荷移光度法测定谷物中嘌呤含量的实验

探讨荷移光度法测定谷物嘌呤的方法。通过筛选得到适宜测定嘌呤的荷移剂为氯醌酸,并对氯醌酸荷移光度法测定嘌呤的条件做了探究,所得最优测定条件为:室温(20～30℃)、pH中性、以无水乙醇为介质、控制测定体系水分2. 5%～3. 0%、反应5～30 min,得到n_(氯醌酸)∶n_(鸟嘌呤)=1∶3的紫红色稳定荷移络合物;在λ_(max)=532 nm下,鸟嘌呤和混合总嘌呤浓度在0～1×10~(-4)mol·L~(-1)范围内符合朗伯-比耳定律且有良好的线性关系,其线性方程分别为ΔA_(鸟嘌呤)=0. 034c_(鸟嘌呤)+0. 005 (R~2=0. 995 2)、ΔA_(总嘌呤)=0. 028 5c_(总嘌呤)+0. 0071 (R~2=0. 992),其摩尔吸光系数分别为ε_(鸟嘌呤)=3. 1×10~4L·mol~(-1)·cm~(-1)、ε_(总嘌呤)=3. 6×10~4L·mol~(-1)·cm~(-1),检出限分别为2×10~(-6)mol·L~(-1)、9×10~(-6)mol·L~(-1)。而对谷物实样的测得结果显示本实验所建立方法有良好的精密度(RSD 2. 2%～7. 3%)且与HPLC法(RSD 2. 2%～7. 5%)相一致,回收率为83. 8%～98. 1%与HPLC法的91. 8%相当,符合GB/T 27417—2017对微量成分分析的要求,且经F-检验和t-检验均表明本法与HPLC法无统计学上差异。因此,用氯醌酸荷移光度法测定谷物中的嘌呤含量可行。     

基于高倍富集放大反应的双点电位滴定法测定谷物中氟含量

【目的】饮食中氟可影响人体健康与安全,简捷准确检测饮食中氟含量就显得十分重要。【方法】以现有GB/T 5009. 18-2003的氟离子电极电位滴定法为基础,以高倍富集放大反应为获得高灵敏度的突破点,以双点电位滴定法为确保方法准确的手段,探寻出灵敏准确测定谷物中微量氟的新方法。以方法的检测限(LOD)、加标回收率和相对标准偏差(RSD)等为衡量指标,通过单因素试验法对影响富集反应的富集剂种类、用量、温度、时间、反应体系酸度(pH)、搅拌速率和洗涤次数等因素考察后,针对富集反应主要影响因素富集剂用量、反应温度、反应时间和反应体系酸度(pH)等用L₉(3^₄)正交试验优化获得最适宜的测定条件。【结果】所得最适宜条件为：含Ca^₂₊复合富集剂用量为(m_氟/m_复合剂) = 1:1×10^₅,反应时间200min,反应温度22℃,反应体系酸度pH 5.5,搅拌速率200~300 r/min,沉淀物洗涤4次。该法的LOD_F = 5.3×10^_-3 μg/g,且c_F在1.0×10^_-6 mol/L ~ 1.0×10^_-1 mol/L内呈良好定量函数关系：E = 38.657 lgc - 174.44 (R2 = 0.996)。加标回收率为91.5 %~100.3 %,测定结果较稳定(RSD≤2.7%)。实样氟含量测定值符合GB 2762-2005氟限量要求。【结论】本法集合了富集反应的高倍放大的效果和双点电位滴定法的高精准的特点,测定选择性高,速度快,灵敏度较高,是种实用可靠的微量氟的定量分析方法。且有易于实现自动化和智能化快捷在线检测的潜能。     

仿刺参精、卵多肽体外抗氧化及对H2O2诱导巨噬细胞氧化损伤的保护作用

目的 为研究仿刺参精、卵多肽体外抗氧化及对H₂O₂诱导巨噬细胞氧化损伤的保护作用。方法 采用切向流超滤法对多肽进行分级制备,通过测定清除1,1-二苯基-2-苦基苯肼自由基(DPPH.)、羟基自由基(.OH)和超氧阴离子自由基(O_2^-.)的能力来评价体外抗氧化活性,并对多肽的相对分子质量(Mr)、氨基酸(AA)组成及氧化稳定性进行检测分析,通过构建氧化损伤细胞模型,考察多肽对H₂O₂诱导RAW 264.7巨噬细胞氧化损伤的保护作用。结果 仿刺参精、卵多肽均具有较强的清除DPPH.、.OH和O_2^-.能力,并且在一定范围内呈现量效关系,Mr<1×10^₃ Da的多肽AJS1和AJE1抗氧化活性表现更强,两者Mr 95.56%和91.89%在1×10^₃ Da以内,疏水性AA和酸性AA比例均较高,并具有极佳的耐盐性和热稳定性,但在贮存和加工过程中仍要注意过酸环境和金属离子对氧化稳定性的影响。所有多肽组对巨噬细胞不存在毒性影响,并且多肽质量浓度为200、400 μg/mL时均对H₂O₂损伤的RAW 264.7巨噬细胞体现出显著的保护作用(P<0.05)。结论 仿刺参精、卵多肽具有良好的体外抗氧化和对氧化损伤细胞的保护作用,具有开发为功能性食品、医药和化妆品等的潜力。     

高效液相色谱法同时测定面粉及面粉改良剂中的曲酸和噻二唑

建立高效液相色谱法(HPLC)同时测定面粉及面粉改良剂中的曲酸和噻二唑。方法 色谱柱Atlantis C₁₈(4.6 mm ×15 cm,5 μm),流动相组成为乙腈-0.1%磷酸溶液,梯度洗脱,流速1.0 ml/min,进样体积1 μl,曲酸和噻二唑的检测波长分别为269和300 nm。样品以乙腈提取,提取液经离心、滤过后供HPLC分析。结果 曲酸、噻二唑均在0.5～20 μg/ml范围内线性关系良好,平均加标回收率为84.2%～92.4%,RSD为1.1%～6.9%(n=6),检出限(LOD)分别为2.0和0.7 mg/kg。结论 该方法可用于面粉和面粉改良剂中曲酸和噻二唑的测定。     

微咸水灌溉条件下施用不同改良剂对盐渍化土壤盐分离子分布的影响--测试文章

利用5种不同的土壤改良剂,对矿化度在2～3 g·L^-1的微咸水灌溉棉田土壤进行改良效果研究。结果表明：五种改良剂均降低土壤pH值和总盐含量,并能有效控制土体Na⁺、Ca²⁺、SO₄^2-、HCO₃^-积累;其中,磷石膏能显著降低土体Na⁺、Ca²⁺、SO₄^2-总含量（P＜0.05）,DS1997能显著降低土体Na⁺、HCO₃^-总含量（P＜0.05）,酸碱平衡剂显著降低土体Ca²⁺、SO₄^2-总含量（P＜0.05）,禾康改良剂有效控制土体SO₄^2-、HCO₃^-含量;改良剂对土体中Cl^-改良效果不显著（P＞0.05）。研究得出：微咸水灌溉导致土壤pH值升高和含盐量增加,造成土壤盐分的积累;土壤改良剂可有效减少微咸水灌溉引起的盐分积累,改善土壤理化特性和盐分离子分布。     

基于刃天青的电化学方波伏安法快速鉴别大肠杆菌的耐药性

目的：评价5株食源性大肠杆菌临床分离株对环丙沙星、庆大霉素和氨苄西林的抗生素耐药性。方法：基于细菌能量代谢过程中的电子传递理论,引入刃天青作为氧化还原探针,建立了一种基于刃天青介导的大肠杆菌耐药性快速鉴别的电化学方波伏安法（square wave voltammetry,SWV）。结果：在1.69×10²～1.69×10⁸ CFU/mL范围内,大肠杆菌浓度与刃天青氧化峰电流（I）之间存在较好的线性关系,回归方程为Y=-0.156 0X-2.965 5,R²=0.977 5;在进行大肠杆菌耐药性测定时,参考美国临床和实验室标准协会制定的药敏试验标准,以刃天青的氧化峰电流（I₀）和大肠杆菌直接与刃天青作用后得到的氧化峰电流（I_-a）作为对照,测定大肠杆菌用抗生素处理后与刃天青作用得到氧化峰电流（I_+a）,引入细菌活性值V_ETA作为电化学方波伏安法鉴别细菌耐药性的指标,建立了刃天青介导的大肠杆菌电化学快速药敏试验方法;运用建立的方法检测了5种食源性大肠杆菌临床分离株对3种抗生素的耐药性,以V_ETA=50作为判断细菌敏感和耐药的临界值,均得到与纸片扩散法结果相符的药敏试验结果,而纸片扩散法报告结果需18 h,该法仅需2 h。结论：建立的基于刃天青介导的大肠杆菌耐药性快速鉴别的电化学方波伏安法能够准确且快速检测5株食源性大肠杆菌临床分离株对环丙沙星、庆大霉素和氨苄西林的抗生素耐药性。     

大豆荚甾醇提取动力学与热力学的研究

研究了用乙醇溶液从大豆荚中提取甾醇。通过预实验,选定合适的提取条件,测定了提取液中甾醇质量浓度随提取温度和提取时间的变化;将获得的实验数据进行了模型拟合;计算了动力学参数和热力学参数。结果表明：高的提取温度可获得快的提取速度和高的平衡质量浓度;提取过程符合一级平板动力学模型;研究条件下提取过程的表观活化能为22.47 kJ/mol;内扩散系数在1.04×10_^-10 m_²/min到2.45×10_^-10 m_²/min的范围内随提取温度升高而增大;半衰期随提取温度升高而从17.3 min降至4.1 min;吉布斯自由能均小于零,表明甾醇提取过程为自发过程;提取过程焓变为35.16 kJ/mol、熵变为125.8 J/(mol.K),过程吸热、熵增。所得结果可为业界提供参考。     

二甲四氯异辛酯及其代谢物二甲四氯在玉米中的残留量及风险评估

目的 明确鲜食玉米和成熟期籽粒中2甲4氯异辛酯及其代谢物2甲4氯残的残留水平,评价其膳食摄入风险。方法 以改进的QuEChERS前处理方法同时提取玉米中2甲4氯异辛酯和2甲4氯残留物,分别用用气相色谱-串联质谱法和液相色谱-串联质谱法检测2甲4氯异辛酯和2甲4氯的残留量。结果 2甲4氯异辛酯和2甲4氯仪器最小检出量(LOD)分别为2×10_^-12 g和5×10_^-12 g;在鲜食玉米、成熟期籽粒的最小检出浓度( LOQ)均为0.005 mg/kg,整体回收率为71%~114%,相对标准偏差(RSD)为1.2%~7.2 %。结论 该方法的准确度和精密度良好,2甲4氯异辛酯在鲜食玉米中残留量为<0.005~0.032 mg/kg,成熟期籽粒中残留量为<0.005~0.022 mg/kg,均<0.05 mg/kg;代谢物2甲4氯在鲜食玉米、成熟期籽粒中的最终残留量均<0.005 mg/kg;玉米中2甲4氯异辛酯及其代谢物2甲4氯残的膳食风险较低。     

柴油植物毛榛种仁油性质分析

本文参照我国国标规定的油脂性质的测定方法,测定了非粮柴油植物毛榛种仁的含油量、酸值、碘值、皂化值、水分及挥发物含量、折光指数、脂肪酸组成,结果表明毛榛种仁含油50.61%、密度917.0kg.m_-3、酸值0.9183mg.g_-1、碘值100.8g.(100g)_-1、皂化值179.0mg.g_-1,碳链长度主要集中在C14-C20之间,不饱和脂肪酸占90%以上,以油酸(C₁₈H₃₄O₂)和亚油酸(C₁₈H₃₂O₂)为主,分别为60.49%和28.72%。多元不饱和脂肪酸中三烯脂肪酸(亚麻酸)含量为0.56%,不含四烯及四烯以上脂肪酸。结果表明：毛榛种仁油性质优良,可作为北方地区重点开发的生物柴油原料植物。     

CO2浓度升高对不同水分养分条件下小麦幼苗生长的影响--测试文章

设置了5个氮素浓度梯度（N₀、N₁、N₂、N₃、N₄）、3个PEG（P₀、P₁、P₂）浓度梯度以及2个CO₂浓度（370±50 μmol·mol^-1; 700±50 μmol·mol^-1）水平的盆栽试验,探究了小麦幼苗生长、物质积累与分配以及植株水分条件的变化规律。结果表明：小麦幼苗株高、地上部干重、根干重、生物量以及叶水势的最大值以及高浓度CO₂的最大刺激作用均出现在处理N₁P₀; 而根长和根冠比的最大值分别出现在处理N₀P₀和N₁P₂,高浓度CO₂的最大刺激值也分别出现在处理N₀P₀和N₁P₂; 适宜养分条件下,高浓度CO₂能够最大限度地促进小麦幼苗的生长,同时高浓度CO₂通过提高小麦幼苗叶水势,一定程度上缓解了低浓度PEG胁迫的不利影响。因此,未来CO₂浓度升高将对水肥条件好的小麦产生促进作用,可缓解轻度水分不足的不利影响,而对严重干旱胁迫下小麦的生长作用不明显。     

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.     

An internet compendium of analytical methods and spectroscopic information for monomers and additives used in food packaging plastics

An internet website (http://cpf.jrc.it/smt/) has been produced as a means of dissemination of methods of analysis and supporting spectroscopic information on monomers and additives used for food contact materials (principally packaging). The site which is aimed primarily at assisting food control laboratories in the European Union contains analytical information on monomers, starting substances and additives used in the manufacture of plastics materials. A searchable index is provided giving PM and CAS numbers for each of 255 substances. For each substance a data sheet gives regulatory information, chemical structures, physico-chemical information and background information on the use of the substance in particular plastics, and the food packaging applications. For monomers and starting substances (155 compounds) the infra-red and mass spectra are provided, and for additives (100 compounds); additionally proton NMR are available for about 50% of the entries. Where analytical methods have been developed for determining these substances as residual amounts in plastics or as trace amounts in food simulants these methods are also on the website. All information is provided in portable document file (PDF) format which means that high quality copies can be readily printed, using freely available Adobe Acrobat Reader software. The website will in future be maintained and up-dated by the European Commission's Joint Research Centre (JRC) as new substances are authorized for use by the European Commission (DG-ENTR formerly DGIII). Where analytical laboratories (food control or other) require reference substances these can be obtained free-ofcharge from a reference collection housed at the JRC and maintained in conjunction with this website compendium.     

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.     

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.     

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.     

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.