Origin,metabolism, and adverse health effects of cholesterol oxidation products

Cholesterol oxidation products (COP), also called oxysterols, enter the organism by intake of COP-containing foodstuff or are generated in vivo by enzymatic or non-enzymatic oxidation (peroxidation) of cholesterol. COP are transported in lymph and blood with lipoproteins (mainly fatty acyl monoesters at the 3β-position) or bound to albumin. As being substrates for acyl CoA: cholesterol acyltransferase (ACAT), lecithin:cholesterol acyltransferase (LCAT), and cholesteryl ester transfer protein (CETP), COP are esterified and exchanged between lipoproteins and are distributed in the whole organism. Kupffer cells and hepatocytes are the target cells for COP transformation and excretion via bile secretion. Regarding biological activities, COP reveal widespread effects on cholesterol metabolism as well as on structure and function of cellular membranes. Throughout their actions, COP were shown to be cytotoxic but they were also suggested to be regulatory agents. Their detrimental part in atherogenesis seems to be still underestimated, while valid data on the role of COP in carcinogenesis are still missing.     

Effect of synthetic antioxidants on cholesterol stability during the thermal-induced oxidation of a polyunsaturated vegetable oil

As a molecule with an unsaturated bond, cholesterol is prone to oxidation. Cholesterol oxidation products (COP) are found in many common foods and have been shown to be atherogenic, cytotoxic, mutagenic, and possibly carcinogenic. Efforts to reduce the formation of oxidation products are considered important during the manufacture and processing of foods. The effect of synthetic antioxidants on cholesterol oxidation has not been extensively studied. We assayed the effect of five commonly used antioxidants—BHT, BHA, the n-propyl ester of 3,4,5-trihydroxy benzoic acid (PG), TBHQ, and 6-ethoxy-1,2-dihydro-2,4-trimethylquinoline (EQ)—on cholesterol stability when oxidation is induced in a Rancimat 679 instrument by bubbling air through the sample at 150°C. The sample consisted of 200 mg cholesterol dispersed in 100 g of a polyunsaturated vegetable oil (soybean oil). Formation of six COP was measured at the induction period, and at the 50 and 100 μS conductivity values. Under the experimental conditions, BHT and TBHQ were the most effective inhibitors of cholesterol oxidation. BHA and EQ were less effective, and PG was unable to prevent cholesterol oxidation. Synthetic antioxidants were more effective in preventing COP formation at the nucleus of the cholesterol structure than at the lateral chain.     

Linalyl acetate and methyl silicone effects on cholesterol and triglyceride oxidation in heated lard

The effectiveness of linalyl acetate (LA) at 0.02 and 0.04% as a high-temperature antioxidant was tested in lard with two levels (2 times and 10 times) of added cholesterol. Lard samples with and without added LA or methyl silicone (MS, 0.2 and 1.0 ppm) and a control with no additives were heated at 180°C for 10 hr/day for up to 240 hr. The loss of cholesterol, the formation of cholesterol oxidation products (COP) and the percentage fatty acid retention were measured during the heating periods. Addition of 1.0 ppm MS was significantly effective in reducing the loss of fatty acids (p<0.0005) in lard with 2 times the added cholesterol, but MS at 0.2 ppm was not effective in lard with 10 times the added cholesterol. Addition of LA at 0.02 and 0.04% had little effect at reducing changes in cholesterol loss, COP formation and fatty acid loss in lard samples with both cholesterol levels. But there was a tendency for MS and 0.04% LA to reduce formation of some COP in lard containing 2 times the added cholesterol and to reduce the loss of cholesterol. Presented in part at the 80th AOCS Annual Meeting, Cincinnati, OH, in May, 1989.     

Oxidative Stability of Conjugated Linoleic Acid Rich Soy Oil

This study was conducted to determine the oxidative stability of conjugated linoleic acid rich soy oil (CLARSO) and the effects of conjugated linoleic acid (CLA) levels on volatile oxidation products formed during CLARSO oxidation. CLARSO oxidative stability was determined by gravimetric analysis, peroxide value, headspace oxygen analysis and p-anisidine value. Volatile oxidation compounds were analyzed by solid phase microextraction–gas chromatography with a flame ionization detector and a mass spectrometer. CLA oxidation results were highly dependent on analytical methods used and oxidation parameters measured. The gravimetric study showed a CLA concentration effect on oxidation, which was not seen in the headspace oxygen depletion and peroxide value. Volatile oxidation data indicate that CLARSO had significantly higher (p < 0.05) levels of pentanal and trans-2-heptenal than the other oils, but there was no significant difference between the amounts of any volatiles present in 8 and 15% CLARSO. This suggests that oxidation was greater in CLARSO and that CLA concentration did not affect oxidation.     

几种低阶煤的过氧化氢氧化解聚性能研究

在40℃利用5％H2 O2水溶液分别对神府次烟煤（ SF）、准东次烟煤（ ZD）、胜利褐煤（ SL）和先锋褐煤（ XF）四种低阶煤进行了氧解,计算其氧解转化率和CO2生成率,结合元素分析、红外光谱以及酸性官能团测定结果比较了四种低阶煤的氧解性能以及其结构特征对氧化解聚性能的影响。结果表明,煤的氧化解聚与变质程度密切相关,变质程度越高,氧化反应性降低。另外煤的氧含量越高,特别是羧基以及酚羟基含量较高时,氧化解聚程度增大。     

Cholesterol Oxidation is Increased and PUFA Decreased by Frozen Storage and Grilling of Atlantic Hake Fillets (<Emphasis Type="Italic">Merluccius hubbsi</Emphasis>)

Fresh fillets of Atlantic hake were stored at −18 °C for 120 days and changes in lipid composition and the formation of cholesterol oxidation products (COP) during storage and subsequent grilling were evaluated. Fresh hake showed low COP levels (8.0 μg/g, dry basis); however, a significant increase in COP (P < 0.02) and a concomitant decrease in the cholesterol and polyunsaturated fatty acids content during frozen storage and after grilling were observed. The main cholesterol oxides present in the analyzed samples were: 19-Hydroxycholesterol, 24(S)-hydroxycholesterol, 22(S)-hydroxycholesterol, 25-hydroxycholesterol, 25(R)-hydroxycholesterol and 7-Ketocholesterol. The oxides which were more influenced by the thermal treatment were 24(S)-OH and 25(R)-OH; however, after 120 days of storage 7-ketocholesterol was the main product formed. Frozen storage and subsequent grilling under domestic conditions are important factors in damage of cholesterol and unsaturated fatty acids levels, with consequent production of cholesterol oxides, although the mechanism of the formation of these compounds by the different processes is probably different. An erratum to this article can be found at     

Effects of frying and storage on cholesterol oxidation in minced meat products

The presence of cholesterol oxidation products (COP) in the diet is a health concern for their various known adverse effects. It is important that the generation of COP be assessed during different stages of production, handling, and storage of meats and meat products so that relevant measures can be taken to minimize the production of COP. In a preliminary study, we investigated the content of COP in the lipids of raw meatballs (50% prok+50% beef), prefried meatballs (50% pork +50% beef), raw hamburger (100% beef), and prefried burger (50% pork+50% beef). Six of the common COP, viz 7α- and 7β-hydroxycholesterol, 7-ketocholesterol, 5α,6α-epoxycholestanol, 5β,6β-epoxycholestanol, and cholestanetriol, were analyzed by gas chromatography (GC) and GC-mass spectroscopy. The total content of these COP was in the range of 7 to 10 μg/g lipids in raw meatballs, prefried meat balls, and raw hamburger, after frying these samples for consumption. The prefried hamburger had ca. 8μg/g lipids of the total COP before frying, and this amount increased to 29 μg/g lipids after frying. During the storage of this fried sample, the total COP increased to 42 and 50 μg/g lipids, after 1 and 2 wk of storage, respectively. The results of this study show that freshly prepared meat products are a minor source of COP in the diet. However, if semiprepared frozen meat products are fried once and then stored for future consumption, the levels of COP can increase considerably, and this may be of concern for certain groups of consumers. Presented in part as a poster at the 88th AOCS Annual Meeting and Exposeattle, WA, May 11–14, 1997.     

PARTITIONING BEHAVIOR OF PORPHYRIN DYES IN AQUEOUS BIPHASIC SYSTEMS

ABSTRACT

The partition of protoporphyrin IX and the phthallocyanine dye, propyl astra blue iodide, in aqueous biphasic systems (ABS) and onto aqueous biphasic extraction chromatographic (ABEC?) resins has been examined. Solubility of protoporphyrin IX was found to be too low for recovery by ABS other than by use of thermoseparating surfactants. Partitioning behavior of the phthallocyanine dye was found to depend on the salting-out strength of the salt. As a result of the partition of this dye to the interface of ABS, the adoption of ABEC for recovery of this dye is more favorable.     

Experimental investigation and simulation of gas-liquid-liquid reactive extraction process for the production of hydrogen peroxide

The gas-liquid-liquid reactive extraction system for the production of hydrogen peroxide via anthraquinone route was investigated. The oxidation of the hydrogenated anthraquinone working solution by oxygen and the extraction of hydrogen peroxide from the working solution with deionized water were carried out simultaneously in a sieve plate column of 50 mm in diameter. The effects of the superficial velocity of oxygen on the conversion of 2-ethylanthrahydroquinone and the extraction efficiency of hydrogen peroxide were investigated, separately. The results showed that the oxidation and the extraction do not hamper each other, on the contrary, the presence of gas in the column can promote the transfer of hydrogen peroxide from the organic phase to the aqueous phase, therefore, the conversion of 2-ethylanthrahydroquinone and the extraction efficiency of hydrogen peroxide increased with the increase of gas superficial velocity. In addition, a mathematical model for the simulation of the gas-liquid-liquid reactive extraction process was developed. The predicted values were compared with the experimental data at different conditions and the agreement was found to be quite satisfactory for the production of hydrogen peroxide in a sieve plate column.     

Effects of Deuterium Oxide on the Oxidative Stability and Change of Headspace Volatiles of Corn Oil

Effects of deuterium oxide and deuterium oxide-free water on the oxidative stability and formation of headspace volatiles were determined for corn oils to evaluate the role of moisture as an active influential factors during lipid oxidation. Mixtures of corn oil and water with different ratios of deuterium oxide were prepared, and the mixtures were stored at 60 °C for 2 days. Headspace oxygen contents, conjugated dienoic acid (CDA) values, and p-anisidine values (p-AV) were analyzed as a measure of oxidative stability, and headspace volatiles were analyzed by solid phase microextraction and a gas chromatography mass selective detector to determine the involvement of deuterium in volatiles. Deuterium oxide accelerated the rate of lipid oxidation in corn oil compared to oils with deuterium-free water based on the results of headspace oxygen content, CDA, p-AV, and total volatile content. Fragmented mass to charge ratios (m/z) of 73.1/72.1 for d ₁-pentane/pentane and 57.0/56.0 for d ₁-2-propenal/2-propenal from samples containing deuterium oxide were significantly higher than those from deuterium oxide-free water, implying that moisture participated to form volatiles in corn oil oxidation under air-tight condition. Deuterium oxide appeared to accelerate the rate of lipid oxidation in corn oils and participated to form volatiles from oils during oxidation.     

苯胺在超临界水中氧化反应路径

An aqueous solution of aniline was oxidized in supercritical water with a flow reactor under the conditions of 25 MPa, 300％ excess oxygen, 2.351×10-4 mol*L-1 aniline .GC-MS analysis of the oxidation products extracted from the aqueous reactor effluent permitted identification of compounds such as azobenzene, phenazine and acetic acid. The products could be classified as dimers,single-ring or ring-opening produces,carboxylic acids and ultimate products.The contents of dimers (such as azobenzene and phenazine) were greater than other products.A reaction network consistent with the experimental observations was developed. The study revealed that aniline might be oxidized to ultimate products through two parallel pathways. The formation of dimers such as azobenzene, phenazine and the further oxidation of these dimers were the main pathways. It was indicated experimentally that the rate controlling step of aniline oxidation was the further oxidation of azobenzene and phenazine, but not the further oxidation of organic acid such as acetic acid, formic acid and so on.     

Hydroperoxide as a Prooxidant in the Oxidative Stability of Soybean Oil

Fifteen milliliters of soybean oil having peroxide value (PV) of 0, 2, 4, 6, 8, or 10 meq/kg oil in a 35 mL serum bottle was sealed air-tight with a Teflon rubber septum and aluminum cap and was stored in a forced-air oven at 50 °C. The oxidative stability of soybean oil was evaluated daily for six days by measuring the headspace oxygen content and volatile compounds in the headspace of a sample bottle by gas chromatography. As the initial PV of the oil increased from 0 to 2, 4, 6, 8 and 10, the headspace oxygen decreased and the volatile compounds increased at p < 0.05. Hydroperoxide accelerated the oxidation of soybean oil. The correlation coefficient (R ²) between the headspace oxygen and the volatile compounds was 0.95. The increase of tertiary butyl hydroquinone (TBHQ) from 0 to 50 ppm for the oil of PV 4 or 8 had a significant effect on the oxidative stability at p < 0.05. The increase from 50 to 100 ppm for the oil of PV 4 or 8 did not significantly increase the stability at p > 0.05. The oxidative stability of PV 8 meq/kg and 50 ppm TBHQ was better than the control with PV 0 and 0 ppm TBHQ at p < 0.05. TBHQ was an effective antioxidant to improve the oxidative stability of soybean oil.     

Lipid oxidation in potato chips

Qualitative and quantitative analyses of volatile compounds in fresh and aged potato chips and unused fresh and aged frying oils showed that oxidation of oils was mainly responsible for volatile compound changes in potato chips during storage. The lipid oxidation of potato chips was determined by measuring the peroxide value of potato chips and the amount of volatile compounds and oxygen content in the headspace of potato chip bottles by gas chromatography. The correlation coefficients between volatile compounds and oxygen content, volatile compounds and peroxide value, and peroxide values and oxygen content were -0.93, 0.95 and -0.93, respectively. These high correlation coefficients indicated that volatile compound changes in potato chips during storage were mainly due to the oxidation of oil. The lipid oxidation of potato chips during storage can be studied by measuring oxygen content and the amount of volatile flavor compounds in the headspace. The potato chips produced in oil containing an antioxidant tertiarybutyl hydroquinone (TBHQ) had better oxidation stability than the chips fried in oil without TBHQ.     

S-nitrosocysteine (RSNO), an effective antioxidant in cured meat

S-nitrosocysteine (RSNO), a compound which has been shown to be generated during the curing process of meat, was found to act as an antioxidant. The antioxidative activity of RSNO in an aqueous linoleate model system, in the presence of myoglobin, was compared with that of other known antioxidants, such as BHT and α-tocopherol. The results indicated that RSNO has an antioxidative activity only slightly lower than that of BHT. During the initial stage of the reaction, RSNO acted not only as an inhibitor of linoleic acid oxidation, but also as a hydroperoxide decomposer. The high inhibitory effect of added RSNO (1mM/kg meat) on lipid oxidation in ground cooked turkey meat was demonstrated in the product itself.     

DSC determination of thermally oxidized olive oil

The feasibility of using DSC as an analytical method to evaluate the autoxidation of olive oil at 50°C and thermal oxidation at 93 and 180°C in 10-mL airtight vials was studied. DSC peak enthalpy and peak crystallization temperatures were compared with headspace oxygen depletion and headspace volatiles in oxidized oil samples. A single crystallization peak was found in olive oil. The crystallization peak shifted to lower temperatures, and the enthalpy associated with this phase transition decreased as the exposure time increased at 93 and 180°C. DSC peak enthalpy in olive oil at 50, 93, and 180°C showed correlations of 0.84, 0.91, and 0.95, respectively, with headspace oxygen depletion in sample bottles. Correlation of DSC initial peak temperature with headspace oxygen depletion was 0.53, 0.87, and 0.95 at 50, 93, and 180°C, respectively. Correlations of DSC peak enthalpy and initial peak temperature with headspace volatiles at 180°C were 0.95 and 0.97, respectively. These results indicate that DSC is a good analytical method to determine the oxidative stability of olive oil at frying temperature.     

Industrial trial to evaluate the effect of oxygen concentration on overall quality of refined, bleached, and deodorized soybean oil in PET bottles

Soybean oil, owing to its FA composition, is highly susceptible to deterioration by oxidation. The use of nitrogen gas permits the removal of dissolved oxygen and oxygen in the headspace of tanks and bottles. The objective of this work (an industrial trial) was to evaluate the shelf life of soybean oil packaged in polyethylene terephthalate (PET) bottles with different levels of oxygen in the headspace (<0.3, 5–6.5, 7–9, and >15%). The quality of the oil was evaluated during 6 mon. FFA and moisture increased and the smoke point decreased in all experimental conditions, even though the difference between the experiments was not significant. An increase was observed for peroxide value (PV), anisidine value (AV), and specific extinction, and higher increases in these parameters were observed in higher oxygen concentrations. After 180 d, the difference between the PV and AV was significant. According to sensory analysis, the shelf life of the oil increased from 60 to 90, 120, and 180 d as the initial concentration of oxygen was reduced from >15%, 7–9%, 5–6.5%, and 0–3%, respectively. The results demonstrated that shelf life of soybean oil packaged in PET bottles can be significantly increased by using nitrogen to reduce available oxygen in the headspace.     

氧气在醋酸水溶液中的Henry系数计算模型

高温下氧气在醋酸水溶液中的Henry系数目前还没有合适的计算方法。胡英等(1985)提出的扩展定标粒子理论虽然可在广泛的温度范围内适用于多种体系,但目前还没有将这一模型应用于有机酸溶液的报道。文中对扩展定标粒子理论进行了二点改进,一是考虑了热力学参数对温度的依赖关系;二是针对有机酸溶液的特点对氧气的有效大小参数进行了调整,建立了氧气在醋酸水溶液中的Henry系数计算模型。模型参数由文献实验数据回归得到,模型计算结果与文献报道值基本一致,所建立的模型可用于关联和预测不同温度(273—500 K)、不同醋酸摩尔分数(0—100%)下氧气在醋酸水溶液中的Henry系数。     

Effect of α-, β-, γ-, and δ-Tocotrienol on the Singlet Oxygen Oxidation of Lard

The impacts of four different types of tocotrienol homologues on the singlet oxygen oxidation of lard were evaluated by measuring the headspace oxygen content and the peroxide value. Singlet oxygen oxidation of lard was induced by chlorophyll photosensitization. Samples of 0.100, 0.250, and 0.400 M lard in methylene chloride containing chlorophyll and α‐, β‐, γ‐, or δ‐tocotrienol were prepared and stored under light at 3,000 lux for 4 h. All tocotrienol homologues at 1.20 mM significantly prevented the singlet oxygen oxidation of lard. Chlorophyll under light produced singlet oxygen at 1.09 μmol oxygen/mL headspace/h. A steady state kinetic study showed that tocotrienols reduced the singlet oxygen oxidation of lard by quenching the singlet oxygen. Singlet oxygen reacted with lard at 6.50 × 10⁴M^?1 s^?1. α‐, β‐, γ‐, and δ‐tocotrienol quenched singlet oxygen with the rate of 2.16, 1.99, 2.05, and 0.800 × 10⁷M^?1 s^?1, respectively. Among them, α‐tocotrienol significantly prevented singlet oxygen oxidation of lard.     

Metal-catalyzed oxidation in the presence of water in foods

Methyl linoleate was oxidized in model systems consisting of either cellulose or casein with which the lipid was dispersed with water containing cobalt salts. The dispersion was extruded into Warburg flasks, frozen and freeze-dried at 100 μ Hg and with platen temperatures of 80 F. The samples were then humidified over saturated salt solutions to give moisture contents from less than 1 g H₂O/100 g solids up to 30 g H₂O/100 g solids. The higher moisture contents were obtained by addition of glycerol to the model system during preparation and humidification at 60–75% RH. Chelating agents including EDTA and citric acid in concentrations of 1 to 10 moles per mole of cobalt ion were used in some experiments. Oxidation was followed manometrically and by peroxide analysis. At low water contents, water acts as an antioxidant through hydration of metallic catalysts. As the moisture content increases, water promotes oxidation through its solvent activity. In the region of capillary condensation, antioxidant effect of metal hydration is overshadowed by the prooxidant effect of metal solubilization. The water soluble chelating agents such as EDTA act on metals in aqueous solution and their activity is promoted by increased moisture content. One of 28 papers presented at the Symposium, “Metal-Catalyzed Lipid Oxidation,” ISF-AOCS World Congress, Chicago, September 1970.