同位素稀释质谱法测定乳及含乳饮料中的酪蛋白含量

目的建立同位素稀释质谱法对以牛乳、乳粉为原料的饮料中4种不同亚型的酪蛋白进行含量测定。方法样品溶解后,经等电点沉淀法提取其中的酪蛋白,将样品复溶液稀释至适当浓度,取适量稀释液同时混入多肽同位素内标,加入胰蛋白酶酶解16 h,使用甲酸停止酶解反应,定容后离心,取上清液分析;以WATERS ACQUITY UPLC HSS T3(2.1 mm×50 mm,1.8μm)作分析柱,用0.3%(V:V)甲酸-水和乙腈作为流动相,梯度洗脱分离。质谱采用ESI正离子模式检测,多反应监测模式进行采集,内标法定量分析。结果 4种不同亚型的酪蛋白特征肽段在4 min内达到基线分离,αs1-酪蛋白、β-酪蛋白、κ-酪蛋白在0.05~8μmol/L浓度范围内线性良好,αs2-酪蛋白在0.01~5μmol/L浓度范围内线性良好,相关系数均在0.9990以上。αs1-酪蛋白、β-酪蛋白、κ-酪蛋白的方法检出限均为3 nmol/L,定量限均为10 nmol/L,αs2-酪蛋白的方法检出限为1.6 nmol/L,定量限为5 nmol/L。阴性基质加标的复溶液中,β-酪蛋白浓度在0.5、2.0、5.0μmol/L 3个水平下的平均回收率为62.21%~84.36%,相对标准偏差为3.37%~5.50%。采用该方法分别测定了豆奶粉、白咖啡饮品和液体乳饮料中的酪蛋白含量,结果表明3种样品中均含有4种不同亚型的酪蛋白,且含量各不相同。结论该方法灵敏度高、特异性强,可以准确快速地测定乳及含乳饮料中酪蛋白含量。     

酪蛋白沉淀测定方法在市售纯牛乳中的应用与验证

为了改进乳品中蛋白质含量的测定方法,在酪蛋白测定方法的前期研究基础上,增加了NaOH溶液碱复溶酪蛋白等电点沉淀物,结合凯氏定氮法对2种市售纯牛乳中的乳蛋白组分进行了测定。实验结果表明,酪蛋白质量分数约为61%,酪蛋白和乳清蛋白相加得到的理论蛋白质含量与实际测定的总蛋白质质量分数误差不超过1.38%,改进后的等电点沉淀分离结合凯氏定氮法高效准确,重现性好,可以用于纯牛乳中酪蛋白的掺假鉴定。     

等电点沉淀结合凯氏定氮法测定市售纯牛奶中酪蛋白的含量

在酪蛋白测定方法的前期研究基础上,对等电点沉淀法进行改进,结合凯氏定氮法对市售纯牛奶中的乳蛋白组分进行了测定。确定了制备纯品酪蛋白的最佳洗涤剂和洗涤次数,NaOH溶液碱复溶酪蛋白等电点沉淀物最佳添加范围。实验结果表明,改进后的等电点沉淀方法,测定酪蛋白质量分数都在74%~76%。pH4.6HAc-NaAc缓冲溶液作为洗涤剂,对于体系pH的维持更加稳定。仅沉淀的处理方式可以将大部分乳清蛋白和酪蛋白进行分离。NaOH溶液最佳添加范围是25mL~35mL。改进后的等电点沉淀结合凯氏定氮法高效准确,简单易行,重现性好,可以用于纯牛奶中酪蛋白的掺假鉴定。     

高效液相色谱法测定婴幼儿配方乳粉中酪蛋白磷酸肽的含量

目的建立高效液相色谱法测定婴幼儿配方乳粉中酪蛋白磷酸肽含量的方法。方法对婴幼儿配方乳粉样品对应生产批次所采用的酪蛋白磷酸肽原料进行测定,得到准确含量后作为参照品,对婴幼儿配方乳粉样品测定前处理中净化、提取条件进行优化,采用二极管阵列检测器(diode array detector, DAD)定量分析。结果采用混合型阳离子交换(mixed cation exchange, MCX)固相萃取柱、ZORBAX Eclipse AAA色谱柱可得到良好的分离效果,酪蛋白磷酸肽在100~500μg/mL范围内线性关系良好,相关系数r^2为0.9994,检出限为0.140 mg/100 g,加标回收为81.06%~87.78%,相对标准偏差为3.64%。结论该方法前处理操作简单,具有良好的重现性和准确性,能够满足婴幼儿配方乳粉中酪蛋白磷酸肽含量的测定。     

酶的分离纯化过程中的沉淀分离技术

沉淀分离技术被广泛地用于蛋白质的分离，酶作为一种特殊蛋白质，其分离也必然用沉淀分离技术。针对沉淀分离技术在酶的提取过程中的应用概况，重点介绍了几种常用的提纯酶的沉淀方法：有机溶剂沉淀法、盐析沉淀法、等电点沉淀法、热变性沉淀法和其他方法。     

几种儿童牛奶酪蛋白含量的测定与比较

测定儿童牛奶A、儿童牛奶B、儿童牛奶C、儿童牛奶D中酪蛋白含量并比较其蛋白质含量的性价比。采用等电沉淀法从牛奶中分离出酪蛋白,得到较纯的酪蛋白,再采用双缩脲法测定样品中酪蛋白的纯度,并计算出样品中酪蛋白的性价比。儿童牛奶A、儿童牛奶B、儿童牛奶C、儿童牛奶D中酪蛋白含量分别为:1.84、2.55、2.79、2.63 g/100 m L;提取的酪蛋白样品纯度依次为:99.78%,95.05%,97.55%,96.16%;计算得出的酪蛋白性价比依次为:0.977、1.515、1.567、1.456 g/元。等电沉淀法能有效的提取牛奶中的酪蛋白,纯度较高。各品种牛奶中酪蛋白的性价比大小为:儿童牛奶C儿童牛奶B儿童牛奶D儿童牛奶A。     

4种蛋白质沉淀剂测定乳粉中非蛋白氮含量的效果

目的 通过测定乳粉中非蛋白氮含量,比较四种蛋白质沉淀剂分离蛋白质和非蛋白含氮物质的效果。方法 样品加水溶解后分别用15 % 三氯乙酸溶液、丙酮、20 %乙酸铅溶液和3 % 草酸钾-7 % 磷酸氢二钠溶液、乙酸锌溶液和亚铁氰化钾溶液沉淀蛋白质,同时用三聚氰胺做加标回收,过滤后取滤液消化定氮。结果 三氯乙酸沉淀法计算非蛋白氮含量为0.2036%±0.0002%,相对标准偏差在四种方法中最小,为0.1023%,加标回收率为96.07±2.29%;丙酮沉淀法计算非蛋白氮含量为0.0981 %±0.0050 %,加标回收率在四种方法中最低,为50.56 %±7.90 %;乙酸铅沉淀法计算非蛋白氮含量为0.1372 %±0.0012 %,加标量为79.2mg三聚氰胺/10g样品时,乙酸铅沉淀法加标回收率比三氯乙酸沉淀法更稳定,为96.57%±1.07%;乙酸锌沉淀法计算非蛋白氮含量为0.3466 %±0.0100 %,加标回收率为86.81 %±2.87 %。结论 三氯乙酸沉淀法结果准确度和稳定性较其他三种方法更好,但受到加标量的影响。     

婴幼儿配方奶粉中肌醇的液相色谱串联质谱法测定

建立了婴幼儿配方奶粉中肌醇的液相色谱串联质谱法。样品经水溶液提取,用三氯甲烷沉淀蛋白后,用液相色谱串联质谱仪(C18柱)分析,流动相为0.2%乙酸∶甲醇(98:2;体积比),流速为0.20 m L∕min,柱温为40℃,肌醇以保留时间和多反应监测离子对定性,以内标法峰面积定量。乳粉样品中肌醇的回收率是94.7%~106%,RSD为1.80%~3.73%,线性范围在0.1~2.0 mg/kg,检出限为0.1 mg/kg。该方法操作简便、快速、准确,适用于乳粉中肌醇含量的测定。     

超声水提法-ICP-MS检测配方乳粉中碘的含量

目的建立超声水提法-电感耦合等离子体质谱法(inductively coupled plasma-mass spectrometry,ICP-MS)测定配方乳粉中碘元素的含量。方法采用水直接溶解配方乳粉中碘元素并用沉淀剂沉淀蛋白,离心后取上清液用电感耦合等离子体质谱仪(ICP-MS)检测。结果本方法测定配方乳粉中碘元素含量,线性相关系数良好(R0.999),检出限为0.43 ng/m L,精密度低于3%,碘元素加标回收率在74.5%~120.5%之间。结论此方法能够准确、快速、简便地检测配方乳粉中碘元素的含量。方法重复性较好、没有复杂的前处理步骤、检测速度快、适用于大批量配方乳粉中碘元素含量的测定。     

羊乳酪蛋白的乳化性质和热稳定性研究

试验采用等电点沉淀法和高速离心法提取崂山奶山羊原料乳的酪蛋白,并对其等电点、SDS-PAGE图谱、乳化活力、乳化稳定性、浊度和热稳定性进行分析。结果表明:崂山奶山羊乳酪蛋白的等电点pH为4.10,分子量为20~40 kDa,包括α-酪蛋白、β-酪蛋白和κ-酪蛋,且β-酪蛋白含量最多。两种提取方法所得酪蛋白溶液的乳化性质和浊度具有极显著性差异(p0.01);酪蛋白的热稳定性随温度的升高而降低。相比于高速离心法,等电点沉淀法制备的酪蛋白电泳图谱条带清晰、纯度较高、热稳定性较好,且酪蛋白溶液的乳化性均一性好。     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

Chlorohydrins of bisphenol A diglycidyl ether (BADGE) and of bisphenol F diglycidyl ether (BFDGE) in canned foods and ready-to-drink coffees from the Japanese market

BADGE.2HCl and BFDGE.2HCl were determined in 28 samples of ready-to-drink canned coffee and 18 samples of canned vegetables (10 corn, 5 tomatoes and 3 others), all from the Japanese market. HPLC was used as the principal analytical method and GCMS for confirmation of relevant LC fractions. BADGE.2HCl was found to be present in one canned coffee and five samples of corn, BFDGE.2HCl in four samples of canned tomatoes and in one canned corn. No sample was found which exceeded the 1mg/kg limit of the EU for the BADGE chlorohydrins. However the highest concentration was found for the sum of BFDGE.2HCl and BFDGE.HCl.H₂O at a level of 1.5mg/kg. A Beilstein test confirmed that all cans containing foods contaminated with BADGE.2HCl or BFDGE.2HCl had at lest one part coated with a PVC organosol.     

European priorities for research to support legislation in the area of food contact materials and articles

A strong science base is required to underpin the planning and decision-making process involved in determining future European community legislation on materials and articles in contact with food. Significant progress has been made in the past 5 years in European funded work in this area, with many developments contributing to a much better understanding of the migration process, and better and simpler approaches to food control. In this paper this progress is reviewed against previously identified work-areas (identified in 1994) and conclusions are reached about future requirements for R&D to support legislation on food contact materials and articles over the next 5 or so years.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

Textural Properties of Cold-set Gels Induced from Heat-denatured Whey Protein Isolates

A 9% whey protein (WP) isolate solution at pH 7.0 was heat-denatured at 80°C for 30 min. Size-exclusion HPLC showed that native WP formed soluble aggregates after heat-treatment. Additions of CaCl2 (10–40 mM), NaCl (50–400 mM) or glucono-delta-lactone (GDL, 0.4–2.0%, w/v) or hydrolysis by a protease from Bacillus licheniformis caused gelation of the denatured solution at 45°C. Textural parameters, hardness, adhesiveness, and cohesiveness of the gels so formed changed markedly with concentration of added salts or pH by added GDL. Maximum gel hardness occurred at 200 mM NaCl or pH 4.7. Increasing CaCl2 concentration continuously increased gel hardness. Generally, GDL-induced gels were harder than salt-induced gels, and much harder than the protease-induced gel.     

Influence des ions sur le pouvoir hydratant de l'ure e: e tude sur peau de porc ex vivo

This study deals with the influence of ions (NaCl and MgSO4) in a W/O emulsion containing 10% urea. Moisturization kinetics are assessed by corneometry on pig skin ex vivo. The formula's influence on urea penetration is measured by infrared spectrometry with an ATR device and the stripping method. Corneometry and spectroscopy were chosen to record simultaneously the hydratation levels and urea localization into superficial cell layers. Urea crystallization after evaporation of emulsions and aqueous solutions is described. Results show that urea does not hydrate nor penetrate when applied to the skin through an aqueous gel. In a W/O emulsion, sodium chloride increases the ability of urea to moisturize without improving penetration. In vitro urea crystallization is disturbed by sodium chloride or magnesium sulphate for solutions and emulsions. This stabilization by ions is correlated with good moisturization values. The stabilization of urea in the solute state provided by ions increases its water epidermal binding capacity without enhancing penetration.     

Occurrence of bisphenol-F-diglycidyl ether (BFDGE) in fish canned in oil

The levels of bisphenol-F-diglycidyl ether (BFDGE) were quantified as part of a European survey on the migration of residues of epoxy resins into oil from canned fish. The contents of BFDGE in cans, lids and fish collected from all 15 Member States of the European Union and Switzerland were analysed in 382 samples. Cans and lids were separately extracted with acetonitrile. The extraction from fish was carried out with hexane followed by re-extraction with acetonitrile. The analysis was performed by reverse phase HPL C with fluorescence detection. BFDGE could be detected in 12% of the fish, 24% of the cans and 18% of the lids. Only 3% of the fish contained BFDGE in concentrations considerably above 1mg/kg. In addition to the presented data, a comparison was made with the levels of BADGE (bisphenol-A-diglycidyl ether)analysed in the same products in the context of a previous study.     

Analysis on Economic Indicators from 62 Enterprises in Printing Machinery Industry in Q1 2014

Operation of printing machine industry was still unsatisfactory in the first quarter of 2014.Analysis on operation of printing machine industry.a.Market demand was not strong;sales of product undulated and declined.According to the statistics,the total industrial output value fell by 19.28% in the first quarter of 2014 than the average quarter value in 2013; industrial added value decreased by 4.16%; sales revenue dropped by 22.83%. h. Business operation of enterprises was in poor condition. c. R＆D of new products is an important transformation guarantee for enterprises. d. To take self explore new ways upgrading advantages,and explore new ways.