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.     

Chemical Characterization and Physical Properties of Solvents Derived from Epoxidized Methyl Soyate

Reactions of epoxidized methyl soyate (EMS) with alcohols, carbon dioxide, and acetone yielded liquids with solvent properties that make them more suitable than methyl soyate for dissolving polar substances. The reactions of EMS in the presence of Amberlyst‐15 with alcohols, including methanol, ethanol, n‐butanol, and 2‐methoxyethanol, produced a series of solvents containing ether (–OR) and alcohol (–OH) groups. Reactions of EMS with carbon dioxide and acetone gave products with carbonate and ketonide functional groups, respectively. The complex mixture of compounds present in the product, EMS(MeOH), resulting from the reaction of EMS with MeOH, was characterized by MS and NMR investigations. In addition to products resulting from MeOH addition across the epoxide ring, were major amounts of cyclic tetrahydrofuran derivatives that were derived from reactions of methyl linoleate (18:2) with MeOH. All of the solvents were characterized by high boiling points and low vapor pressures. Their viscosities were higher than that of methyl soyate. Especially notable were their very high Kauri‐butanol values, which ranged from 280 to 852, all of which are much higher than that (57) of methyl soyate. Such high KB values indicate that these solvents have very favorable solubilizing properties, which is illustrated by the ability of EMS(MeOH) to readily dissolve both polar (e.g., MeOH) and non‐polar (e.g., hexane) compounds.     

A study of new manganese complexes as potential driers for alkyd paints

In the search for new autoxidation catalysts, the oxidative crosslinking of ethyl linoleate (EL) has been monitored using time-resolved FT-IR (Fourier transform IR spectroscopy), size-exclusion chromatography and GC/MS (gas chromotography/mass spectroscopy). These methods seem to be quite sensitive to changes in the structure of the catalyst. It has been found that the compound [Mn(acac)₃] (Hacac = 2,4-pentanedione) is an efficient catalyst for the oxidation and the oligomerization of EL, which is proposed to proceed not only via hydroperoxide decomposition, but also through substrate activation. The system [Mn(acac)₃] with added bpy (=2,2′-bipyridine) has a very high activity for the oxidation of EL. In situ formation of the species [Mn^II(acac)₂(bpy)] and [Mn^III(acac)₂(bpy)]⁺, and the high reactivities of these two species with hydroperoxides and with EL, respectively, are proposed as an explanation for the observed high oxidation rate. Presented at XXVIIIth FATIPEC Congress, organized jointly by the Hungarian Chemical Society (MKE) and the Polish Association of Chemical Engineers (SITPCHEM), in Budapest, Hungary, June 12–14, 2006.     

Phenolic contents and antioxidant activities of bitter gourd (Momordica charantia L.) leaf, stem and fruit fraction extracts in vitro

Bitter gourd (Momordica charantia L.) has long been regarded as a food and medicinal plant. We investigated the antioxidant activity of the water extract of leaf, stem and fruit fractions by several in vitro systems of assay, namely DPPH radical-scavenging activity, hydroxyl radical-scavenging activity, β-carotene–linoleate bleaching assay, ferric reducing/antioxidant power (FRAP) assay and total antioxidant capacity. Total phenolic content was measured by Folin–Ciocalteu reagent. Identification of phenolic compounds was achieved using HPLC with the UV-diode array detection. The extracts of different fractions were found to have different levels of antioxidant activity in the systems tested. The leaf extract showed the highest value of antioxidant activity, based on DPPH radical-scavenging activity and ferric reducing power, while the green fruit extract showed the highest value of antioxidant activity, based on hydroxyl radical-scavenging activity, β-carotene–linoleate bleaching assay and total antioxidant capacity. The predominant phenolic compounds were gallic acid, followed by caffeic acid and catechin. The present study demonstrated that the water extract fractions of bitter gourd have different responses with different antioxidant methods. Total phenol content was shown to provide the highest association with FRAP assay in this present study (R² = 0.948).     

Rancidity in hazelnuts due to volatile aliphatic aldehydes

Hazelnut kernels became rancid on storage under ambient conditions in the presence of air. The kernels have a high oil content. The oil contains approximately 75 g per 100 g oleic acid (18:1) and 9 g per 100 g linoleic acid (18:2). Rancidity was detected organoleptically, by gas chromatography/mass spectrometry of the volatile off-flavour compounds and by reduction in both the total fatty acid content (g per 100 g oil) and the iodine value (g per 100 g oil). There was an accumulation of volatile alkanals, 2-alkenals and alkanoic acids on storage of the kernels at ambient temperature in the presence of oxygen. Hexanal (derived from oxidation of linoleic acid) and octanal (derived from oxidation of oleic acid) increased over tenfold on storage, whilst there was concomitant decrease in fatty acid content (83 g per 100 g oil) and iodine value (79) during the same period. It is suggested that analysis of volatile aldehydes such as hexanal and octanal could be used to assess rancidity in foods or oils rather than relatively nonspecific tests such as iodine or peroxide value. There was no evidence in this work that the rancidity was due to microbial spoilage.     

嗜酸乳杆菌亚油酸异构酶在毕赤酵母中的分泌表达

以嗜酸乳杆菌AS1.1854来源的亚油酸异构酶基因为模板,用PCR方法扩增目的片段,并克隆到pMD19T载体.经双限制性酶切的pMD19T-LAI和载体pPICZαA连接转化得到重组质粒pPICZαA-LAI.将阳性重组质粒用sac Ⅰ进行线性化后,经化学法转化毕赤酵母GS115.提取重组酵母GS 115/pPICZαA - LAI基因组,利用交叉引物通过PCR方法筛选重组子.阳性毕赤酵母GS115/pPlCZαA-LAI经1％甲醇诱导,分泌表达出相对分子质量为69 000亚油酸异构酶.经测定发酵上清酶活力为0.107 U,未破碎重组酵母酶活力0.08 U.     

Improving the oxidative stability of polyunsaturated vegetable oils by blending with high-oleic sunflower oil

Mixing different proportions of high-oleic sunflower oil (HOSO) with polyunsaturated vegetable oils provides a simple method to prepare more stable edible oils with a wide range of desired fatty acid composition. Oxidative stability of soybean, canola and corn oils, blended with different proportions of HOSO to lower the respective levels of linolenate and linoleate, was evaluated at 60°C. Oxidation was determined by two methods: peroxide value and volatiles (hexanal and propanal) by static headspace capillary gas chromatography. Determination of hexanal and propanal in mixtures of vegetable oils provided a sensitive index of linoleate and linolenate oxidation, respectively. Our evaluations demonstrated that all-cis oil compositions of improved oxidative stability can be formulated by blening soybean, canola and corn oils with different proportions of HOSO. On the basis of peroxide values, a partially hydrogenated soybean oil containing 4.5% linolenate was more stable than the mixture of soybean oil and HOSO containing 4.5% linolenate. However, on the basis of volatile analysis, mixtures of soybean and HOSO containing 2.0 and 4.5% linolenate were equivalent or better in oxidative stability than the hydrogenated soybean oil. Mixtures of canola oil and HOSO containing 1 and 2% linolenate had the same or better oxidative stability than did the hydrogenated canola oil containing 1% linolenate. These studies suggest that we can obviate catalytic hydrogenation of linolenate-containing vegetable oils by blending with HOSO. Presented at the AOCS/JOCS joint meeting, Anaheim, CA, April 25–29, 1993.     

正十六烷和亚油酸甲酯-正十六烷系统凝固过程的分子动力学模拟

采用分子动力学模拟方法,研究了正十六烷体系和添加了亚油酸甲酯分子的正十六烷混合体系的凝点变化及凝固前后的微观结构变化信息。研究表明,添加亚油酸甲酯后,正十六烷系统的凝点有所下降,且下降值随添加量增加而增加。计算了不同温度下正十六烷的链头尾距。发现,随着温度的下降,链头尾距均由较为无序的分布逐渐转化以全伸展为主的较为有序的分布,这与混乱度随温度降低而降低的热力学原理相一致。添加亚油酸甲酯后,由于其链中具有两个顺式双键构象和近似块状的酯基结构,使得其周围的正十六烷分子链的结构发生微变,即仍保持一定的弯曲度,从而使混合系统在低温下仍可保持一定的流动性,凝点也相应降低。     

The effect of silylation on titanium-containing silica catalysts for the epoxidation of functionalised molecules

The epoxidation of functionalised substrates of interest as fine chemicals using mesoporous titanium-containing silicas is here reported and the role of silylation in changing the surface hydrophilic character of these catalysts is investigated. The silylation procedure was carried out on two titanium-grafted silicas with different morphologies. An ordered MCM-41 and a non-ordered commercial mesoporous silica were used as supports. The reactivity of bulky substrates with different characteristics (limonene, -terpineol, carveol and methyl linoleate) is studied and compared. The effect of silylation is more pronounced on Ti–MCM-41 than with low-surface area Ti–SiO₂ and it is shown that the catalytic performances are strongly dependent on the nature of the reactant. Purely alkenic molecules show better reactivity over silylated catalysts than over non-silylated ones. On the other hand, a hydrophilic environment around the titanium active sites has often a beneficial effect in the epoxidation of richly functionalised substrates.