纳米金/石墨烯修饰电极测定食品中的诱惑红

利用滴涂法制备石墨烯修饰电极,采用电化学还原法将纳米金粒子修饰到石墨烯修饰电极的表面,制备了纳米金/石墨烯修饰电极。研究诱惑红在纳米金/石墨烯修饰玻碳电极上的电化学行为,建立一种测定食品中诱惑红含量的新方法。结果表明,在pH=5.0的磷酸盐缓冲溶液中,-0.8⁰.8 V电位范围内,诱惑红在纳米金/石墨烯修饰玻碳电极上出现一对可逆的氧化还原峰,纳米金/石墨烯修饰玻碳电极对诱惑红的电化学反应具有很好的电催化作用;在8.00×10^-81.00×10^-5mol/L的范围内,氧化峰电流与诱惑红浓度成线性关系,检出限为8.00×10^-9mol/L。该修饰电极具有良好的灵敏度、选择性和稳定性,可用于食品中诱惑红含量的测定,回收率在96.9%¹01.6%之间,因此该方法可以用于测定食品中诱惑红的含量。      

Application of gold nanoparticles/TiO2 modified electrode for the electrooxidative determination of catechol in tea samples

A gold nanoparticles/TiO(2) composite modified Indium tin oxide (ITO) electrode has been constructed to study the electrochemical behaviour of catechol (CC) and hydroquinone (HQ) using cyclic voltammetry and differential pulse voltammetry (DPV). Increasing of separation of the oxidative peak potentials and peak current for CC and HQ in pH 6.0 phosphate buffer solution (PBS), make it suitable for selected determination of CC. After the optimization of the conditions, CC was determined by DPV and the linear range is from 1.0×10(-7) to 5.0×10(-4) mol L(-1) with a correlation coefficient of 0.999 and limit of detection as 5.0×10(-8) mol L(-1). Interference and stability study showed a satisfactory result. The proposed method has been applied to determine catechol in tea samples, and comparing with the chromatography the results are satisfactory.     

Electrochemical sensor based on graphene and mesoporous TiO2 for the simultaneous determination of trace colourants in food

Currently, synthetic colourants draw much attention as food additives. This paper investigated the simultaneous electrocatalytic oxidation of sunset yellow and tartrazine, two yellow colourants commonly present in food together, with a novel voltammetric sensor based on graphene and mesoporous TiO₂ modified carbon paste electrode. Due to the high accumulation effect and great catalytic capability of graphene and mesoporous TiO₂, the developed sensor exhibited well-defined and separate square wave voltammetric peaks (i.e., 272 mV) for sunset yellow tartrazine. The peak currents of sunset yellow and tartrazine increased linearly with their concentration in the ranges of 0.02–2.05 μM and 0.02–1.18 μM, respectively. And the detection limit was 6.0 and 8.0 nM for sunset yellow and tartrazine, respectively. This new sensor was applied to determine sunset yellow and tartrazine in several food sample extracts. Results suggested that the proposed sensor was sensitive, rapid and reliable.     

Migration of titanium dioxide from PET/TiO2 composite film for polymer-laminated steel

PET/TiO₂ composite film is the most widely used film for polymer-laminated steel, and the migration of TiO₂ is very important for the safety evaluation of its packaged food. Microwave digestion, wet digestion and dry ashing were used for pretreatment of composite film to determine the content of TiO₂ in composite film. Migration tests were carried out at 40°C, 60°C and 80°C 4% using acetic acid and 50% ethanol as the acid and ester food simulants. The migration amount of TiO₂ was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). With increasing temperature and time, the migration of TiO₂ increased. In 4% acetic acid, the migration amount of TiO₂ at 40°C for 10 days was 1.88 mg kg^?1 and the migration amount at 80°C for 8 h was 3.32 mg kg^?1, indicating that the effect of temperature on migration was more obvious. Under the same conditions, the migration amount of TiO₂ in 4% acetic acid was greater than in 50% ethanol. X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) were used to analyse the crystal structure, morphology, chemical groups and thermal properties of the film before and after the migration tests. The results showed that filmTiO₂ had a stable rutile type crystal structure and it was almost uniformly distributed. PET and TiO₂ were combined with strong chemical bonds. After TiO₂ migration, the crystallinity and the glass transition temperature (Tg) of the film decreased, but the change of melting temperature (Tm) was not obvious.     

Electrochemical behaviour of Sudan I at Fe3O4 nanoparticles modified glassy carbon electrode and its determination in food samples

In this work, a simple and sensitive electrochemical method was developed to determine Sudan I based on magnetic Fe₃O₄ nanoparticles modified glassy carbon electrode using cyclic voltammetry and differential pulse voltammetry. The sensor exhibited an obviously electrocatalytic activity towards the oxidation of Sudan I, which can be confirmed by the increased oxidation peak current and the decreased oxidation peak potential when compared with the bare GCE. The determination conditions, such as pH, modifier amount, accumulation time and accumulation potential, were optimised. And some kinetic parameters were calculated. Under the optimum experimental conditions, the oxidation current of Sudan I was proportional to its concentration from 0.01 to 1 μM and 1 to 20 μM. The detection limit was estimated to be 0.001 μM (S/N = 3). The developed method was successfully applied to determine Sudan I content in food samples with satisfactory results.     

二硫化钼负载纳米金粒子修饰电极测定酱油中曲酸

目的 建立二硫化钼负载纳米金粒子(MoS2/gold nanoparticles, MoS2/AuNPs)修饰电极快速测定酱油中曲酸的方法。方法 采用柠檬酸钠还原氯金酸的方法制备纳米金颗粒, 采用恒电位沉积法制备二硫化钼负载纳米金粒子的修饰电极。研究曲酸在不同修饰电极上的电化学行为, 探讨缓冲溶液类型、pH、MoS2用量和沉积时间对曲酸电化学行为的影响。结果 在5~500 μmol/L范围内, 曲酸浓度与峰电流呈现良好的线性关系, 回归方程为ipa (μA)=0.00952C (μmol/L)-0.21898, r2=0.99345。检出限为3.9 μmol/L, 回收率为97.2%~105.5%, 相对标准偏差小于8.0%。结论 本方法所构建的修饰电极具有较好的抗干扰性、重现性和稳定性, 适用于酱油样品中曲酸的分析。     

Use of titanium dioxide (TiO2) photocatalysts as alternative means for Listeria monocytogenes biofilm disinfection in food processing

The aim of this work was to study the photocatalytic activity of titanium dioxide (TiO₂) against Listeria monocytogenes bacterial biofilm. Different TiO₂ nanostructured thin films were deposited on surfaces such as stainless steel and glass using the doctor-blade technique. All the surfaces were placed in test tubes containing Brain Heart (BH) broth and inoculated with L. monocytogenes. Test tubes were then incubated for 10 days at 16 °C in order to allow biofilm development. After biofilm formation, the surfaces were illuminated by ultraviolet A light (UVA; wavelength of 315-400 nm). The quantification of biofilms was performed using the bead vortexing method, followed by agar plating and/or by conductance measurements (via the metabolic activity of biofilm cells). The presence of the TiO₂ nanoparticles resulted in a fastest log-reduction of bacterial biofilm compared to the control test. The biofilm of L. monocytogenes for the glass nanoparticle 1 (glass surface modified by 16% w/v TiO₂) was found to have decreased by 3 log CFU/cm² after 90 min irradiation by UVA. The use of TiO₂ nanostructured photocatalysts as alternative means of disinfecting contaminated surfaces presents an intriguing case, which by further development may provide potent disinfecting solutions. Surface modification using nanostructured titania and UV irradiation is an innovative combination to enhance food safety and economizing time and money.     

Optimization of wool mothproofing with nano TiO2 using statistical analysis

Wool, with excellent characteristics, has the problem of being fed on by the moth. Until now several chemicals have been introduced for mothproofing with some limitations. In this research, an optimized mothproofing of wool has been proposed with nano TiO₂ and citric acid by using Design-Expert software. Mothproofing was statistically investigated by measuring wool weight loss during feeding by the larvae of carpet beetle, Anthrenus verbasci. The analysis of variance was applied to obtain the optimum conditions for mothproofing. The damage intensity of wool fabrics was also observed with a digital camera. Further, the dyeing properties of the treated wool fabrics were examined through evaluating exhaustion of CI Acid Blue 113. Finally, the wool fabrics treated with optimized concentration of CA and 1.2% TiO₂ nanoparticles indicated the best protection against moths.     

Criteria to define a more relevant reference sample of titanium dioxide in the context of food: a multiscale approach

ABSTRACT

Titanium dioxide (TiO₂) is a transition metal oxide widely used as a white pigment in various applications, including food. Due to the classification of TiO₂ nanoparticles by the International Agency for Research on Cancer as potentially harmful for humans by inhalation, the presence of nanoparticles in food products needed to be confirmed by a set of independent studies. Seven samples of food-grade TiO₂ (E171) were extensively characterised for their size distribution, crystallinity and surface properties by the currently recommended methods. All investigated E171 samples contained a fraction of nanoparticles, however, below the threshold defining the labelling of nanomaterial. On the basis of these results and a statistical analysis, E171 food-grade TiO₂ totally differs from the reference material P25, confirming the few published data on this kind of particle. Therefore, the reference material P25 does not appear to be the most suitable model to study the fate of food-grade TiO₂ in the gastrointestinal tract. The criteria currently to obtain a representative food-grade sample of TiO₂ are the following: (1) crystalline-phase anatase, (2) a powder with an isoelectric point very close to 4.1, (3) a fraction of nanoparticles comprised between 15% and 45%, and (4) a low specific surface area around 10 m² g^–1.     

A novel nanosensor based on Pt:Co nanoalloy ionic liquid carbon paste electrode for voltammetric determination of vitamin B9 in food samples

In this work we describe a novel nanoalloy (Pt:Co) room temperature ionic liquid (RTIL) modified carbon paste electrode as a high sensitive sensor for voltammetric determination of vitamin B₉ in food samples. The sensor exhibits an enhanced effectiveness for the electro-oxidation of vitamin B₉ in aqueous solution. The oxidation peak potential for this matter at a surface of the ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) Pt:Co carbon paste electrode (Pt:Co/IL/CPE) appeared at 685 mV that was about 110 mV lower than the oxidation peak potential at the surface of the traditional carbon paste electrode (CPE) under similar condition. The mechanism of the electro-oxidation process on the surface of the modified electrode was analyzed. Square wave voltammetry (SWV) was applied as a very sensitive electrochemical method for the determination of sub-micro-molar amounts of vitamin B₉. The linear response range and detection limit were found to be 1.0 × 10⁻⁷ to 5.0 × 10⁻⁴ M and 4.0 × 10⁻⁸ M, respectively. The prepared modified electrode shows several advantages such as simple preparation method, high stability, high sensitivity, and excellent catalytic activity, long-term stability and remarkable voltammetric reproducibility for eletrooxidation of vitamin B₉. The proposed sensor was successfully applied for the determination of vitamin B₉ in food samples.     

Application of flow injection analysis to determine protein-bound nitrite in meat products

The development and application of a methodology based on flow injection analysis (FIA) for the determination of protein-bound nitrite (PBN) in meat products was studied. Since the FIA methodology used for measuring residual nitrite was not appropriate for determining PBN (even at a concentration of 15.9 mg of PBN/kg) in meat products, the procedure was modified and then studied for residual nitrites and PBN. Ammonium chloride (A), which is used conventionally (the original FIA method), was replaced by different carriers (the modified FIA method): B (buffer 7); C (buffer 7.5); D (buffer 8); E (NaOH 0.5 M) and F (NaOH 1 M). Carriers B and C provided the lowest limits of quantification of residual nitrite, lower than that obtained using the original FIA method. The method for determining PBN in several meat products (frankfurter and dry sausages) was validated by comparing it with the method usually used. The results obtained indicate that the modified FIA method (with carriers B and C) can be used as a simple, easy, fast, accurate and precise methodology for quantifying residual nitrite and PBN in meat products.     

Study on the properties of woolen fabric treated with chitosan/TiO2 sol

In order to improve the color yield and color fastness to light, woolen fabrics were treated with chitosan and TiO₂ sol at first, and then dyed using C.I. Acid Blue 7 dye. The woolen fabric samples before and after treatment were investigated by means of scanning electron microscope and energy dispersive spectroscopy, thermal analysis, and Fourier transform infrared spectroscopy. The reflectance spectrum, color yield K/S value and color fastness to light were also measured. The results show that compared with the untreated woolen fabric, the thermal stability of woolen fabric treated with chitosan/TiO₂ sol is improved. The protection against ultraviolet radiation, color yield K/S value, and color fastness to light are also improved.     

Modified Rice Straw as a Template in Syntheses of Nano TiO2 Loaded on Wool Fibers for Wastewater Treatment

Industrialization of textile produces large amounts of colored wastewater and recycling of that wastewater is recently under the scope. The current work is implemented to use rice straw as a template for preparation of nano TiO₂ to be applied in decolorization of wastewater of textile industries. Different treatments including silica removal and esterification were performed for rice straw to produce highly reactive nanotitanium dioxide. Size, morphological shape, and surface area of the so obtained TiO₂ nanoparticles were observed to be influenced by rice straw treatments. Percentage of anatase phase in titanium dioxide was increased from 41.6% to 75.0% after removing of silica and modification with citric acid of rice straw. The particle size of anatase was significantly reduced from 88.6 nm to 10.5 nm while the BET surface area of nanotitanium dioxide was enlarged from 41.2 m²/g to 84.7 m²/g. The prepared TiO₂ nanoparticles were loaded onto wool fibers and the photocatalytic properties of nano TiO₂ powder before and after loaded to fiber were measured against methylene blue dye. The dye removal percentage raised from 92.5 to 99.2 by using of nano TiO₂ powder-loaded wool fibers compared to nano TiO₂ powder.     

Simultaneous dyeing and functional finishing of cotton fabric using reactive dyes doped with TiO2 nano-sol

A new approach for simultaneous salt-free dyeing and functional finishing, i.e. UV protection and antibacterial properties of cotton fabric were studied. In this study, cotton fabric was cationized with 3-chloro-2-hydroxypropyl trimethylammonium chloride. Two types of reactive dyes (CI Reactive red 120 and CI Reactive yellow 145) were doped with different amounts (0.035, 0.053, and 0.07 mol) of TiO₂ nano-sol by sol–gel method and applied on cationized cotton fabric using pad–dry–steam method without the addition of salt. The chemical and morphological structures of the dyed fabrics were characterized by attenuated total reflection-Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. Different properties were investigated such as color strength, fixation, fastness properties (washing, rubbing, and light), UV blocking, antibacterial activity, and tensile strength. Samples dyed with titanium dyeing solutions exhibited better antibacterial efficacy and durable UV protection, with minimal impact on color depth and tensile strength compared with the samples dyed with commercial reactive dyes.     

Rapid,simple and sensitive determination of the apparent formation constants of trans-resveratrol complexes with natural cyclodextrins in aqueous medium using HPLC

The study of the complexation of trans-resveratrol with natural cyclodextrins (CDs) in aqueous medium under different physico-chemical conditions of pH or temperature is essential if this antioxidant compound is to be used successfully in the food industry as ingredient of functional foods, due its poor stability, bioavailability and solubility. In this paper, a rapid, simple and sensitive determination of the apparent formation constant of trans-resveratrol/CD complexes by HPLC in aqueous medium has been investigated for first time. It can be observed that trans-resveratrol forms a 1:1 complex with α-, β- and γ-CD. The highest value of the apparent formation constant (K_F = 1922 ± 89 M⁻¹) was found for β-CD and a strong dependence of K_F on pH can be seen in the region where the trans-resveratrol begins the deprotonation of their hydroxyl groups. Moreover, an increase in the system’s temperature produced a decrease in the values of K_F. Finally, to gain information on the mechanism of the trans-resveratrol affinity for CD, the thermodynamic parameters of the complexation were obtained.     

A simple and reliable liquid chromatography-tandem mass spectrometry method for the determination of aflatoxin M1 in milk

A new chromatographic method is proposed for the analysis of aflatoxin M₁ in milk. The method is based on liquid–liquid extraction followed by LC-MS/MS analysis. Liquid–liquid extraction (LLE) is performed on the defatted milk plus sodium chloride by using ethyl acetate as an extraction solvent. Accuracy and precision were evaluated at the LOQ (15?ng?kg^–1) spiked sample as well as with three other different naturally contaminated reference materials. The mean overall recovery (n?=?24) was 95% with a confidence interval of 1.9% and a CV% of 4.5%. The performance of the proposed method was compared with that of the Official ISO Method based on the use of immunoaffinity chromatography columns (IAC): LLE protocol could be considered a valid alternative to the LC-IAC. In general it showed better accuracy with lower data dispersion. Moreover, the sample preparation is very simple and straightforward, potentially being applicable as a high-throughput method which, on account of its simplicity and low cost, may be applied to the analysis of a large number of samples in the occasion of outbreaks of large-scale contamination.     

活性炭吸附结合TiO2光催化分离纯化杨木预水解液中的木糖

利用活性炭吸附和TiO₂光催化降解脱除杨木预水解液中的溶解木素,探讨了不同活性炭类型（木质基磷酸活化活性炭、食品质303活性炭、煤质活性炭）、活性炭用量、吸附时间、光催化时间、TiO₂用量对预水解液中木素、总木糖、糠醛、羟甲基糠醛（5-HMF）以及乙酸等有机组分含量的影响,优化确定了活性炭吸附和TiO₂光催化降解条件。研究结果表明,木质基磷酸活化活性炭对木素的吸附脱除效果最好,在活性炭用量为1.0%和吸附时间为10 min时,总木糖得率为93.1%,木素、糠醛、5-HMF、乙酸脱除率分别为75.1%、29.3%、22.4%、3.5%。单一TiO₂光催化处理,在TiO₂用量1.0%和光催化时间10 h条件下,总木糖得率为89.0%,木素、糠醛、5-HMF、乙酸脱除率分别为40.2%、24.2%、32.1%、3.1%。活性炭协同TiO₂光催化处理预水解液的较优工艺条件为：木质基磷酸活化活性炭用量1.0%、光催化时间6 h和TiO₂用量0.1%~0.5%,此条件下预水解液中木素的脱除率为84.4%~86.7%,总木糖得率为88.2%~89.8%,糠醛脱除率为53.8%~65.1%,5-HMF脱除率为48.6%~51.7%,乙酸含量变化不明显 。     

Synthesis,characterisation and analytical application of Fe3O4@SiO2@polyaminoquinoline magnetic nanocomposite for the extraction and pre-concentration of Cd(II) and Pb(II) in food samples

This work describes a novel Fe₃O₄@SiO₂@polyaminoquinoline magnetic nanocomposite and its application in the pre-concentration of Cd(II) and Pb(II) ions. The parameters affecting the pre-concentration procedure were optimised by a Box–Behnken design through response surface methodology. Three variables (extraction time, magnetic sorbent amount and pH) were selected as the main factors affecting the sorption step, while four variables (type, volume and concentration of the eluent, and elution time) were selected as main factors in the optimisation study of the elution step. Following the sorption and elution of analytes, the ions were quantified by flame atomic absorption spectrometry (FASS). The limits of detection were 0.1 and 0.7 ng ml^?1 for Cd(II) and Pb(II) ions, respectively. All the relative standard deviations were less than 7.6%. The sorption capacities of this new sorbent were 57 mg g^?1 for Cd(II) and 73 mg g^?1 for Pb(II). Ultimately, this nanocomposite was successfully applied to the rapid extraction of trace quantities of these heavy metal ions from seafood and agricultural samples and satisfactory results were obtained.