Facile synthesis of tomato-based carbon nanodots and its utilization in sensitive detection of tartrazine

Carbon nanodots (CDs) with superior fluorescence performance were obtained by hydrothermal method using tomatoes as raw materials. When the ultraviolet absorption band of tartrazine and the fluorescence spectrum of CDs have complementary overlaps, the fluorescent internal filter effect (IFE) occurred. Furthermore, the degree of quenching of fluorescence intensity of CDs has an excellent linear correlation with tartrazine concentration. And based on this principle, a method for detecting tartrazine was established. As the decrease of fluorescence intensity, tartrazine can be measured in the linear range of 0.1 μM–40 μM. The detection limit is 39 nM, and the recovery rate is 90.7%～114.5%. The established protocol was also effectively employed to assay tartrazine in beverage samples, indicating that it has great potential for food color analysis.     

Separation of pectin methylesterase isoenzymes from tomato fruits using short monolithic columns

One of the main forms of tomato pectin methylesterase (PME; EC 3.1.1.1.1) that is applicable to the food industry was isolated from fresh tomato fruit. The extraction of the PME isoenzymes involved washing the fresh tomato flesh with water in order to remove sugars and than solubilizing the enzymes with a diluted HCl solution at pH 1.6. The extract was then neutralized to pH 7.4 using buffer solution. After filtration, the solution was directly fractioned using Convective Interaction Media (CIM) short monolithic disk column bearing sulfonyl (SO3) groups and using a linear gradient from 0 to 700 mM NaCl. The injection volume was 3 ml and the diameter of the column was 12 mm and length 3 mm. The isolated fractions were monitored for protein content and PME activity. The fraction with the targeted enzyme, which showed NaCl independent activity, was further purified and concentrated by ultrafiltration and finally purified by a second semi-preparative cation-exchange chromatography step using a CIM carboxymethyl (CM) disk monolithic column consisting of two disks and applying a step gradient. From 1 kg of fresh tomato fruits, 7.5 mg of purified PME with molecular mass estimated to be 26 000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was obtained. A fraction with mixed PME and polygalacturonase activity was also obtained. Compared to the published procedures for the isolation and purification of PME from plant materials, this new procedure is much faster and more efficient. The potential application of CIM disk short monolithic columns in the analysis and semi-preparative extraction and isolation of the PME isoenzyme is presented.     

Squeezing flow of semi liquid foods between parallel Teflon coated plates

Samples of commercial tomato paste, low fat mayonnaise and mustard about 6–8 mm thick were squeezed to 0.8 mm at various speeds between 5 mm min⁻¹ and 25 mm min⁻¹ between Teflon-coated parallel plates 127 mm in diameter using an Instron UTM Model 5542. All the log force vs log height relationships had a clearly identified linear region. This indicated that a dominant squeezing flow regime was achieved at about 3 mm height, and that the machine has the proper stiffness to perform the tests. The stress level at a pre-selected height in this region is a measure of consistency, sensitive enough to distinguish between products of different brands. The residual stress after relaxation for about 2 min was on order of 10–50% of the initial stress, an indication that all three foods have a considerable structural integrity. In all three products there was a considerable discrepancy between the observed rate effects and predictions based on a pseudoplastic (power law) model. It could be described by the empirical relation (F_v1 − F_R)/(F_v2 − F_R)=(V₁/V₂)^m where F_v1 and F_v2 are the forces at the given displacement reached at speeds v₁ and v₂ respectively, F_R is the residual force after relaxation (found to be practically rate independent), and m is a constant of the order of 0.15–0.33, independent of the compression velocities ratio but characteristic of the food and brand. The calculated elongational viscosity was not a unique function of biaxial strain rate. To a certain extent, this was probably due to imperfect lubrication. But it was also a manifestation of these products considerable structural integrity which cannot be accounted for by models developed for ideal liquids. Received: 1 November 1999 Accepted: 2 May 2000     

基于近红外特征光谱的番茄苗氮含量快速测定方法研究

为了提高近红外光谱技术快速测定番茄苗氮含量的准确度和稳健性, 比较分析竞争自适应重加权采样法(CARS)、蒙特卡罗无信息变量消除法(MCUVE)、向后间隔偏最小二乘法(BiPLS )和组合间隔偏最小二乘法(SiPLS)四种特征波长挑选方法, 筛选与番茄苗氮含量相关的特征光谱。在十种不同氮素处理水平下(尿素溶液浓度0～120 mg·L-1), 培育60株番茄苗样本(每个处理6株), 使其分别处于不同程度的过量氮素、氮素适度、缺氮素和无氮素状态。分别采集每株番茄苗样本的叶片, 扫描其12 500～3 600 cm-1波段的近红外光谱。比较四种方法所建立的番茄苗氮素定量分析模型可知: CARS和MCUVE挑选的特征变量所建定标模型的性能比BiPLS和SiPLS挑选的特征变量所建定标模型的性能更优, 但是预测性能远低于后者。其中, 基于BiPLS建立的番茄苗氮素含量预测模型性能最佳, 相关系数(r)、预测均方根误差(RMSEP)和性能对标准差之比(RDP)分别为0.952 7, 0.118 3和3.291 0。因此, 近红外光谱技术结合特征谱区筛选可以有效地提高番茄苗叶片氮素含量的定量分析模型指标, 使模型更实用化。但是, 特征波长挑选方法不具有普适性。基于单个波长变量筛选的方法所建立的模型较为敏感, 更适用于样本状态较为均匀的待测对象;而基于波长区间筛选的方法所建的模型相对抗干扰性更强, 更适用于样品状态不均匀, 重现性较差的待测对象。因此, 特征光谱筛选只有与样本状态及建模指标结合, 才能使其在建模过程中发挥更好的作用。     

Determination of photoirradiated high polar benzoylureas in tomato by HPLC with luminol chemiluminescence detection

This study reports the first analytical application of luminol chemiluminescence reaction for the sensitive detection of two benzoylurea insecticides (diflubenzuron and triflumuron). Off-line experiments demonstrated that previously irradiated traces of these benzoylurea insecticides largely enhanced the chemiluminescence emission yielded from the oxidation of luminol in methanol:water mixtures, by potassium permanganate in alkaline medium, the enhancement being proportional to the concentration of both pesticides. The two benzoylureas were determined in tomato samples by coupling liquid chromatography with post-column photoderivatization and detection based on this chemiluminescence reaction. Tomato samples were extracted using the QuEChERS method based on extraction with acetonitrile and dispersive solid-phase clean-up using primary and secondary amine (PSA). Interferences due to matrix effect were overcome by using matrix-matched standards. The optimised method was validated with respect to linearity, limits of detection and quantification, precision and accuracy. Under the optimised conditions, calibrations graphs were linear between 0.05 and 0.50 μg mL⁻¹ for diflubenzuron and between 0.10 and 1.00 μg mL⁻¹ for triflumuron. Method detection limits were 0.0025 and 0.0131 μg mL⁻¹ (equivalent to 0.0005 and 0.0026 mg kg⁻¹) and quantification limits were 0.05 and 0.10 μg mL⁻¹ (equivalent to 0.01 and 0.02 mg kg⁻¹) for diflubenzuron and triflumuron, respectively. In both cases, quantification limits were lower than the maximum residue levels (MRLs) established by the European legislation. The relative standard deviation of intra-day precision was below 10% and recoveries were between 79.7% and 94.2% for both pesticides.     

废弃番茄叶中叶绿素超声-微波协同的提取工艺

利用超声-微波协同法提取废弃番茄叶中的叶绿素.通过单因素及正交试验研究了溶剂、乙醇浓度、微波功率、超声温度、超声时间、料液比、微波时间7个因素对叶绿素提取量的影响,再进行正交试验和验证实验.结果表明最佳工艺条件是:乙醇浓度90％、微波功率500W、超声温度70℃、超声时间40min、料液比1∶10(g/mL)、微波时间...     

Multivariate curve resolution modeling of liquid chromatography-mass spectrometry data in a comparative study of the different endogenous metabolites behavior in two tomato cultivars treated with carbofuran pesticide

A metabonomic study based on the application of multivariate curve resolution and alternating least squares (MCR-ALS) to three-way data sets obtained by liquid chromatography coupled to mass spectrometry detection (LC-MS) was carried out for Rambo and Raf tomato cultivars treated with carbofuran pesticide. Samples were picked up during a 21 days period after treatment and analyzed by LC-MS in scan mode, along with the corresponding blank samples. Then, MCR-ALS was applied to the three-way data sets using column wise augmented matrices, and the evolutionary profiles as a function of the time after treatment were estimated for the metabolites present in both cultivars, as well as their corresponding pure spectra estimations. A comparative study using those estimations showed that some of these metabolites followed different behavior for the different cultivars after treatment. Since all treated and untreated Rambo and Raf samples were picked up according to the same sampling protocol and in a similar state of maturation, any difference in the behavior between profiles can be interpreted as an effect due to the presence of pesticide and to the kind of cultivar. Based on this hypothesis, several PLS-DA approaches were tested to check if it would be possible to classify samples by using the metabolites MCR estimations. Results showed that PLS-DA models for classification of treated or non-treated (blank) samples were the best ones obtained (98.44% of correct classifications for the validation set), which supports the stress effects related to carbofuran treatment. In addition, excellent discrimination among the four groups could be attained (89.06% of correct classifications for the validation set).     

基于光谱的春季育苗移栽期番茄苗健壮度量化检测

为了筛选影响春季育苗移栽期番茄穴盘苗健壮程度的关键指标,并实现其快速无损检测,测定了5项秧苗指标,经向量归一化预处理并采用独立性权系数法确定各指标权重,并根据权重结果挑选出包含信息较全面,影响较大的两个指标：叶绿素和干质量。两项指标所组成的简化秧苗评价值可以近似表示综合评价值,相关系数r为0.92,大大减少了品质检测所需的指标量,并可以很好的表征春季育苗移栽期番茄苗的健壮度。提取了各穴盘苗的可见-近红外光谱数据,经去噪和多元散射矫正（MSC）预处理,消除了由光散射等带来的光谱干扰信息,相较原始光谱信息更具可利用性。随后采用光谱-理化值共生距离（SPXY）算法对样本集进行划分,利用波段值和评价值两种变量同时计算样本间距离,以最大化表征样本分布,提高样本差异性和代表性。采用竞争性自适应重加权算法（CARS）和无信息变量消除连续投影算法（UVE-SPA）优选光谱特征波数,降低光谱数据维度,得到了更能体现光谱特征的简化光谱信息,减少了冗余信息对建立模型精准度和分析速度的影响。最后应用偏最小二乘支持向量机（LS-SVM）和基于U-Net模型改造的卷积神经网络(CNN),以预处理后的光谱数据和提取特征波长后的光谱数据分别作为模型的输入,建立了光谱数据与综合评价值的非线性映射模型,并进行对比选优。结果显示：应用UVE-SPA预处理方法筛选出的波段,光谱信息更加丰富有效;两种预处理后的优选波段所建模型回归效果整体优于全波段建立的模型;CNN模型的建模效果整体优于LS-SVM模型,且UVE-SPA-CNN模型对光谱数据和秧苗评价值的回归分析效果最好,其建模集和预测集的相关系数r分别为0.988和0.946,均方根误差RMSE分别为0.085和0.025,为直接利用光谱数据获取融合了多种因素的番茄秧苗评价值,从而判别秧苗健壮度提供了理论依据。     

Direct Analysis of Thallium in Solid Samples of Bovine Liver and Tomato Leaves by Laser Excited Atomic Fluorescence Spectrometry Using a Graphite Furnace

Laser excited atomic fluorescence spectrometry (LEAFS) with a N₂-laser pumped dye laser with a Shimadzu GFA-4A graphite furnace is used to determine thallium in solid samples of bovine liver and tomato leaves. The linear range for thallium under the studied conditions is 0–50 pg. The instrumental LEAFS detection limit for thallium was 100 fg. Solid samples from National Institute of Standards and Technology were analyzed by this method. The content of thallium in bovine liver and tomato leaves was 0.059 and 0.055 μg/g with relative standard deviation of 12.5% and 15.8% respectively; the results obtained are within the reported limit.