Natural polyphenols as chain‐breaking antioxidants during methyl linoleate peroxidation

A technique based on monitoring oxygen consumption was applied to study 11 natural and model polyphenols (PP, QH₂) as well as four typical monophenolics as a chain‐breaking antioxidant during the controlled chain oxidation of methyl linoleate (ML) in bulk at 37°C. The antioxidant activities of QH₂ were characterized by two parameters: the rate constant k₁ for reaction of QH₂ with the peroxy radical ${\rm LO}_{2}^{{\bf .}} $ : (i) QH₂ + ${\rm LO}_{2}^{{\bf .}} $ → ${\rm QH}^{{\bf .}} $ + LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH₂. The rate constant k₁ were reduced significantly by factor of 4 –28 as compared to these determined during the oxidation of styrene in bulk; the effect was typically more pronounced for catechol derivatives than for pyrogallol derivatives. At the same time, f for QH₂ was found to be close to two independent of the number of active OH groups, similar to that determined earlier during the inhibited oxidation of styrene. The formation of H bond between OH group of QH₂ and carboxyl group of ML is suggested as a reason for reducing effect of ML on k₁. Practical applications : This work reports rate constants for the reaction of lipid peroxyl radical with phenolics and stoichiometric coefficient of inhibition, which characterize the antioxidant activity (AOA) of 15 natural and model PP, QH₂ during the controlled peroxidation of ML. The reactivity of PP, QH₂ during the oxidation of ML is routinely lower than the reactivity during the oxidation of non‐polar model hydrocarbons. This information may be useful to estimate the AOA of natural PP, QH₂ in real systems of practical significance including plant oils, fats, food‐stuffs, biological objects, and similar.     

复合催化剂在油酸豆甾醇酯合成中的应用

以油酸和豆甾醇为原料,研究了以硫酸氢钾-金属氧化物为组合的复合催化剂在酯化合成中的应用。首先,通过与其他硫酸盐的酯化效果进行比较,筛选出KHSO4是适用于酯化合成中高效且安全的催化剂,并将其和不同的金属氧化物进行组合作为复合催化剂进一步探究酯化效果。通过实验结果比较,得到KHSO4-Zn O作催化剂的酯化率最高。然后,将KHSO4-Zn O作为复合催化剂,针对催化剂用量、反应温度、反应时间、酸醇摩尔比等因素进行考察,探究油酸和豆甾醇的最佳酯化条件。得到最佳工艺条件为:在通高纯氮气条件下,选用3.0%KHSO4+1.0%Zn O(以豆甾醇的质量分数计)为催化剂,油酸和豆甾醇的摩尔比为1.8:1,反应的温度为150℃,反应的时间为7 h,酯化率达到92.17%。本工艺利用KHSO4-Zn O作为复合催化剂,得到较高的酯化率,实现了一条合成油酸豆甾醇酯的新工艺路线。     

Preparation of fatty 3,5-disubstituted isoxazole compounds from FA esters

Long-chain fatty compounds containing an isoxazole heterocyclic ring system substituted at the 3- and 5-ring positions were prepared in moderate to good yields (40–64%) in one pot by condensing FA esters such as methyl palmitate, stearate, oleate, or linoleate with the lithiated anion of N-(isopropylidene)isopropylamine followed by dehydrative cyclization. This approach allows readily available FA esters to be utilized and incorporated into the construction of the isoxazole ring system. These novel products were isolated then characterized by NMR, IR spectroscopy, GC-MS, and m.p. Mass spectra of the fatty isoxazole compounds, derived utilizing EI ionization, showed distinctive cleavage patterns that occurred uniformly along the fatty alkyl chain allowing the position of double bonds to be readily located. Two prominent ions at m/z 97 and 110 were common to all the fatty isoxazole compounds examined and were presumably from a McLafferty rearrangement and a cyclization displacement reaction, respectively.     

6-O glucose linoleate supports in vitro human hair growth and lipid synthesis

The hair follicle is a very active organ with a complex structure, which produces a hair fibre at a rate of 0.3 mm a day. Accordingly, the hair follicle is highly demanding in energy source, as the hair bulb matrix cells are endowed with one of the highest rates of proliferation in the human body. Moreover, recent data have shown the involvement of lipids in hair follicle function. As in vitro-grown hair follicle keeps producing a hair fibre that closely resembles the natural hair fibre, we decided to use this model to investigate the role of a new of glucose linoleate derivative (6-O-linoleyl-d-glucose: 6-O-GL) as a lipid precursor and energy provider. Our results demonstrated that 6-O-GL was (i) quite stable and surprisingly resistant to oxidative degradation, and (ii) readily taken up and metabolized by the hair follicle into various lipids, namely neutral lipids, ceramides and polar lipids. Moreover, it supported hair follicle growth and survival in a glucose- and linoleic-acid free medium. 6-O-GL thus appeared to be a bi-functional nutrient, ensuring both proper fibre quality and production by the hair follicle.     

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。     

New manganese-based catalyst systems for alkyd paint drying

The autoxidation and oligomerisation of ethyl linoleate (EL) catalyzed by manganese salts in combination with several Schiff-base ligands has been studied making use of time-resolved FT-IR spectroscopy. The results indicate that several of the combinations exhibit relatively high catalytic activity for the autoxidation of EL. One of the catalyst systems was studied in more detail. The reaction between MnCl₂·2H₂O and the Schiff-base ligand (L4) formed by the condensation of 2-pyridinealdehyde and 2-aminopyridine has been studied to clarify the catalytic reaction process. It was found that the Schiff-base ligand L4 reacts with water and the tridentate ligand (2-pyridyl)(2-pyridylamino)methanol (HOL4) is formed. A single crystal structure of [Mn^III(OL4)₂]Cl·3H₂O has been determined by X-ray diffraction methods.     

Antioxidative potential of cashew phenolics in food and biological model systems as affected by roasting

The effect of different roasting conditions on antioxidant capacity of phenolics of cashew nuts and their testa was evaluated using several food and biological model systems. Total phenolic content (TPC) of cashew extracts was determined and accelerated oxidative stability of stripped corn oil in the presence of cashew extracts evaluated. In addition, the antioxidant activity of the extracts was assessed in a β-carotene-linoleate and a cooked comminuted pork model system. Inhibition of oxidation of human low density lipoprotein (LDL) cholesterol and stand breaking of supercoiled deoxyribonucleic acid (DNA) was also investigated. The TPC ranged from 5 to 791 mg gallic acid equivalents/g crude extract. In general, whole cashew nuts and testa extracts demonstrated stronger antioxidant activity than that of the cashew kernel. The inhibition percentage of LDL cholesterol oxidation, as evaluated by conjugated dines formation, of cashew kernels was higher than that of testa and was 69% at the end of 24 h incubation. Extracts of roasted cashew nut showed considerable antioxidative efficiency in model systems employed in this study, however, the effect was not significantly (P ? 0.05) different from that of their raw counterparts, except for the accelerated oxidative stability assay. The results suggest that whole cashew nut and testa extracts could be used as a potential source of natural antioxidants in certain food applications and for disease risk reduction.     

Evaluation of antioxidant property of extract and fractions obtained from a red alga, Polysiphonia urceolata

Antioxidant activity (AA), total phenolic content, and reducing power of the crude extract, fractions, and subfractions derived from a red alga, Polysiphonia urceolata, were evaluated and determined. The antioxidative activity was measured using the α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging assay and the β-carotene–linoleate assay systems, and compared with that of butylated hydroxytoluene (BHT), gallic acid (GA), and ascorbic acid (AscA). The results showed that the crude extract and the ethyl acetate-soluble fraction exhibited higher AA than BHT in the DPPH assay model, at all of four concentration levels tested (from 0.4 to 50 μg/ml), while, in the β-carotene–linoleate assay system, the crude extract and the ethyl acetate-soluble fraction exhibited similar or, in most cases, higher AA than GA and AscA at the same concentrations (from 10 to 200 μg/ml). The ethyl acetate-soluble fraction was further fractionated into seven subfractions F1–F7 by silica gel vacuum liquid chromatography. F1 was found to be the most effective subfraction in both assay systems. The total phenolic content and reducing power were determined using the Folin–Ciocalteu and the potassium ferricyanide reduction methods, respectively. Statistical analysis indicated a significant association between the antioxidant potency and total phenolic content as well as between the antioxidant potency and reducing power.     

Extraction of Lignan Compounds from Roasted Sesame Oil and their Effects on the Autoxidation of Methyl Linoleate

ABSTRACT:  Lignan compounds were extracted from roasted sesame oil and their effects on the autoxidation of methyl linoleate (ML) were studied. Lignan compounds extracted from roasted sesame oil, sesamol, sesamin, and sesamolin, were added to ML, which was then oxidized at 60 ^oC for 18 h in the dark. Alpha-tocopherol was separately added to ML for a reference antioxidant. Degree of ML oxidation was monitored by conjugated dienoic acid (CDA) contents and p -anisidine value (PAV) by AOCS methods, and ML retention by gas chromatography. CDA contents and PAV of samples increased with the oxidation time at 60 ^oC in the dark, and ML decreased. Sesamol-, sesamin-, or sesamolin-added samples showed lower CDA contents, PAV, and ML loss than the samples without lignans during oxidation in the dark, which indicated that lignan compounds lowered the ML autoxidation. The antioxidant activity of sesamol was significantly higher ( P < 0.05) than that of sesamin, sesamolin, or α-tocopherol. Lignan compounds added to ML were degraded during the autoxidation of ML, and the degradation rate was higher in sesamol- than in sesamin-, or sesamolin-added ML, but was lower than in tocopherol-added samples. As the lignan compounds concentration in ML increased, the degradation rate of lignans decreased, and the inhibition of the ML autoxidation by lignan compounds increased. The results strongly suggested that the autoxidative stability of ML could be improved by the addition of sesamol, sesamin, or sesamolin extracted from the roasted sesame oil.