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。     

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。     

胆固醇氧化物的鉴定、制备及其对大鼠肝细胞的毒性

本文用气相色谱-质谱联用仪对胆固醇高温氧化物进行鉴定,采用硅胶柱色谱法对氧化物进行分离,并由MTT法检测其对大鼠肝细胞BRL的毒性。结果显示:胆固醇在高温下的主要氧化物有5种,分别为: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。单因素实验表明在160℃下加热30 min可以产生最大量的胆固醇氧化物,并在此条件下对胆固醇氧化物进行制备。粗制品经过硅胶柱色谱洗脱收集,可得纯度约为90%的胆固醇氧化物(组成为:7α-羟基胆固醇9.96%、7β-羟基胆固醇23.24%、5,6β-环氧基胆固醇15.34%、5,6α-环氧基胆固醇14.36%、7-酮基胆固醇26.77%、胆固醇3.12%、其它杂质7.21%)。MTT法实验结果表明纯化后的胆固醇氧化物在80μg/m L浓度下对大鼠肝细胞BRL表现出显著毒性作用(p0.05),在100μg/m L时,细胞活性仅有空白对照的7.49%,胆固醇氧化物的毒性机理有待进一步研究。     

抗氧化剂对胆固醇高温氧化抑制作用研究

探讨了11种抗氧化剂对胆固醇在空气和猪油中高温氧化的抑制作用以及对猪油过氧化值的影响。使用气相色谱-质谱联用技术检测高温氧化前后胆固醇含量变化,同步检测5种主要高温氧化产物(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)。结果表明:多种抗氧化剂对胆固醇在空气中的高温氧化可以起到明显的抑制作用,以芦丁、槲皮素、绿原酸、咖啡酸效果最好。胆固醇在猪油中氧化程度较弱,11种抗氧化剂中只有咖啡酸表现出较好的抑制作用。过氧化值的对比研究发现:咖啡酸、橙皮素、柚皮素、维生素E、BHT均有一定的降低过氧化值作用,其中以咖啡酸效果最佳。不同抗氧化剂对空气中胆固醇高温氧化的抑制有很大不同,从而有助于筛选具有较强高温抗氧化能力的抗氧化剂。咖啡酸的高温抗氧化能力值得关注。     

毛细管气相色谱法测定烤鱼片中胆固醇氧化产物

应用毛细管气相色谱法检测烤鱼片中胆固醇氧化物含量。采用自装微型固相萃取柱(Microsolid-PhaseExtraction,MSPE)分离、富集样品中胆固醇氧化物。鱼片中共检出胆固醇氧化物5种,检出限分别为7β-羟基胆固醇:0.28μg/g,5β,6β-环氧化胆固醇:0.40μg/g,5α,6α-环氧胆固醇:0.16μg/g,3β,5α,6β-胆甾烷三醇:0.25μg/g,7-酮基胆固醇:0.38μg/g。线性范围在0.28～2.62μg/g之间,相关系数均大于0.9960。     

气相色谱-质谱联用法测定水产加工品中胆固醇氧化物的研究

建立了一种加速溶剂萃取-凝胶色谱净化-气相色谱/质谱联用法快速测定水产加工品中胆固醇氧化物含量的分析方法。采用此分析方法,测定了胆甾烯酮、7β-羟基胆固醇、5β,6β-环氧化胆固醇、5α,6α-环氧化胆固醇、20α-羟基胆固醇、3β,5α,6β-胆甾烷三醇、6-酮基胆固醇、7-酮基胆固醇等8种化合物,优化了加速溶剂萃取仪、凝胶净化色谱仪、气相色谱/质谱联用仪的条件,在10~1000 ng/m L范围内,线性相关系数可达0.9995以上;重现性良好,其相对标准偏差小于7%;回收率可达76%~103%;其灵敏度高,方法检测限低:8种胆固醇氧化物为0.1μg/kg以下,适用于水产加工品中胆固醇氧化物的检测工作。     

微生物转谷氨酰胺酶催化乳清蛋白聚合研究

采用SDS－PAGE分析，研究了不同条件下微生物转谷氨酰胺酶（MTGase）催化乳清蛋白（WPI）聚合。结果显示，MTGase可催化乳清蛋白的β－乳球蛋白（β-LG）和α－乳清蛋白（α－LA）聚合，形成低聚物或生物聚合物，其中β-LG更易受MTGase的催化，当TGase酶浓度一定时（0.5U/mL),TGase催化WPI聚合的最佳底物质量分数范围为2％－4％，对WPI进行加热预处理，同时添加还原剂，可明显提高MTGase对WPI的催化活性，MTGase催化WIP的最适PH值范围为6．5－7．5，当WPI经预热处理（85℃，15min），同时添加20mmol/L的DTT，TGase催化WPI聚合12h，可使质量分数为92％的β-LG和质量分数为75％的α－LA聚合。     

干腌火腿中胆固醇氧化物含量研究

胆固醇由于含有不饱和键,极易发生自动氧化,产生胆固醇氧化物(Cholesterol Oxidation Products,COPs)。生物学研究表明COPs具有细胞毒性、致突变性和致癌性。干腌火腿因其加工周期长,腌制过程中过量的食盐、脱水、适宜的温度以及长期暴露在空气中等因素都会促进胆固醇氧化,并形成COPs。采用气相色谱-质谱联用法测定干腌火腿中COPs含量。结果表明,新鲜火腿和陈放一年的火腿肌肉组织中COPs总量分别为0.59 mg/kg和2.12 mg/kg,其中7-酮基胆固醇含量最高;脂肪组织中COPs总量分别为2.49 mg/kg和4.14 mg/kg,其中胆甾烷-3β,5α,6β-三醇和7-酮基胆固醇含量较高。     

利用胆固醇氧化酶转化胆固醇制备胆甾-4-烯-3-酮

用酶法催化氧化胆固醇制备胆甾-4-烯-3-酮相对于化学法合成具有反应简单、成本较低等优点.作者探讨了在正辛烷作为有机相的两相反应体系中,以胆固醇氧化酶催化氧化胆固醇制备胆甾-4-烯-3-酮的方法.在胆固醇质量浓度为40g/L,反应时间40min、反应温度40℃、磷酸缓冲液-正辛烷体积比32、通氧40L/h及搅拌转速300r/min下,胆固醇转化率达到92%,经薄板层析及紫外扫描,发现转化产物为单一的胆甾-4-烯-3-酮.     

热处理延长油茶籽油氧化稳定性研究

研究了油茶籽经过不同条件加热后其压榨油氧化稳定性的变化规律,并通过测定压榨油过氧化值、酸值、水分、脂肪酸、油脂伴随物等指标探讨影响油茶籽油氧化稳定性变化的主要因素。结果表明,油茶籽经过不同温度加热20 min后,其压榨油的氧化稳定时间显著延长,30、60、90、120、150℃加热条件下分别比初始延长了1.1、4.2、5.2、3.5、3.9倍,随着加热时间的延长,60、90℃和120℃的加热温度下油茶籽油的氧化稳定性变化趋于平缓,30℃和150℃下加热40 min后氧化稳定性仍有提高,在加热60 min时,5种温度氧化稳定时间分别比初始延长了4.4、5.0、4.4、3.1、5.8倍。水分、酸值、过氧化值、角鲨烯含量、β-谷甾醇含量与油茶籽油的氧化稳定性的变化呈现负相关,说明水分、酸值、过氧化值低的油茶籽油的氧化稳定性好,角鲨烯和β-谷甾醇等抗氧化物质并不是提高油茶籽油氧化稳定性的活性成分。总酚、5-丁基二氢-2(3H)-呋喃酮、3,4-二甲基-2,5-二氢呋喃、正辛醇、苯甲醛、戊酸、辛酸、苯乙醛、壬醛等物质的含量与油茶籽油的氧化稳定性呈现正相关,说明总酚和美拉德反应产物可能是延长油茶籽油氧化稳定性的主要因素。     

高活性胆固醇氧化酶产生菌出发菌株的筛选

从4个不同来源的样品中筛选出高产胞内胆固醇氧化酶的出发菌株,经鉴定为假单胞菌属.用五种处理方法对细胞进行破壁,使其释放出胞内酶,结果表明,超声波处理胞内酶破壁效果较好,最高酶活可达到63.9u/g湿菌体.     

生物方法降低食品中胆固醇的研究趋势

利用生物方法降低食品中胆固醇的途径一般有两种;一是微生物的直接培养;二是利用微生物胆固醇氧化酶（EC1．1．3．6）的转化作用。本文对比了两种途径并认为后者具有效率高和产物单一的特点,在实际中应用潜力较大;阐述了蛋黄和乳中胆固醇的酶法转化作用;并对今后该领域的研究方向提出了建议。     

低聚果糖降血脂作用的动物研究

为探讨低聚果糖对高脂动物血脂的影响,以高脂饲料诱发大鼠为高脂动物模型,同时给予高脂饲料与低聚果糖28d后,与高脂模型组比较.0.5、1.5、2.5g/kgBW低聚果糖可显著降低大鼠血清总胆固醇(TC)和甘油三脂(TG)的水平(P＜0.05);但对高密度脂蛋白胆固醇(HDL-C)的水平无显著影响.结果表明低聚果糖可降低高脂动物血脂水平.     

Ultrasonic-assisted enzymatic degradation of cholesterol in egg yolk

An ultrasonic-assisted enzymatic process was developed for effective degradation of cholesterol in natural egg yolk. The objective of this study was to follow the catalytic activity of cholesterol oxidase against egg yolk cholesterol in an effort to obtain a cholesterol reduced egg yolk without affecting the major nutrients composition of egg yolk. Cholesterol oxidase was used to catalyze the degradation of cholesterol in egg yolk. Firstly, a 30 g portion of the egg yolk was pretreated by ultrasonic for 15 min at 200 W and then incubated for 10 h with cholesterol oxidase concentration of 0.6 U/g egg yolk at 37 °C. Finally, the cholesterol level in egg yolk was reduced to 8.32% of its original concentration without affecting the quality attributes of the yolk.

Industrial relevance

With the increase of public awareness to the dangers of cholesterol in recent years, a large number of popular food products have drawn criticism for containing high levels of cholesterol. Many reduced cholesterol egg products have been developed for market requirement. The results indicate that the ultrasonic-assistant extraction is an effective method for effective degradation of cholesterol in natural egg yolk. The knowledge gained from this study should be useful for further exploitation and application of the resource. Cholesterol-reduced egg yolk promises to be a value-added functional food with all the health enhancing attributes associated with egg yolk.     

Cholesterol oxide, cholesterol, total lipid and fatty acid contents in processed meat products during storage

The effects of storage time on the formation of cholesterol oxides and on alterations in the fatty acid composition of processed meat products manufactured by Brazilian industries were investigated in this study. Cholesterol oxides and cholesterol were determined by HPLC using photodiode array and refractive index detectors. Samples of jerked beef, Italian-type salami, chicken mortadella and Chester mortadella were analysed at 30 day intervals starting at zero time, for 90 days for the mortadella and 120 days for the jerked beef and salami. The mortadellas were stored under refrigeration at 6 °C and the jerked beef and salami at room temperature, but protected from the light. No cholesterol oxides were formed during the storage time in any of the samples. The cholesterol content, the fatty acid composition and total lipid contents showed no significant differences during storage with the exception of the total lipid content of the jerked beef, which varied from 3.5 at zero time to 2.4 g/100 g after 120 days storage.     

燕麦对高胆固醇血症中老年妇女血脂水平的影响

目的:观察食用燕麦对患高胆固醇血症中老年妇女血脂水平的影响。方法:参考《中国成人血脂异常防治指南》中的判断标准,筛选高胆固醇血症中老年妇女111名,随机分为2组,分别为燕麦组,每人每天给予100g即冲即食燕麦片;对照组,每人每天给予100g普通挂面。试验周期6周,研究开始前和6周后对两组受试者进行基本健康状况问卷调查、人体测量、血生化检测以及膳食调查。结果:燕麦组52人,对照组49人完成研究。实验期间两组人员的能量、蛋白质、脂肪、碳水化合物摄入量无显著差异,但燕麦组膳食纤维摄入量明显增加,且增加幅度显著大于对照组(P0.05)。与实验前相比,试验结束时燕麦组人员的腰围、血清TC、LDL-C、ApoB以及LDL-C/HDL-C、ApoB/ApoA比值显著降低,P0.05;对照组血清HDL-C、ApoB水平显著降低,P0.05,体重、体质指数、血清TC/HDL-C、LDL-C/HDL-C比值则显著升高(P0.05)。此外,燕麦组和对照组人员的空腹血糖水平都显著降低(P0.05)。结论:在目前城市居民的膳食结构下,食用一定量的全谷类食物燕麦能够有效地降低血清胆固醇和低密度脂蛋白胆固醇水平。     

Assimilation of cholesterol and probiotic characterisation of yeast strains isolated from raw milk and fermented foods

In this study, cholesterol assimilation ratios and some probiotic characteristics of yeasts were investigated. For this purpose, yeasts were isolated from milk and foods that were naturally fermented and not containing starter culture. In vitro cholesterol assimilation properties were determined in media. The Cholesterol assimilation by yeast strains ranged between 1.36 and 73.33%. Twenty‐one yeast strains showing high assimilation percentage were selected, and their acid tolerance, bile tolerance, bile salt deconjugation activity and survival in simulated gastrointestinal conditions were investigated. Among the strains assessed, 12 of them showed probiotic characteristics.     

The effect of heat treatment on the cholesterol oxides,cholesterol, total lipid and fatty acid contents of processed meat products

The effects of heat treatment on the formation of cholesterol oxides and on alterations of fatty acid composition were investigated in processed meat products. Meatballs (beef), hamburger (beef and Chester), sausage (pork, chicken and Chester) and frankfurter (mixed meat, chicken and Chester) were analysed. There was no cholesterol oxide formation caused by heat treatment of the samples analysed. The fatty acid compositions, calculated as g/100 g sample, showed alterations only between the raw and grilled beef hamburger. Only the cholesterol levels were significantly changed when comparing the raw and grilled pork sausages and the raw and grilled Chester hamburger, the values being lower in the grilled samples. Also, the total lipid contents of grilled beef hamburgers were lower than the values.     

Determination of cholesterol in dairy products by infrared techniques: 2. FT-NIR method

A Fourier transformed near-infrared (FT-NIR) method for rapid determination of cholesterol in dairy products was demonstrated. FT-NIR spectrum of pure cholesterol was characterized and the region between 3550 and 3650 cm⁻¹ was found to be the most significant in cholesterol content determination. The FT-NIR method was found to accurately predict the cholesterol content in a variety of dairy products with r ² value greater than 0.98 and SEP estimates of less than 1.70. The FT-NIR procedure with suitable multivariate statistical model was further validated by recovery studies and compared with a conventional method. Results indicate that FT-NIR has the potential for rapid estimation of cholesterol.     

Determination of cholesterol in dairy products using infrared techniques: 1. FTIR spectroscopy

A Fourier transformed infrared (FTIR) spectroscopic method is described to estimate cholesterol after a single step extraction instead of the conventional colorimetric method. FTIR spectrum of pure cholesterol was characterized and the region between 2800 and 3200 cm⁻¹ was used for quantitative estimation. Partial least square (PLS) and principal component regression (PCR) analysis were used for quantitative analysis. FTIR spectroscopy with chemometrics could predict the cholesterol content accurate to an r ² greater than 0.99 and a standard error of prediction (SEP) of less than 0.98. The developed model was successfully applied to predict cholesterol in commercial dairy products and validated with standard method and recovery studies. Results indicate that FTIR spectroscopy can determine the cholesterol content in dairy products in approximately 5 min.