胆固醇受热氧化产物研究

对胆醇醇受热氧化情况进行了研究。采用毛细管气相色谱法分离检测胆固醇氧化产物。胆固醇于90℃加热2h和高温下加热初期（150℃，10min以内），没有明显的氧化物生成。但高温加热时间较长（20min以上）时，自氧化反应很容易发生，共有6种氧化产物（5β、6β－环氧化胆固醇、5α、6α－环氧化胆固醇、3β，5α，6β－胆甾烷三醇、6－酮基胆固醇、7－酮基胆固醇、25－羟基胆固醇）被确定。胆固醇氧化产物组成和生成量与胆固醇的量、加热温度及加热时间有关。     

肉食品中的胆固醇氧化物

胆固醇是肌肉组织的一种组分。新鲜肉中不存在胆固醇氧化物。内在长期贮存和加热中生成胆固醇氧化物。肉食品中的胆固醇氧化物对人的健康有害。肉中胆固醇氧化物的总量与肉的脂类氧化物存在着线性相关。在饲料中添加生育酚以提高内源性生育酚，其动物的肉制品中胆固醇氧化物明显减少。     

胆固醇在三硬脂酸甘油酯和三油酸甘油酯中的高温氧化特性

为了阐明组成三酰甘油的脂肪酸是否饱和对胆固醇氧化的影响,使用气相色谱-质谱联用技术研究了胆固醇在三硬脂酸甘油酯(GTS)和三油酸甘油酯(GTO)中的氧化情况,并同步跟踪过氧化值的变化。结果表明:胆固醇在GTS和GTO中的主要氧化产物为7α-羟基胆固醇、7β-羟基胆固醇、5,6β-环氧基胆固醇、5,6α-环氧基胆固醇、7-酮基胆固醇。在160℃加热条件下,胆固醇氧化产物随时间先增加后减少,未氧化胆固醇逐渐减少,在GTO中过氧化值在加热1 h出现最大值(500.46 meq/kg),在GTS中过氧化值在加热3 h出现最大值(401.30 meq/kg),随后逐渐降低。在110℃加热条件下,胆固醇在GTS中不会氧化,过氧化值亦较低,加热96小时出现最大值(278.43 meq/kg),胆固醇在GTO中几乎完全氧化,过氧化值迅速增加,最大值出现在加热12 h(1486.88meq/kg),随后逐渐减少。总的来说,160℃和110℃加热条件下,胆固醇在GTS中比在GTO中稳定,过氧化值的产生亦会延迟且生成量较小,因此,饱和脂肪酸三酰甘油更有助于保持胆固醇在高温下的稳定性。     

不同媒介环境下胆固醇的高温氧化特性研究

目的:研究空气、脂肪酸(硬脂酸、油酸)、食用油(猪油、玉米油)等不同媒介环境条件下,胆固醇的高温氧化特性。方法:采用气相色谱检测胆固醇及其在高温(180℃)条件下的主要氧化产物(7α-羟基胆固醇、7β-羟基胆固醇、5,6β-环氧基胆固醇、5,6α-环氧基胆固醇、7-酮基胆固醇)。结果:胆固醇在空气中易于氧化。随着加热时间的延长,未氧化胆固醇显著减少,所生成胆固醇氧化产物缓慢增加。脂肪酸(硬脂酸、油酸)中,在加热初期(30min)胆固醇氧化速度减缓,加热末期(120min)其氧化速度增加。食用油(猪油、玉米油)中,胆固醇在加热初期(30min)氧化速度显著减缓,在加热末期(120min)油脂的减缓作用不复存在。结论:胆固醇的高温氧化特性与所处媒介环境有关。     

不同饱和度的三酰甘油酯的共存对胆固醇氧化的影响

为了评价三酰甘油酯的不同饱和程度对胆固醇氧化的影响,将精制的沙丁鱼油三酰甘油酯(碘价IV=182.6)、部分氢化沙丁鱼油三酰甘油酯(IV=174.5)、全氢化沙丁鱼油三酰甘油酯(IV=92.0)分别与胆固醇混合,制成CST、CTPH和CTFH三组试样,在25℃避光处诱导其氧化。研究结果表明:试样的氧化稳定性随着上述各试样的不饱和程度的增加而降低。CST的过氧化物诱导期比CTPH的短,并且在较短的诱导期内CST中组成沙丁鱼油三酰甘油酯的高度不饱和脂肪酸(PUFA)比CTPH的明显减少。各试样中生成的主要胆固醇氧化物有7-β-羟基胆固醇、7-酮基胆固醇、β-环氧化胆固醇和胆甾烷三醇。胆固醇氧化物的生成量随着过氧化物价(POV)的变化和PUFA的减少而增加。胆固醇的氧化与共存的鱼油三酰甘油酯的自动氧化有关。尽管在胆固醇氧化物生成阶段,降低鱼油三酰甘油酯的不饱和度可有效地延缓胆固醇的氧化,但是在诱导期以后胆固醇的氧化速率与CST和CTPH中PUFA的比例无关。     

气质联用法测定反复冻融畜禽肉中胆固醇及其氧化物含量

本文以畜禽肉中胆固醇及胆固醇氧化物、水分、丙二醛指标变化,考察了反复冻融对畜禽肉品质的影响。采用气相色谱-串联质谱/质谱(GC-MS/MS)测定方法,对反复冻融7次(新鲜肉记为冻融0次)后鸡肉、猪肉和牛肉中胆固醇及5种胆固醇氧化物(25-羟基胆固醇、7β-羟基胆固醇、20α-羟基胆固醇、5α,6α-环氧化胆固醇、7-酮基胆固醇)的含量进行了测定。结果表明,随着冻融次数的增加,胆固醇含量逐渐降低,其中牛肉中的胆固醇含量减少尤为明显(减少量为32.47 μg/g)。在反复冻融的过程中,胆固醇氧化物的含量先逐渐增加,后趋于平稳,其中鸡腿肉中7β-羟基胆固醇含量增加最多(增加量为0.601 μg/g)。同时,通过对畜禽肉中脂质过氧化过程中的水分含量和丙二醛含量进行考察,鸡胸肉中的水分减少最多(减少量为14.472 g/100 g),牛肉中的丙二醛增加量最多(增量为1.004 μg/g)。反复冻融会导致畜禽肉胆固醇氧化增加,品质下降。     

基于ESR技术检测水产品加工过程中的氧化物质

以扇贝、鲍鱼、杂色蛤、牡蛎为主要原料,采用电子自旋共振波谱(ESR)技术检测原料在加工过程中的氧化物质。以扇贝为研究对象,以POBN为捕获剂,采用2种自旋捕获方案,即:方案1,将原料匀浆,按比例加入POBN(终浓度为40 mmol/L),热处理后,ESR检测;方案2,原料热加工处理后,匀浆,按比例加入POBN(终浓度为40 mmol/L),置于37℃水浴中保温30 min,ESR检测,同时以加热时间,加热温度为变量,检测不同加工条件对脂类自由基生成的影响。在最优方案条件下,以畜禽肉(猪肉、鸡肉、牛肉)作为对照,比较鲍鱼、杂色蛤、牡蛎加工过程中的氧化物生成。研究结果表明,方案1在相同时间,自由基氧化物生成量随加热温度的升高而增多;相同温度下,自由基氧化物生成量随加热时间的增长而增多;方案2在相同时间内,自由基氧化物生成量随温度的升高和时间的延长而增加,2 h后逐渐减少。采用筛选的最优方案(方案1),3种贝类整体比畜禽肉产生的自由基氧化物多,其中牡蛎的氧化物生成最多。本研究结果对于水产品加工过程中有效控制氧化物生成提供一定的理论参考依据。     

精制鱼油三甘油酯时与之共存下的胆固醇的氧化分解

使用鳕鱼肝脏抽出的 ,经精制的鱼油三甘油酯、胆固醇和三油酸甘油酯纯品 ,分别组成 4组试样 :胆固醇与精制鱼油三甘油酯 (CFT) ;胆固醇与三油酸甘油酯 (CT) ;三油酸甘油酯 (TO) ;胆固醇 (CHOL) ,放置在 2 5℃干燥空气中贮存 ,定期对各组的氧吸收量进行测定 ,并对其中三甘油酯和胆固醇的氧化分解产物进行定性、定量分析。经 10 4d的贮存 ,只有CFT组的氧吸收量增加 ,并生成游离脂肪酸和胆固醇氧化物。而且胆固醇氧化物的数量 ,随着高度不饱和脂肪酸 (PUFA)和油酸的减少而增加。研究结果表明 ,水产制品中胆固醇的氧化与共存的油脂中的PUFA的氧化分解有关。     

氧化·疾病·抗氧化(二十五)

<正>5.4.2.3　对体内抗氧化胁迫强化作用当摄入胆固醇氧化物时,可使血清和肝脏等脂质发生氧化胁迫并产生过氧化脂质和氧化胆固醇等积聚。为此,有人用0.5%和2.5%苹果多酚(APP)加入大鼠饲料,饲料中加入0.3%胆固醇氧化物,每组7只,经饲养3周以观察APP对亚油酸自动氧化时抗氧化活性。结果APP组与对照组相比,由于胆固醇氧化物摄入,使血清     

玉米油高温加热过程中豆甾醇氧化物的检测

甾醇氧化受温度、氧化时间、基质等因素影响,甾醇在低于120℃下基本不氧化,当温度高于180℃时、加热1 h,有80%甾醇被氧化。甾醇和其氧化物在超过150℃下会发生降解反应,引起植物甾醇分子裂解,并产生挥发性化合物和低聚物。采用皂化、固相萃取对POPs进行前处理,GC-MS检测植物油中的甾醇氧化物,能够有效分离植物甾醇氧化物的异构体。对玉米油样品进行有效分析,发现玉米油在180℃及以上温度加热会产生甾醇氧化物,但甾醇氧化物的产生与分解同时动态进行,除在180℃下加热的6、8 h、复热时以及在260℃加热条件下的8 h、复热0.5 h,其他温度下均检出豆甾醇氧化物。     

Influence of Dietary Supplementation with α-Tocopheryl Acetate and Canthaxanthin on Cholesterol Oxidation in ω3 and ω6 Fatty Acid-enriched Spray-dried Eggs

ABSTRACT: The effect of feeding laying hens linseed oil or sunflower oil, with and without α-tocopheryl acetate and/or canthaxanthin, was evaluated on cholesterol oxidation in spray-dried whole egg at various storage periods. Storage of spray-dried eggs at room temperature in the dark resulted in an increase in cholesterol oxidation products from 18.1 μg/g, after spray drying, to 39.3 μg/g, at 12 mo of storage. No differences were found with either dietary oil or canthaxanthin supplementation. However, α-tocopheryl acetate supplementation resulted in a lower formation of cholesterol oxidation products during storage. No synergistic effect between α-tocopherol and canthaxanthin was detected.     

Effects of esterification on the formation and decomposition of steryl hydroperoxides

The aim of the study was to investigate the effects of esterification on the hydroperoxide formation and decomposition of steryl ester to be able to evaluate early phases of autoxidation. In order to study hydroperoxides of intact steryl esters, a novel HPLC–ELSD method was developed. Steryl ester hydroperoxides were separated using a silica column with heptane-MBTE gradient. The method was applied to study the formation and decomposition of steryl moiety hydroperoxides in cholesteryl stearate during heating at 100 °C. To investigate the effect of esterification, also the formation of hydroperoxides in free cholesterol was measured. To confirm the results obtained by HPLC and to follow the decomposition of the hydroperoxides, peroxide values and secondary oxidation products were determined. The new HPLC showed that 7α- and 7β-OOH were the predominant hydroperoxides. In purified cholesteryl stearate, their amounts were highest (47–62 mg/g) after heating for 2–3 days, and after 4 days only small amounts were found. The formation of secondary oxidation products was marked when the amount of hydroperoxides was high. Presence of impurities in the commercial steryl ester preparation increased significantly the oxidation rate. Free cholesterol oxidised more slowly than the ester. The amount of 7-OOH epimers was only 2.6 mg/g for free cholesterol after 3 days. In conclusion, the new method was shown to be a useful tool for the determination of individual intact steryl ester hydroperoxides. The esterification of sterol affected both the rate of oxidation and the amount of formed oxidation products.     

Influence of Surface Structure on Cholesterol Oxidation in Model Food Powders

Three milk-resembling powders having different oil phases were prepared and stored for six months at room temperature. Samples were taken monthly for estimation of the surface composition by ‘electron spectroscopy for chemical analysis’ (ESCA) and analyses of the level of cholesterol oxides by gas chromatography. The highest fat coverage was obtained with technical tristearin as the oil phase. This preparation had around 75% of the powder surface covered by fat; during storage this coverage decreased. This powder also had the largest increase in cholesterol oxides during storage, the final level being 159 μg g⁻¹ cholesterol. The powder containing high-melting pure tristearin had a low surface coverage of fat, originally about 25%, which decreased during the storage period. Little increase in cholesterol oxides was observed, the final level being 52 μg g⁻¹ cholesterol. The third powder containing liquid triolein as oil phase, had a surface coverage of about 50% throughout the storage period. The cholesterol oxidation rate was in between that of the two tristearin powders, the final level of oxides being 75 μg g⁻¹ cholesterol. The results for the investigated powders indicate that the surface composition is of major importance for the oxidation of cholesterol. No correlation between cholesterol oxidation and solvent extractable fat (free fat) was found.     

Stability of Cholesterol and Paprika Carotenoids in Egg Powders as Influenced by Dietary and Processing Treatments

The effects of dietary α-tocopherol and/or oleoresin paprika (OP) on cholesterol and carotenoid stability in egg powders during spray drying and subsequent storage were investigated. Cholesterol oxidation and loss of carotenoids in eggs dried with a direct gas-fired spray dryer were greater ( P< 0·05) than in eggs dried using an indirect (electric) heating system. Dietary supplementation of α-tocopherol acetate (200 mg kg⁻¹ feed) significantly increased ( P< 0·01) the oxidative stability of cholesterol and carotenoids in eggs dried with the direct heating system. Supplementation of OP (7·5 μg g⁻¹ egg lipids) through diet or by direct addition to liquid eggs did not affect the formation of cholesterol oxidation products (COPS) during storage. However, increased concentrations of OP in liquid eggs (15 and 30 μg g⁻¹ lipids) suppressed the formation of COPS during processing and subsequent storage.     

Lipid and cholesterol oxidation in chicken meat are inhibited by sage but not by garlic

The effects of the addition of sage and garlic in chicken meat on lipid and cholesterol oxidation, having as prooxidant factors the addition of salt, thermal treatment, and frozen storage, were evaluated. The content of unsaturated fatty acids did not change in the presence of sage; on the contrary, with garlic, the content of these fatty acids decreased after cooking and storage. Hexanal and pentanal contents were lower in patties containing sage, and higher in those with garlic. The 7-ketocholesterol was the cholesterol oxide found in higher amount in raw chicken on day 0, while the formation of 7β- and 7α-hydroxycholesterol was verified only from day 30 on. Cooking and storage resulted in increase of total cholesterol oxides and decrease of α- and γ-tocopherol. Sage was effective in controlling lipid and cholesterol oxidation, minimizing the prooxidant effects of salt, cooking, and storage. However, garlic presented no effect as antioxidant and accelerated lipid oxidation. PRACTICAL APPLICATION: The addition of sage to chicken meat (0.1 g/100 g) is a good alternative to prevent and delay the formation of compounds derived from lipid oxidation that are responsible for off-flavors and loss of nutritional quality during long-term frozen storage. Care must be taken when using garlic to seasoning chicken meat products, such as hamburgers and meatballs, especially cooked or precooked due to its potential to promote lipid oxidation and consequently raising the risk of having the product rejected by the consumer.     

1H-NMR Study of Cholesterol Autooxidation in Egg Powder and Cookies Exposed to Adverse Storage

The level of cholesterol oxides depends on the production and storage conditions for food. We studied the effect of prolonged storage, heat, and diffuse daylight on spray-dried egg powder and cookies containing large amounts of cholesterol. The cholesterol oxides were isolated by chromatographic procedures, and were identified by recording ¹H-NMR spectra of selected HPLC fractions. Autooxidation was quite slow when the sample was stored in a freezer at — 20°C. Diffuse daylight increased the amounts of β-epoxide of cholesterol, whereas heating caused a sharp increase in C-7 oxidized cholesterol derivatives. Extent of cholesterol oxidation depended on storage conditions.     

Enzymatic Determination of Cholesterol Oxides

For measurement of the concentration of oxidised cholesterols in foodstuffs, a method was developed by adapting the well-known enzymatic determination of cholesterol. A linear correlation was found between the absorbance measured after enzymatic reaction and the concentrations of 7α-hydroxycholesterol, 7β-hydroxycholesterol, 7-ketocholesterol, cholesterol-5α, 6α-epoxide in the range 1–12 μg. The usefulness of this method was demonstrated by determination of the four cholesterol oxidation products separated by TLC from the non-saponifiable lipid fraction of 5-month-old whole-egg powder (stored under different conditions) and of biscuit enriched with egg powder. The main advantages of the combination of TLC and the enzymatic method, beyond its rapidity and sensitivity, are that the determination of cholesterol oxidation products can be carried out in parallel with many samples containing small amounts of oxidised cholesterols even in the presence of a large quantity of cholesterol.     

High-Resolution NMR Detection of Cholesterol Oxides in Spray-Dried Egg Yolk

A new approach, alternative to currently available methods, for studying cholesterol oxidation in egg powder is reported. The quantitative analysis of cholesterol oxides was carried out by high-resolution proton nuclear magnetic resonance (¹H-NMR). The following oxides were isolated from spray-dried egg powder by rapid chromatographic procedures and detected by selecting “marker”¹H-NMR signals: 7-ke-tocholesterol, 7α-hydroxy-cholesterol, 7β-hydroxy-cholesterol, cholesterol-α-epoxide and cholesterol-β-epoxide. The quantified cholesterol derivatives ranged from 4.9 to 9.1 ppm with a detection limit of 0.3 ppm (5 μ.g from 16g of matrix). The main usefulness of the method should be in investigating intermediates and products due to chemical transformation of cholesterol during storage and heating of foodstuffs.