In-line preconcentration of oxidized and reduced glutathione in capillary zone electrophoresis using transient isotachophoresis under strong counter-electroosmotic flow

Transient isotachophoresis (tITP) can improve the sensitivity of capillary electrophoresis (CE). In general, it was carried out under the condition of suppressed electroosmotic flow (EOF). However, some special conditions, such as extreme low pH background electrolyte and coating were needed to achieve the requirements of suppressed EOF. In this work, an approach of tITP under the strong counter-EOF in open system (counter-EOF-tITP) is presented for the rapid and sensitive preconcentrating the reduced glutathione (GSH) and the oxidized glutathione (GSSG) without modifying the capillary and the commercial CE instrument. The parameters of the experimental system, such as the concentration of leading electrolyte, the injected amount of terminating electrolyte and the injected pressure of sample were investigated in detail to understand the mechanism of counter-EOF-tITP. The sensitivity enhancement factors were of 320 for GSH and 280 for GSSG. In addition, the detection limit of 23.4 and 18.0 μg L⁻¹ for GSH and GSSG was achieved, respectively. The method's applicability was demonstrated by determining GSH and GSSG in tomato and human serum.     

Application of multiple headspace-solid-phase microextraction followed by gas chromatography–mass spectrometry to quantitative analysis of tomato aroma components

The objective of this paper is to investigate the potential of multiple headspace-solid-phase microextraction (MHS-SPME) for the determination of volatile compounds in complex matrix samples. A method based on MHS-SPME for the determination of around 20 volatile compounds, responsible of tomato flavour and aroma has been developed and validated, using gas chromatography with mass spectrometry (ion trap analyser) for analysis. For this purpose, the experimental β parameter, resulting from the MHS-SPME theoretical development, has been obtained from real sample analysis (in triplicate) for each identified compound, carrying out up to 5 consecutive extractions. Later, this parameter is used to perform quantitation of real samples after just a single HS-SPME extraction. Precision, expressed as repeatability, has been evaluated by analysing six replicates of a real sample, showing relative standard deviations between 4 and 20%. For accuracy study, quantitative results have been compared with those obtained by means of standard additions on replicate samples, and no statistically significant differences between the two methods were observed. Since MHS-SPME uses the estimated total area corresponding to the complete extraction of compounds (obtained from the β parameter), quantitation can be carried out by external calibration using standards in solvent and splitless injection, instead of by SPME. Linearity, tested in the range 0.05–15 μg/mL, showed satisfactory values, with coefficients of correlation between 0.995 and 0.999. Limits of detection were in the range of 0.25–5 ng/g. MHS-SPME has been proved to be an adequate technique to avoid matrix effects in complex samples quantitation. Its applicability to the determination of volatile tomato components, together with its limitations, is discussed in this article.     

Differentiation of the volatile profile of microbiologically contaminated canned tomatoes by dynamic headspace extraction followed by gas chromatography-mass spectrometry analysis

The aromatic profile of microbiologically contaminated canned tomatoes was analyzed by the dynamic headspace extraction technique coupled with gas chromatography-mass spectrometry. Canned tomatoes contaminated with Escherichia coli, Saccharomyces cerevisiae and Aspergillus carbonarius were analyzed after 2 and 7 days. About 100 volatiles were detected, among which alcohols, aldehydes and ketones were the most abundant compounds. Gas chromatographic peak areas were used for statistical purposes. First, principal component analysis was carried out in order to visualize data trends and clusters. Then, linear discriminant analysis was performed in order to detect the set of volatile compounds ables to differentiate groups of analyzed samples. Five volatile compounds, i.e. ethanol, β-myrcene, o-methyl styrene, 6-methyl-5-hepten-2-ol and 1-octanol, were found to be able to better discriminate between uncontaminated and contaminated samples. Prediction ability of the calculated model was estimated to be 100% by the “leave-one-out” cross-validation. An electronic nose device was then used to analyze the same contaminated and not contaminated canned tomato samples. Preliminary results were compared with those obtained by dynamic headspace gas chromatography-mass spectrometry, showing a good agreement.     

微波消化、ICP-AES测定蕃茄粉中 8种微量元素

以微波消化蕃茄粉,电感耦合等离子体-原子发射光谱(ICP-AES)快速测定样品中的8种微量元素,各元素的相对标准偏差均小于3%,回收率在95.9%-102.7%之间,方法简便、快速,准确度高,结果令人满意.     

波长比和近红外光谱的番茄品质检测方法

番茄的可溶性固形物(SSC)、pH值和坚实度(Firmness)是决定番茄的口感及收获后品质的主要因素。提出一种基于波长比和近红外光谱的番茄SSC,pH和坚实度检测方法。首先用Vis/SWNIR便携式光谱仪 (波长：400～1 100 nm)和中波近红外便携式光谱仪 (波长：900～1 683 nm)在相互作用模式下,对6个不同成熟度的600个番茄样本进行光谱采集,对所采集的光谱用波长比法和波长比+自动缩放法进行预处理后,分别建立番茄SSC,pH和坚实度的预测模型,比较单一自动缩放、单一波长比、波长比+自动缩放及不做预处理四种方法的预测结果。结果显示,波长比法结合自动缩放预处理可有效提高可见/短波近红外光谱对SSC,pH和坚实度的预测精度(r_p=0.779,0.796和0.917);波长比法+自动缩放法可提高中波近红外光谱对SSC的预测效果(r_p=0.818)。这说明波长比法在优化和处理番茄光谱信息方面具有一定的潜力。     

固相萃取-高效液相色谱测定番茄中的赤霉素GA3残留

建立了固相萃取-高效液相色谱(SPE-HPLC)法分析番茄中赤霉素GA3残留量的方法.研究了不同填料的固相萃取小柱对番茄中赤霉素的萃取回收率以及各自的纯化结果.该方法线性范围为0.21～1.05×102mg/L,检出限为0.011mg/kg,在优化条件下,以C18小柱萃取样品的效果最好,加标回收率为88.45%～95.90%,其RSD为1.15%～6.56%.     

空间分辨光谱和可见/近红外光谱的番茄颜色等级判别

比较分析空间分辨光谱和单点可见/近红外光谱（可见/短波近红外光谱和中波近红外光谱）对番茄颜色的识别能力。根据番茄表面和内部颜色将600个样品分为6个等级（green, breaker, turning, pink, light red和red）。分别利用新型空间分辨光谱系统（550~1 650 nm）,可见/短波近红外光谱仪（400~1 100 nm）和中波近红外光谱仪（900~1 700 nm）采集番茄的空间分辨（spatially-resolved, SR）光谱和单点可见/近红外（SP Vis/NIR）光谱,建立番茄等级的偏最小二乘判别（PLSDA）模型,比较其对番茄颜色等级的预测效果。结果表明, SR光谱组合可在最佳单一SR光谱基础上进一步提高番茄颜色的识别能力,对番茄表面颜色和内部颜色的识别率可分别达到98.8%和84.6%。光源-检测器距离较近的SR光谱对番茄表面颜色的识别有帮助,而光源-检测器距离较远的SR光谱能较好的判别番茄内部颜色。SP NIR光谱在对番茄表面颜色判别中与SR光谱具有一定可比性,其分类准确率可达到95%,但SP Vis/NIR光谱在对番茄内部颜色识别中具有较低的分类准确率,分类结果远不如SR光谱,说明SR光谱比SP Vis/NIR光谱对番茄颜色的判别更具潜力。     

90°束旋转环形非稳腔几何特性分析

分析了ＵＲ９０环形非稳腔（ＵｎｓｔａｂｌｅＲｅｓｏｎａｔｏｒｓｗｉｔｈ９０°ＢｅａｍＲｏｔａｔｉｏｎ）正向模和反向模的几何特性，讨论了反向模无阻挡时的振荡条件，并导出了理想ＵＲ９０环形非稳腔的光线追述方程，考查了此腔对激光增益介质的空间自平均效应。     

Automated evaluation of food colour by means of multivariate image analysis coupled to a wavelet-based classification algorithm

This paper describes an approach for the colour-based classification of RGB images, taken with a common digital CCD camera on inhomogeneous food matrices. The aim was that of elaborating a feature selection/classification method independent of the specific food matrix that is analysed, in the sense that the variables that are the most relevant ones for the classification of the analysed samples are selected in a blind way, with no a priori assumptions on the basis of the nature of the considered food matrix. A one-dimensional signal describing the colour content of each acquired digital image, which we have called colourgram, is created as the contiguous sequence of the frequency distribution curves of the three red, green and blue colours values, of related parameters (also including hue, saturation and intensity) and of the scores values deriving from the PCA analysis of the unfolded 3D image array, together with the corresponding loadings values and eigenvalues. Once a sufficient number of digital images has been acquired, the corresponding colourgrams are then analysed by means of a feature selection/classification algorithm based on the wavelet transform, wavelet packet transform for efficient pattern recognition (WPTER). This approach was tested on a series of samples of “pesto”, a typical Italian vegetable pasta sauce, which presents high colour variability, mainly due to technological variables (raw materials, processes) and to the degradation of chlorophylls during storage. Good classification results (100% of correctly classified objects with very parsimonious models) have been obtained, also in comparison with the visual evaluation results of a panel test.     

舌尖上的化学——酱油那些事儿

As an old saying goes: "firewood, rice, oil, salt, sauce, vinegar, tea", as one of the most popular seasonings in the kitchen, soy sauce brings us rich taste experience every day. In order to give readers a more comprehensive and in-depth understanding of this condiment that is closely related to our lives, this paper introduces the history of soy sauce, brewing technology and the formation principle of color and flavor from the perspective of chemistry.