洋葱状富勒烯的提纯研究

以石墨粉为碳源, Al为催化剂, 采用真空热处理法制备了平均粒径为15～35 nm的洋葱状富勒烯(OLFs).并用CS₂分离和空气氧化法对得到的OLFs初产品进行了提纯处理.高分辨透射电镜(HRTEM)、X射线衍射(XRD)、热重分析(TGA)对提纯前后样品的分析表明, CS₂分离处理可有效去除初产品中裸露的金属催化剂微粒,然后在空气中610 ℃焙烧200 min,可基本去除无定型碳,并大量去除了石墨状碎片等碳杂质, OLFs的纯度在50％(体积分数)以上.     

洋葱色素的提取及抗氧化活性的测定

分别用芬顿（Fenton）反应法和1,1-二苯-2-苦肼基（DPPH）法测定了洋葱色素的抗氧化作用。结果表明,洋葱色素对羟自由基和DPPH自由基均有一定的清除作用,其清除率大小依次为42．4％,58．2％。洋葱色素是十分具有开发利用价值的天然色素。     

洋葱中黄酮类物质的提取及抗氧化作用研究

采取热水浸提法、乙醇浸提法、纤维素酶辅助法以及超声波法从红皮洋葱中提取黄酮.研究表明超声波法提取洋葱中黄酮类物质提取率最高,可达4.3％.研究了洋葱提取物中的黄酮类物质对O2-·和·OH,的抗氧化性能,研究表明洋葱提取物中黄酮类物质的抗氧化能力较VC强,而且与VC具有很好的正协同作用.     

Monitoring of substrate and product concentrations in acetic fermentation processes for onion vinegar production by NIR spectroscopy: value addition to worthless onions

Wastes and by-products of the onion-processing industry pose an increasing disposal and environmental problem and represent a loss of valuable sources of nutrients. The present study focused on the production of vinegar from worthless onions as a potential valorisation route which could provide a viable solution to multiple disposal and environmental problems, simultaneously offering the possibility of converting waste materials into a useful food-grade product and of exploiting the unique properties and health benefits of onions. This study deals specifically with the second and definitive step of the onion vinegar production process: the efficient production of vinegar from onion waste by transforming onion ethanol, previously produced by alcoholic fermentation, into acetic acid via acetic fermentation. Near-infrared spectroscopy (NIRS), coupled with multivariate calibration methods, has been used to monitor the concentrations of both substrates and products in acetic fermentation. Separate partial least squares (PLS) regression models, correlating NIR spectral data of fermentation samples with each kinetic parameter studied, were developed. Wavelength selection was also performed applying the iterative predictor weighting–PLS (IPW-PLS) method in order to only consider significant spectral features in each model development to improve the quality of the final models constructed. Biomass, substrate (ethanol) and product (acetic acid) concentration were predicted in the acetic fermentation of onion alcohol with high accuracy using IPW-PLS models with a root-mean-square error of the residuals in external prediction (RMSEP) lower than 2.5% for both ethanol and acetic acid, and an RMSEP of 6.1% for total biomass concentration (a very satisfactory result considering the relatively low precision and accuracy associated with the reference method used for determining the latter). Thus, the simple and reliable calibration models proposed in this study suggest that they could be implemented in routine applications to monitor and predict the key species involved in the acetic fermentation of onion alcohol, allowing the onion vinegar production process to be controlled in real time.     

火焰原子吸收光谱法测定大葱中的10种金属元素

采用火焰原子吸收光谱法测定不同品种和不同产地大葱中无机元素K、Ca、Na、Mg、Fe、Mn、Zn、Cu、Cr和Cd。结果表明：不同品种和不同产地大葱中所含无机元素差异较大,这为高营养育种和强化营养栽培提供了重要参考依据。该方法的加标回收率为96.74%—107.20%,相对标准偏差（RSD）在0.44%—2.67%之间,具有良好的准确度和精密度。     

显式溶剂模型模拟嵌段共聚物在纳米微滴中的图案化结构

采用耗散粒子动力学(DPD)方法研究了嵌段共聚物在纳米微滴中的相分离行为.模拟是将共聚物纳米微滴置于溶剂环境中进行自发相分离,从而形成一些图案化结构.由于是受限体系,所形成的结构和在溶液或熔融体中形成的相分离结构有所差异,这些结构的形成与亲/疏溶剂嵌段比例(RH/T)有关系.随着亲/疏溶剂嵌段比例的增加,依次形成了枣糕球体、排球状相、多层囊泡(洋葱相)、笼状相、纳米杆状相和分散胶束等结构.我们对洋葱相的形成过程进行了详细的描述.溶剂粒子的集群属性有助于更加深入地了解洋葱相的结构衍化.采用密度曲线分析了洋葱相的结构.在较高的亲/疏溶剂嵌段的比例条件下,嵌段共聚物主要表现为亲溶剂性,通过吸收大量的溶剂溶胀形成疏松结构或瓦解形成分散的胶束悬浮在溶剂中.本文模拟结果与理论或实验结果基本吻合.     

Switching properties of free-standing epitaxial ring magnets

We present the results of a study of the magnetic switching properties of arrays of narrow Co(1 0 0) epitaxial ring magnets, with outer diameters between 1 and 2 μm, varying inner diameters and varying film thickness. We discuss measurements and the results of numerical computations of the switching fields for the transition from the vortex state to the ‘onion’ state. A large dependence on the ring width and the film thickness is found.     

Dissipative Particle Dynamics Simulation of Onion Phase in Star-block Copolymer

A dissipative particle dynamics simulation technique was used to investigate the effect of molecular architecture of star-block copolymer on the patterned structure in a nanodroplet. With increasing the ratio of solvophilic to block length to solvophobic block length(R_H/T), solvophobic sphere, ordered hexagonal phase, onion phase, perforated onion phase and flocculent phase are formed, respectively. Since onion phase has potential application in controlled drug release, it has received wide attention experimentally and theoretically. Our simulation indicates onion phase forms at a certain R_H/T(close to but less than 1). A star-block copolymer molecule has two conformations in onion phase: either fully located in a shell or shared by two neighboring shells. Central structure affects onion's final shape. The molecular number of the copolymer in each shell is a quadratic function of the shell's radius. The arm number of star-block copolymer has little influence on onion's structure, but slightly affects the solvent content. Additionally, we studied the influence of arm length on onion's structure.     

用气-质联用技术检测葱、蒜、韭菜中多种农药残留量时试样预处理方法

采用气相色谱及质谱联用技术,测定葱、蒜及韭菜等蔬菜中多种农药残留量时,在粉碎试样之前,用磷酸或微波加热处理试样,可使蒜酶钝化并消除其基体干扰。试验结果显示,或用磷酸处理,或经微波加热处理,均能有效消除高背景的干扰。试样在粉碎前经磷酸预处理,在所测定的75种农药中有90％以上农药的回收率达到70％～120％之间。     

Pungency evaluation of onion cultivars from the Venezuelan West-Center region by flow injection analysis-UV-visible spectroscopy pyruvate determination

A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars (Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min⁻¹, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L⁻¹ and hydrochloric acid concentration 0.5 mol L⁻¹. The working calibration range was extended from 80 mg L⁻¹ (Batch method) to 700 mg L⁻¹ with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r² = 0.8353. Significant differences (P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid.