each period and analyzed for fatty acids by gas-liquid chromatography. A second run of the fermentors followed the same treatment sequence to give additional replication. Average pH across all treatments was 6.15, which was reduced by M but not affected by SBO. Monensin reduced the ratio of acetate to propionate (A:P), which averaged 2.03 across all treatments; fat decreased A:P in cultures not receiving M but increased it in the presence of M. Monensin and SBO altered the concentration of several trans fatty acids, but the only interaction was a grain x M x SBO interaction for trans-10 C18:1. The increase in trans-10 C18:1 by the M and SBO combination exceeded the sum of increases in trans-10 C18:1 for each individual feed additive, but only for KB. For the HC diet, M increased trans-10 C18:1 more than fat alone and more than the M and SBO combination. The results of this study show that M and SBO effects are additive for all trans FA except for trans-10 C18:1. In the case of trans-10 C18:1, M and SBO interacted to give higher trans-10 C18:1 concentrations in ruminal contents than would be expected simply by adding their individual effects, but only for HB. Because some trans fatty acid isomers have been associated with milk fat depression in dairy cows, these results suggest more severe depressions in milk fat content when cows are fed M along with unsaturated plant oils.     

Endogenous synthesis of cis-9, trans-11 conjugated linoleic acid in dairy cows fed fresh pasture

New Zealand Holstein-Friesian cows (n = 4) were used to quantify the importance of endogenous synthesis of cis-9, trans-11 conjugated linoleic acid (CLA) via Delta(9)-desaturase in cows fed a fresh pasture diet. The experiment was a 4 x 4 Latin square design with treatments arranged in a 2 x 2 factorial. Treatments lasted 4 d and were pasture only, pasture plus sterculic oil, pasture plus sunflower oil, and pasture plus sunflower oil plus sterculic oil. Abomasal infusion of sterculic oil inhibited Delta(9)-desaturase and decreased the concentration of cis-9, trans-11 CLA in milk fat by 70%. Using the changes in cis-9 10:1, cis-9 12:1 and cis-9 14:1 to correct for incomplete inhibition of Delta(9)-desaturase, a minimum estimate of 91% of cis-9, trans-11 CLA in milk fat was produced endogenously in cows fed fresh pasture. Dietary supplementation of a pasture diet with sunflower oil increased the proportion of long chain fatty acids in milk fat; however, the increase in vaccenic acid concentration was small (18%) and there was no increase in cis-9, trans-11 CLA concentration. Overall, results show that endogenous synthesis is responsible for more than 91% of the cis-9, trans-11 CLA secreted in milk fat of cows fed fresh pasture. However, the failure of plant oil supplements to increase the concentration of cis-9, trans-11 CLA in milk fat from pasture-fed cows requires further investigation.     

Effect of diet supplementation with sunflower oil on milk production, fatty acid profile and ruminal fermentation in lactating dairy ewes

The aim of this research was to enhance the nutritional quality of ewe milk fat by increasing potentially healthy fatty acids (FA) through diet supplementation with unprotected oil rich in linoleic acid, and without detrimental effects on animal performance. Twenty-four ewes were assigned to two high concentrate diets, control or supplemented with 6% sunflower oil (SO), for 4 weeks. No differences between treatments were found in milk production and dry matter intake. Although the SO diet increased milk fat percentage and tended to reduce milk protein concentration, it did not affect milk fat, protein or total solid yield. Most of the modifications in milk FA composition were addressed toward a potentially healthier profile: a decrease in C12:0 to C16:0 and a remarkable increase in the contents of cis-9 trans-11 C18:2 (from 0.94 to 3.60 g/100 g total FA) and trans-11 C18:1 (from 2.23 to 8.61 g/100 g total FA). Furthermore, the levels reached were maintained throughout the period monitored. However, the SO diet increased other trans C18:1 isomer percentages, too. The lack of differences between treatments in the in vitro ruminal fermentation parameters, studied with batch cultures of rumen microorganisms, would indicate no negative effects on ruminal fermentation.     

Enzymatic Production of Trans-Free Hard Fat Stock from Fractionated Rice Bran Oil, Fully Hydrogenated Soybean Oil, and Conjugated Linoleic Acid

ABSTRACT:  Rice bran oil (RBO) was fractionated into 2 phases, solid (S-RBO) and liquid (L-RBO), using acetone at –18 °C and the weight yield of each S-RBO and L-RBO was 45.5% and 54.5%, respectively. Then, trans -free hard fat was synthesized from trans -free substrate of S-RBO and fully hydrogenated soybean oil (FHSBO) at different molar ratios (S-RBO : FHSBO; 1 : 1, 1 : 1.5, 1 : 2, and 1 : 3) with Lipozyme TL IM lipase (10% of total substrate). Conjugated linoleic acid (CLA, 20% of total substrate) was used as functional fatty acids for the production of trans- free hard fat. After fatty acid analysis, CLA (12.2% to 14.2%) was found on the triacylglycerol (TAG) backbone of the interesterified products along with stearic (37.6% to 49%), palmitic (15% to 17.9%), and oleic acids (13.3% to 19.2%). The interesterified product contained higher level of saturated fatty acid (62.6% to 70.1%) at sn -2 position. Total tocopherols (α-, γ-, and δ-; 1.4 to 2.6 mg/100 g) and phytosterols (campesterol, stigmasterol, and β-sitosterol; 220.5 to 362.7 mg/100 g) were found in the interesterified products. From DSC results, solid fat contents of the interesterified products (S-RBO : FHSBO 1 : 1, 1 : 1.5, 1 : 2, and 1 : 3) at 25 °C were 23.1%, 27%, 30.1%, and 44.9%. The interesterified products consisted mostly of β' form crystal with a small portion of β form. The interesterified product (S-RBO : FHSBO 1 : 1.5) was softer than the physical blend but slightly harder than commercial shortenings as measured by texture analyzer. Thus, trans- free hard fat stock, which may have a potential functionality could be produced with various physical properties.     

Milk production and composition from cows fed high oil or conventional corn at two forage concentrations

Twelve multiparous Holstein cows (63 +/- 24 d in milk) were used in a replicated 4 x 4 Latin square with 28-d periods to evaluate conventional and high oil corn grains when fed at two different forage-to-concentrate ratios. Dietary treatments consisted of conventional or high oil corn supplementing a diet with a 25:25:50 mixture of corn silage: alfalfa: concentrate mix, or a high forage diet with a 30:30:40 mixture of corn silage: alfalfa: concentrate mix. Dry matter intake (28.1, 28.7, 26.9, and 26.2 kg/d for normal diets with conventional and high oil corn, and high forage diets with conventional and high oil corn, respectively) and milk yields (36.8, 37.2, 35.5, and 35.2 kg/d) were similar for conventional and high oil corn diets and were lower with the high forage diet, regardless of corn source. Milk fat concentrations were greater when cows were fed diets containing 60% forage (4.03 vs. 3.88%, for the 60 and 50% forages, respectively), but milk protein concentrations were not affected by forage content. Corn source did not affect milk fat or protein concentrations. Long-chain fatty acid concentrations, unsaturated fatty acid concentrations, and total 18:1 fatty acid concentrations were greater when cows were fed high oil corn but were unaffected by forage content of the diet. Concentrations of transvaccenic acid (0.58, 0.81, 0.62, and 0.69 g/100 g of fatty acids) and cis-9, trans-11 conjugated linoleic acid (0.28, 0.39, 0.32, and 0.33 g/100 g of fatty acids) were greater when cows were fed high oil compared with conventional corn when fed 50% forage but were similar for both corn sources at 60% forage. Total n-3 fatty acids were not affected by corn source or forage content. High forage diets decreased milk production and increased milk fat concentration. Feeding high oil corn increased concentrations of long-chain, unsaturated, transvaccenic, and conjugated linoleic fatty acids in milk; however, production of transvaccenic and conjugated linoleic acids were attenuated by high forage diet.     

玉米胚芽油脂肪酸衍生化工艺

以玉米胚芽油为原料,对其中亚油酸进行酯化衍生化,实现亚油酸的富集。分别考察碱用量、反应时间、反应温度及酸化程度对水解反应和H2SO4-甲醇溶液体积分数、用量、反应时间和温度对酯化反应的影响。结果表明：醇油比(95%乙醇-玉米胚芽油,mL/g)为2:1,KOH用量为玉米胚芽油皂化当量的1.1倍、80℃水浴回流100min时,水解反应最完全,酸值最大为207.85mg KOH/g,所得脂肪酸在催化剂5% H2SO4-甲醇溶液用量为5mL/g、70℃水浴30min条件下甲酯化反应最完全,气相色谱检测甲酯化程度为100%。经尿素包合进行富集得到纯度为96.98%的亚油酸。     

Short communication: influence of dietary tallow and fish oil on milk fat composition

Four midlactation Holstein cows in a 4 x 4 Latin square design were fed one of four diets that contained 3% added fat (dry matter basis) as 100:0, 67:33, 50:50, or 33:67 tallow:fish oil. Feed intake and yield and composition of milk were not affected by treatment. The proportion of fatty acids 18:0 and cis-18:1 decreased and trans-18:1, conjugated linoleic acid, 18:3, 20:4, and 20:5 increased in milk fat with increasing fish oil. The efficiency of transferring dietary 20:5 and 22:6 to milk fat was < 7%.