高效液相色谱法测定亚油酸甲酯含量

建立一种高效液相色谱测定亚油酸甲酯含量的方法。采用IntertsilO D S-SP柱,紫外检测器,检测波长为243 nm ,流动相为甲醇－水（体积比为95∶5）混合液,流速为0.8 m L/m in,进样体积为20μL,柱温为30℃。结果可知,亚油酸甲酯质量浓度和峰面积的线性回归方程是y=（2E＋06）x-43628,R 2=0.9999,线性范围是0～4.16 g/L,平均加样回收率为99.92%。     

Suppressive effect of defatted rice bran on the oxidation of methyl linoleate

The bran collected at each of the five steps of milling yields (98–100%, 96–98%, 94–96%, 92–94% and 90–92%) was defatted. Defatted rice bran (DRB) was added to methyl linoleate (ML) under various conditions, and its suppressive effect on lipid oxidation was kinetically evaluated to investigate the effective use of surplus rice bran. The rate constant, k, empirically evaluated by the Weibull equation for the oxidation of ML with DRB, was lower than that without DRB and decreased with increasing the maximum milling yield of added DRB. The oxidation of ML strongly depended on the added amount of DRB, but the k value was almost constant for a specific amount of DBR added to ML. The dependency of the k value on relative humidity was weak, regardless of the addition of DRB. The difference between the k values for oxidation processes of ML, with and without DRB, increased with increasing temperature.     

基于气相色谱法的油酸甲酯和亚油酸甲酯热氧化降解特性研究

利用气相色谱法分别测定油酸甲酯和亚油酸甲酯在不同温度下的氧化曲线,同时采用微分法和积分法对热氧化降解反应方程的参数进行了计算,进而确定了反映油酸甲酯和亚油酸甲酯热氧化降解历程的宏观反应动力学方程。微分法动力学分析结果表明:油酸甲酯热氧化降解反应的平均反应级数为1.37,活化能为5.48 k J/mol,反应动力学模型为rA=-dcA/dt=7.06exp(-5.48/RT)c1.37A;亚油酸甲酯热氧化降解反应的平均反应级数为2.49,活化能为392.73 k J/mol,反应动力学模型为rA=-dcA/dt=1.13×1047exp(-392.73/RT)c2.49A。积分法动力学分析结果表明:当反应级数n=1时,油酸甲酯热氧化降解反应的活化能为27.68 k J/mol,反应动力学模型为rA=-dcA/dt=1 690.55exp(-27.68/RT)cA,亚油酸甲酯热氧化降解反应的活化能为107.04 k J/mol,反应动力学模型为rA=-dcA/dt=2.20×1013exp(-107.04/RT)cA;当反应级数n≠1时,油酸甲酯热氧化降解反应的平均反应级数为1.45,活化能为31.29 k J/mol,反应动力学模型为rA=-dcA/dt=369.19exp(-31.29/RT)c1.45A,亚油酸甲酯热氧化降解反应的平均反应级数为1.60,活化能为108.90 k J/mol,反应动力学模型为rA=-dcA/dt=9.27×1013exp(-108.90/RT)c1.60A。积分法得到的活化能数值更为接近,因此更适合研究油酸甲酯和亚油酸甲酯的热氧化降解反应动力学。     

Inhibition of methyl linoleate autoxidation by phenolics and other related compounds under mild oxidative conditions

Methyl linoleate (MeLo) is a commercially available substrate widely used for studying the inhibitory properties of pure compounds and plant extracts against lipid oxidation. In this paper, 13 phenolic (benzoic and cinnamic acids, aldehydes and derivatives, and flavonoids) and other related compounds (butylated hydroxyanisole, butylated hydroxytoluene and tocopherols) as well as nine complex mixtures rich in phenolics (wines) or tocopherols (soybean oil extracts) were assayed for their inhibitory activity against MeLo autoxidation under mild conditions (40 °C, darkness and atmospheric pressure). Samples were also assayed for their free radical‐scavenging capacity against 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?). Protocatechuic aldehyde, a compound that has not been previously evaluated by either of the two methods, showed the highest antioxidant activity. Some variations in the antioxidant ranking for some compounds were found between our results and those obtained by other authors using accelerated conditions for MeLo oxidation. Antioxidant activity of wines and soybean oil extracts was related to their richness in phenolics and tocopherols respectively. Correlation between antioxidant capacity measured by the MeLo and DPPH^? methods was found for wines but not for the other samples studied. Therefore the measure of the free radical‐scavenging capacity of a compound is not always a reliable indicator of its lipid oxidation inhibitory ability. Copyright © 2004 Society of Chemical Industry     

尿素柱层析分离共轭亚油酸甲酯异构体的研究

利用负载型尿素层析柱对共轭亚油酸甲酯异构体进行分离。考察了固定相中甲醇残留量、尿素硅胶质量比、固定相结晶温度、层析温度及洗脱剂种类对分离效果的影响。结果表明:当固定相中甲醇残留量为3%~5%,尿素硅胶质量比为1∶1,固定相结晶温度0~8℃,层析温度0℃,洗脱剂为石油醚时,经过层析分离反10,顺12共轭亚油酸甲酯的含量从样品中的33.94%提高到57.69%。     

Autoxidation of methyl linolenate and methyl linoleate: The effect of α-tocopherol

α-Tocopherol substantially affects the distribution of peroxidic compounds formed during the autoxidation of methyl linolenate and methyl linoleate. In the autoxidation of both these unsaturated fatty acid esters the proportion of monohydroperoxides with conjugated double bonds in the trans, trans configuration is reduced until at high concentrations of α-tocopherol (5%) only cis, trans isomers are formed. In the autoxidation of methyl linolenate the proportion of hydroperoxy-epidioxides is reduced and only monohydroperoxides are formed when 5% α-tocopherol is present. The results are discussed in terms of recent findings concerning the mechanism of the autoxidation of unsaturated lipids.     

亚油酸甲酯烯烃复分解制备长链终端烯烃化合物

对亚油酸甲酯通过烯烃交叉复分解反应制备长链终端烯烃化合物1-庚烯和9-癸烯酸甲酯进行反应路线探究和工艺优化。通过对比10种底物分别与油酸甲酯和亚油酸甲酯的反应,以及以亚油酸甲酯为原料4种典型的商业烯烃复分解反应催化剂催化效果的对比,确定了反应底物和催化剂。采用单因素实验探究了反应温度、反应时间、催化剂用量和底物比对亚油酸甲酯烯烃复分解反应的影响,并通过正交实验对工艺条件进行了优化。结果表明：丁香酚是最佳的反应底物,原料转化率均达到95%以上;在4种典型的商业烯烃复分解反应催化剂中,第二代Grubbs催化剂能高效稳定地催化反应;亚油酸甲酯烯烃复分解制备长链终端烯烃化合物的最佳工艺条件为反应温度0 ℃、反应时间60 min、催化剂用量3%（以原料物质的量计）、底物比1∶ 20（原料与底物物质的量比）,在此条件下亚油酸甲酯转化率、1-庚烯产率和9-癸烯酸甲酯产率分别为99%、74%和43%。     

Impact of surfactant type, pH and antioxidants on the oxidation of methyl linoleate in micellar solutions

The oxidation of methyl linoleate micelles has been studied, aiming at elucidating the effect of various variables, including surfactant type, pH and antioxidants. The progress of the methyl linoleate oxidation was evaluated by measurement of conjugated dienes hydroperoxides (CDHP) and malondialdehyde (MDA). It was shown that the oxidative stability of methyl linoleate micelles was influenced by surfactant type, with oxidative rate being greater in SDS micelles than in Tween 20 micelles. Besides, the methyl linoleate micelles at pH 6.8 had greater rates of lipid oxidation than their pH 3.0 counterparts. Moreover, the incorporation of VE and VC in the methyl linoleate micelles successfully slowed the formation of hydroperoxides and their subsequent decomposition product MDA. However, the antioxidant activities of VE and VC were related to their concentrations.     

4-Oxo-2-nonenal as a pro-oxidant during the autoxidation of methyl linoleate in bulk phase

The effect of aldehydic lipid peroxidation products on the autoxidation of methyl linoleate (MeL) was studied at 60 °C in bulk phase. Addition of 4-oxo-2-nonenal (ONE) to MeL accelerated the formation of MeL hydroperoxides. Other tested aldehydes showed no effect on the rate of MeL autoxidation. The pro-oxidative effect of ONE disappeared when pre-existing peroxides and transition metals were removed from MeL. Further addition of ferric ion to the peroxide- and metal-free MeL recovered its pro-oxidative effect. ONE reduced ferric ion to ferrous ion effectively. Furthermore, it had a chelating ability with ferrous ion. The results suggest that the pro-oxidative effect of ONE is due to its ability to reduce transition metals and to chelate the reduced form of metal ions. Thus, ONE could accelerate the metal-dependent lipid peroxidation.     

Effects of sesamol, sesamin, and sesamolin extracted from roasted sesame oil on the thermal oxidation of methyl linoleate

This study investigated the effects of lignan compounds extracted from roasted sesame oil, which were sesamol, sesamin, and sesamolin, on oxidation of methyl linoleate (ML) during heating. These compounds were added at 500 or 1000 mg/kg to ML, and α-tocopherol was used as a reference antioxidant. The ML added with lignans or α-tocopherol was heated at 180 °C for 60 min. Thermal oxidation of ML was evaluated by conjugated dienoic acid (CDA) contents, p-anisidine value (PAV), and ML retention. Contents changes of lignan compounds or α-tocopherol in ML during heating were monitored by high-performance liquid chromatography. CDA contents and PAV of samples increased and ML decreased with heating time at 180 °C. Samples added with lignan compounds showed lower CDA contents and PAV but higher ML retention than samples without lignan compounds. The antioxidant activity of sesame oil lignan compounds in ML oxidation during heating tended to be higher than that of α-tocopherol. The contents of lignan compounds in samples decreased with heating time due to their degradation, but the degradation rates were lower than that of α-tocopherol. This study suggested that sesame oil lignan compounds be used as antioxidants in oil at high temperatures for deep-fat frying due to their higher effectiveness and stability than α-tocopherol.     

Studies on changes in flour tocopherols following ageing and treatment of the flour with chlorine dioxide

The tocopherols in freshly milled flour were measured using two-dimensional chromatography. Total tocopherols were in the range 1500–1600 μg/100 ml, but only 17–18% of this was α-tocopherol. Aerobic storage for 190 days caused a reduction of all tocopherols by 62–67%. Treatment of the flour with chlorine dioxide at the usual commercial level caused a comparable reduction, averaging 58%; ?-tocopherol was rather less affected than α-tocopherol. Studies in human volunteers indicated that a daily supplement greater than 10 mg of tocopherol was needed to bring about a significant change in the level of α-tocopherol in the blood. When bread made from untreated and chlorine dioxide-treated flour was fed to groups of volunteers in a double-blind crossover trial for 50 days on each type of bread, no significant correlation could be found between blood tocopherol levels and the type of bread consumed. To examine whether a longer period of time on the diet was necessary, the blood tocopherol levels of thirteen English students who had habitually consumed bread made from treated flour were compared with those of thirteen French students, matched for age, who had for several years consumed French bread which is made from untreated flour. The analyses were carried out in Birmingham and in Paris by the same investigator. No significant differences in tocopherol levels were found. It is concluded that the consumption of bread made from flour treated with chlorine dioxide will have no significant effect upon the blood level of α-tocopherols under the dietary conditions at present prevailing in Britain.     

Suppression of the oxidation of methyl linoleate encapsulated with the extract from defatted rice bran by a compressed hot water treatment

Bran extracts prepared by a compressed hot water treatment at 120, 150, and 180 °C for 7.5 min were used in association with maltodextrin for encapsulation of methyl linoleate. Mixtures of the bran extracts at 120 and 150 °C showed a higher emulsion-stabilizing ability than that at 180 °C. The bran extracts prepared at the higher temperature provided a higher oxidative stability as shown by the longer induction period for the oxidation of the encapsulated methyl linoleate. The induction periods of the encapsulated methyl linoleate using the bran extract prepared at 250 °C for 5 min as the aqueous phase were 3–6 times longer than those of the encapsulated methyl linoleate using water.     

尿素包合法从葡萄籽油中富集高纯度亚油酸甲酯及包合物表征分析

为提升葡萄籽的使用价值,以葡萄籽油为原料,采用尿素包合法富集高纯度亚油酸甲酯。研究了脂肪酸甲酯与尿素质量比、尿素与95%乙醇质量比、包合时间和包合温度对包合效果的影响,并采用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)和扫描电子显微镜(SEM)对空白尿素结晶物和包合固形物进行表征。结果表明:制备高纯度亚油酸甲酯的最佳工艺条件为脂肪酸甲酯与尿素质量比1∶2、尿素与95%乙醇质量比1∶4、包合温度5℃、包合时间10 h,在此条件下得到的亚油酸甲酯含量为94.83%,收率为40.41%;FTIR和XRD分析表明,尿素包合反应没有新的官能团生成,且脂肪酸甲酯的包合降低了尿素的结晶度;SEM图像显示,尿素与脂肪酸甲酯形成了六棱体包合物。综上,尿素包合法为富集葡萄籽油中的高纯度亚油酸甲酯的有效方法。     

超声波对红花籽油甲酯化影响研究

以红花籽油(经GC–MS分析含亚油酸80.17%)为原料,以亚油酸甲酯转化率为考察指标。采用超声波促进红花籽油的甲酯化反应,研究了超声功率、超声时间、碱用量、温度对甲酯化率的影响,经过试验确定最佳工艺条件为:240 W,时间20 min,KOH–甲醇∶油(mL/g)7.5∶1,温度40℃,亚油酸甲酯转化率为92.29%。     

玉米油脱色条件对生育酚含量影响研究

通过对脱色温度、脱色时间、脱色白土用量3个因素进行单因素及正交实验,研究脱色条件对玉米油生育酚含量的影响。结果表明:对生育酚含量影响的因素依次为脱色时间>脱色白土用量>脱色温度,当脱色时间为20 min,脱色白土用量为2.5%,脱色温度为105℃时,生育酚损失最少,损失率为9.3%,此时脱色油的色泽为Y35R3.2,色泽达到二级油标准。     

Role of sugar–amino acid interaction products (MRPs) as antioxidants in a methyl linoleate model system

Effects of early Maillard reaction products (MRPs) as antioxidants in methyl linoleate model system, during refrigerated storage at 5 °C for 6 days, have been evaluated. MRPs were prepared by reacting glucose with five different amino acids – glycine, methionine, tryptophan, aspartic acid and lysine – using two different concentrations and time intervals (30 mM/1 h, 30 mM/2 h, 60 mM/1 h and 60 mM/2 h). The preformed MRPs were incorporated, after studying pH and optical density profile, in a model system comprised of methyl linoleate and microcrystalline cellulose. Antioxidative characteristics were evaluated by estimating the thiobarbituric acid-reactive substance value (TBARS) and peroxide value (PV) and monitoring the gas chromatographic degradation pattern of methyl linoleate immediately after heating, as well as after storage at 5 °C for 2, 4 and 6 days. Analysis of variance revealed highly significant differences among TBARS, PV and the % of methyl linoleate degradation (p < 0.01) values, both initially and during storage in glucose + lysine and glucose + glycine with respect to control. Other treatments, such as glucose + methionine and glucose + tryptophan exhibited moderately significant differences (p < 0.05). But glucose + aspartic acid was not significantly different (p > 0.05) Significant differences were observed between 60 mM/2 h and 30 mM/1 h of MRPs with glucose + lysine and glucose + glycine (p < 0.01). Out of the five combinations tried, glucose + lysine and glucose + glycine exhibited good antioxidative potential at 60 mM/2 h. The % of antioxidant activity was in the order 60 mM/2 h > 60 mM/1 h > 30 mM/2 h > 30 mM/1 h for the treatments glucose + lysine > glucose + glycine > glucose + tryptophan > glucose + methionine > glucose + aspartic acid, respectively.     

Flowering catch crops used as forage plants for dairy cows: influence on fatty acids and tocopherols in milk

The effect of several flowering dicotyledonous catch crop plants (dicots) on milk fat quality in cows was investigated to test the hypothesis that their phenolic compounds may inhibit ruminal biohydrogenation and thus enhance the transfer to milk of intact, plant-derived polyunsaturated fatty acids. Berseem clover (Trifolium alexandrinum), buckwheat (Fagopyrum esculentum), and phacelia (Phacelia tanacetifolia) were sown in mixture with ryegrass (Lolium multiflorum; intended biomass proportion of 0.2) on 1 ha. For comparison, nonflowering chicory (Cichorium intybus, also sown in mixture with ryegrass) and pure ryegrass were cultivated. Realized biomass proportions (wet weight) were 91% for berseem clover, 69% for buckwheat, 54% for phacelia, and 51% for chicory. At the start of flowering (or from d 47 after sowing onward), cultures were harvested daily and fed for 20 d ad libitum to groups of 6 midlactation cows each. Additionally, 1 kg each of energy and protein concentrate and pure ryegrass hay were fed. Individual intake and milk yield of the cows were measured daily. Milk samples were obtained twice daily 5 d before and from 11 to 20 d after the start of treatment feeding. Feed samples were drawn twice a week from the fresh feeds. Apart from standard traits, feeds and milk were analyzed for fatty acids, tocopherols, and phenolic fractions. Only a few substantial treatment effects on intake and performance were observed. All diets based on dicots increased α-linolenic acid (ALA) concentrations in milk fat compared with the ryegrass diet even though the corresponding swards were not generally richer in ALA. The highest ALA concentration in milk fat (1.3 g/100 g of fatty acids) occurred with the berseem clover diet. Transfer rate of ALA from feed to milk was highest with the buckwheat diet (0.09) and lowest with ryegrass (0.05). This was congruent with the differences in total extractable phenols, being high in the buckwheat sward (2.6% of dry matter) and low in the ryegrass sward (1.2% of dry matter). Intermediates of ALA biohydrogenation were lowest in the milk fat of the buckwheat group, indicating an inhibitory effect of this treatment, which provided the highest dietary levels of phenols. The α-tocopherol concentration in milk was higher with the buckwheat diet than with berseem clover and phacelia diets. The study provides evidence that the ALA concentration in milk fat could be enhanced by feeding flowering dicots; however, this was due to different modes of action.