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Analytica Chimica Acta (v.719, #)
Non-parametric multivariate analysis of variance in the proteomic response of potato to drought stress by Piotr Zerzucha; Dominika Boguszewska; Barbara Zagdańska; Beata Walczak (pp. 1-7).
Display Omitted► Spot detection is a serious bottleneck of analysis of 2D-electropherograms. ► Comparison of variance analysis performed for the spot and the pixel level. ► The non-parametric MANOVA is recommended as a flexible and very fast method.Spot detection is a mandatory step in all available software packages dedicated to the analysis of 2D gel images. As the majority of spots do not represent individual proteins, spot detection can obscure the results of data analysis significantly. This problem can be overcome by a pixel-level analysis of 2D images.Differences between the spot and the pixel-level approaches are demonstrated by variance analysis for real data sets (part of a larger research project initiated to investigate the molecular mechanism of the response of the potato to drought stress). As the method of choice for the analysis of data variation, the non-parametric MANOVA was chosen. NP-MANOVA is recommended as a flexible and very fast tool for the evaluation of the statistical significance of the factor(s) studied.
Keywords: Robust analysis of variance; Biomarker identification; Non-parametric MANOV; Electrophoresis
Global test for metabolic pathway differences between conditions by Diana M. Hendrickx; Huub C.J. Hoefsloot; Margriet M.W.B. Hendriks; André B. Canelas; Age K. Smilde (pp. 8-15).
Display Omitted► Goeman's global test is a group statistic for micro array data. ► This study examines if this test can be generalized for metabolomics data. ► Metabolites are grouped according to KEGG pathways. ► The goal is to determine if these groups behave different under different conditions. ► The results correspond with the physiology of the studied organisms.In many metabolomics applications there is a need to compare metabolite levels between different conditions, e.g., case versus control. There exist many statistical methods to perform such comparisons but only few of these explicitly take into account the fact that metabolites are connected in pathways or modules. Such a priori information on pathway structure can alleviate problems in, e.g., testing on individual metabolite level. In gene-expression analysis, Goeman's global test is used to this extent to determine whether a group of genes has a different expression pattern under changed conditions. We examined if this test can be generalized to metabolomics data. The goal is to determine if the behavior of a group of metabolites, belonging to the same pathway, is significantly related to a particular outcome of interest, e.g., case/control or environmental conditions. The results show that the global test can indeed be used in such situations. This is illustrated with extensive intracellular metabolomics data from Escherichia coli and Saccharomyces cerevisiae under different environmental conditions.
Keywords: Goeman's global test; Group statistic; Metabolomics; Score test; Pathway statistic
Relationship between heavy metal distribution in sediment samples and their ecotoxicity by the use of the Hasse diagram technique by Stefan Tsakovski; Błażej Kudłak; Vasil Simeonov; Lidia Wolska; Gregorio Garcia; Jacek Namieśnik (pp. 16-23).
Display Omitted► The original element of the present study is the use of Hasse diagram technique for partial ordering to explain some specific relations between the chemical indicators analysed and the ecotoxicity tests for acute and chronic toxicity. ► A reliable estimation of the pollution impact of a large environmental object (Mar Menor lagoon in Spain) is achieved. ► The specific role of each one of the five heavy metals involved (Zn, Cu, Mn, Pb, and Cd) is interpreted in connection to the additional ecotoxicity tests.Many studies assessing the quality of sediments and their pollution impact use monitoring data consisting predominantly of chemical indicators. Recently, ecotoxicity estimates have been used as very important parameters of the ecological state of sediment samples. Thus, a more complete sediment risk assessment is achieved and more reliable information on the sediment pollution history is extracted. The data interpretation could be improved if multivariate statistical techniques were applied to data classification, modelling and interpretation. The starting classification of the data was performed using self-organizing maps (SOM) approach in order to reveal specific relationship patterns for objects and for variables. The original element of the present study is the use of the Hasse diagram technique (HDT) for partial ordering in order to explain some specific relations between the chemical indicators analysed (heavy metal content in different sediment compartments) and the ecotoxicity tests for acute and chronic toxicity. In principle, a reliable estimate of the pollution impact of a large environmental object (the Mar Menor lagoon in Spain) is achieved. The specific role of each one of the five heavy metals involved (Zn, Cu, Mn, Pb, and Cd) is interpreted in the context of the additional ecotoxicity tests.
Keywords: Mar Menor lagoon; Environmental pollution hazard; Sediments; Heavy metal distribution; Ecotoxicological tests; Self organizing maps; Hasse diagram technique; Ranking; Simimarity analysis; Environmetrics
Partial least squares and random sample consensus in outlier detection by Jiangtao Peng; Silong Peng; Yong Hu (pp. 24-29).
Graphical abstractDisplay Omitted► A novel outlier detection method in partial least squares based on random sample consensus is proposed. ► The proposed algorithm repeatedly generates PLS solutions estimated from random samples and then tests each solution for the support based on PLS residuals. ► It models inlier error as an unbiased Gaussian distribution and outlier error as a uniform distribution. ► Compared with the classic PLS and robust methods such as RSIMPLS and PRM, the proposed PLSSAC method shows comparable performance.A novel outlier detection method in partial least squares based on random sample consensus is proposed. The proposed algorithm repeatedly generates partial least squares solutions estimated from random samples and then tests each solution for the support from the complete dataset for consistency. A comparative study of the proposed method and leave-one-out cross validation in outlier detection on simulated data and near-infrared data of pharmaceutical tablets is presented. In addition, a comparison between the proposed method and PLS, RSIMPLS, PRM is provided. The obtained results demonstrate that the proposed method is highly efficient.
Keywords: Partial least squares; Random sample consensus; Outlier detection; Leave-one-out cross validation
Predicting quality and sensory attributes of pork using near-infrared hyperspectral imaging by Douglas F. Barbin; Gamal ElMasry; Da-Wen Sun; Paul Allen (pp. 30-42).
.Display Omitted► We predict pork quality by using NIR hyperspectral imaging technique. ► We achieve good correlation results for color, pH and drip loss of pork meat. ► We select optimum wavelengths for multispectral NIR instruments.Many subjective assessment methods for fresh meat quality are still widely used in the meat industry, making the development of an objective and non-destructive technique for assessing meat quality traits a vital need. In this study, a hyperspectral imaging technique was investigated for objective determination of pork quality attributes. Hyperspectral images in the near infrared region (900–1700nm) were acquired for pork samples from the longissimus dorsi muscle, and the representative spectral information was extracted from the loin eye area. Several mathematical pre-treatments including first and second derivatives, standard normal variate (SNV) and multiplicative scatter correction (MSC) were applied to examine the influence of spectral variations in predicting pork quality characteristics. Spectral information was used for predicting color features ( L, a, b, chroma and hue angle), drip loss, pH and sensory characteristics by partial least-squares regression (PLS-R) models. Independent sets of feature-related wavelengths were selected for predicting each quality attribute. The results showed that color reflectance ( L), pH and drip loss of pork meat could be predicted with determination coefficients(RCV2) of 0.93, 0.87 and 0.83, respectively. The regression coefficients from the PLS-R models at the selected optimal wavelengths were applied in a pixel-wise manner to convert spectral images to prediction maps that display the distribution of attributes within the sample. Results indicated that this technique is a potential tool for rapid assessment of pork quality.
Keywords: Meat quality; Hyperspectral imaging; Partial Least Squares Regression; Sensory analysis; Pork
Application of multi-way analysis to UV–visible spectroscopy, gas chromatography and electronic nose data for wine ageing evaluation by N. Prieto; M.L. Rodriguez-Méndez; R. Leardi; P. Oliveri; D. Hernando-Esquisabel; M. Iñiguez-Crespo; J.A. de Saja (pp. 43-51).
Display Omitted► Wine samples were analytically characterised according to their ageing process. ► Signals from a sensor-based electronic nose were fused with GC–MS and UV–visible data. ► The study involved 6 periodical determinations of 20 variables on 6 different wines. ► Multi-way analysis allowed to efficiently extract the maximum information from data. ► Multi-way methods represent the most suitable tool for processing three-mode data.In this study, a multi-way method (Tucker3) was applied to evaluate the performance of an electronic nose for following the ageing of red wines. The odour evaluation carried out with the electronic nose was combined with the quantitative analysis of volatile composition performed by GC–MS, and colour characterisation by UV–visible spectroscopy. Thanks to Tucker3, it was possible to understand connections among data obtained from these three different systems and to estimate the effect of different sources of variability on wine evaluation. In particular, the application of Tucker3 supplied a global visualisation of data structure, which was very informative to understand relationships between sensors responses and chemical composition of wines. The results obtained indicate that the analytical methods employed are useful tools to follow the wine ageing process, to differentiate wine samples according to ageing type (either in barrel or in stainless steel tanks with the addition of small oak wood pieces) and to the origin (French or American) of the oak wood. Finally, it was possible to designate the volatile compounds which play a major role in such a characterisation.
Keywords: Chemometrics; Multi-way data analysis; Tucker3; Wine ageing; Electronic nose
On-line removal of redox-active interferents by a porous electrode before amperometric blood glucose determination by Chunyan Deng; Yong Peng; Lei Su; You-Nian Liu; Feimeng Zhou (pp. 52-56).
Display Omitted► The electrochemical glucose detection was carried out based on an electrochemical flow cell comprising a porous reticulated vitreous carbon (RVC) electrode and a disk electrode. ► The design is much simpler and easier to implement for real sample assays. ► The RVC electrode requires minimal cleanup and the GOD-modified electrode remains stable for a week. ► The electrochemical flow cell should be amenable for automated on-line removal of redox interferents for other types of enzyme-based biosensors.A porous reticulated vitreous carbon (RVC) electrode and a disk electrode coupled in tandem in an electrochemical flow cell has been used for electrolytic removal of interferents before amperometric glucose detection. The electrolytic efficiency at the upstream RVC electrode is 100% at a flow rate of 0.1mLmin−1 or lower. Potential interferents such as acetaminophen, ascorbic acid, and uric acid can be completely eliminated by electrolysis at the RVC electrode. A mixed monolayer comprising glucose oxidase (GOD) and ferrocenyl-1-undecanethiol preformed at the downstream gold disk electrode was used as a mediator-based amperometric glucose sensor. The dependence of the amperometric current on the glucose concentration exhibits good linearity across over three orders of magnitude. The glucose measurements were also found to be reproducible (RSD<3.5%) and accurate. Unlike the chemiluminescence method, this device obviates the use of carcinogenic substrates and the glucose sensor performance is independent of the oxygen present in sample. On the basis that the RVC electrode requires minimal cleanup and the GOD-modified electrode remains stable for a week, the electrochemical flow cell should be amenable for automated on-line removal of redox interferents for other types of enzyme-based biosensors.
Keywords: Reticulated vitreous carbon; Amperometry; Glucose; Mediator; Interference
Statistical mixture design selective extraction of compounds with antioxidant activity and total polyphenol content from Trichilia catigua by Audrey Alesandra Stinghen Garcia Lonni; Renata Longhini; Gisely Cristiny Lopes; João Carlos Palazzo de Mello; Ieda Spacino Scarminio (pp. 57-60).
Display Omitted► Statistical design mixtures was used to extract material from Trichilia catigua barks. ► Quaternary mixtures are efficient for studying total polyphenol content and antioxidant activity. ► Comparative study of the HPLC–DAD spectra indicated different types of characteristic spectra.Statistical design mixtures of water, methanol, acetone and ethanol were used to extract material from Trichilia catigua (Meliaceae) barks to study the effects of different solvents and their mixtures on its yield, total polyphenol content and antioxidant activity. The experimental results and their response surface models showed that quaternary mixtures with approximately equal proportions of all four solvents provided the highest yields, total polyphenol contents and antioxidant activities of the crude extracts followed by ternary design mixtures. Principal component and hierarchical clustering analysis of the HPLC–DAD spectra of the chromatographic peaks of 1:1:1:1 water–methanol–acetone–ethanol mixture extracts indicate the presence of cinchonains, gallic acid derivatives, natural polyphenols, flavanoids, catechins, and epicatechins.
Keywords: Catuaba; Extraction optimization; Mixture modeling; Simplex-centroid design; Trichilia catigua; barks
Fast screening of terpenes in fragrance-free cosmetics by fluorescence quenching on a fluorescein–bovine serum albumin probe confined in a drop by Noelia Cabaleiro; Inmaculada de la Calle; Carlos Bendicho; Isela Lavilla (pp. 61-67).
Display Omitted► A rapid screening of terpenes in fragrance-free cosmetics is performed. ► An aqueous drop containing fluorescein-BSA is used as a probe to extract terpenes. ► Fluorescence quenching caused by terpenesis monitored by microvolume-fluorospectrometry. ► Dilution of the cosmetic sample in 40% (v/v) ethanol is used as the only sample treatment. ► Low LODs, comparable with those obtained by sophisticated techniques such as GC–MS are obtained.A headspace single drop microextraction procedure is proposed for terpene screening in fragrance-free cosmetics. The drop is composed by an aqueous solution of a fluorescence probe formed by bovine serum albumin and fluorescein. Extracted volatile terpenes produce a fluorescence quenching that can be monitored by microvolume-fluorospectrometry. This quenching is observed on the fluorescein fluorescence only when it is linked to bovine serum albumin. A mechanism of contact quenching is proposed. Variables related to the terpene microextraction procedure were carefully studied, namely drop composition and volume, microextraction time, sample volume and temperature, stirring rate and salt addition. The only sample treatment is the dilution of cosmetic with 40% (v/v) ethanol. Citronellol was selected as a representative terpene for calibration purposes. According to the European legislation, the probability-concentration graph of the screening system was established using 0.001% (w/w) as the cut-off level. Low limits of detection with simple instrumentation, absence of matrix effects and high sample throughput can be emphasized.
Keywords: Screening; Terpenes; Cosmetics; Headspace single-drop microextraction; Fluorescein-BSA probe; Microvolume fluorospectrometry
Two-photon excitation with pico-second fluorescence lifetime imaging to detect nuclear association of flavanols by Irene Mueller-Harvey; Walter Feucht; Juergen Polster; Lucie Trnková; Pierre Burgos; Anthony W. Parker; Stanley W. Botchway (pp. 68-75).
Display Omitted► This fluorescence lifetime imaging microscopy (FLIM) technique for flavanols overcomes autofluorescence interference in cells. ► Plant flavanols differed in their lifetimes. ► Dissolved and bound flavanols revealed contrasting lifetime changes. ► This technique will allow studying of flavanol trafficking in live cells.Two-photon excitation enabled for the first time the observation and measurement of excited state fluorescence lifetimes from three flavanols in solution, which were ∼1.0ns for catechin and epicatechin, but <45ps for epigallocatechin gallate (EGCG). The shorter lifetime for EGCG is in line with a lower fluorescence quantum yield of 0.003 compared to catechin (0.015) and epicatechin (0.018). In vivo experiments with onion cells demonstrated that tryptophan and quercetin, which tend to be major contributors of background fluorescence in plant cells, have sufficiently low cross sections for two-photon excitation at 630nm and therefore do not interfere with detection of externally added or endogenous flavanols in Allium cepa or Taxus baccata cells. Applying two-photon excitation to flavanols enabled 3-D fluorescence lifetime imaging microscopy and showed that added EGCG penetrated the whole nucleus of onion cells. Interestingly, EGCG and catechin showed different lifetime behaviour when bound to the nucleus: EGCG lifetime increased from <45 to 200ps, whilst catechin lifetime decreased from 1.0ns to 500ps. Semi-quantitative measurements revealed that the relative ratios of EGCG concentrations in nucleoli associated vesicles: nucleus: cytoplasm were ca. 100:10:1.Solution experiments with catechin, epicatechin and histone proteins provided preliminary evidence, via the appearance of a second lifetime ( τ2=1.9–3.1ns), that both flavanols may be interacting with histone proteins. We conclude that there is significant nuclear absorption of flavanols. This advanced imaging using two-photon excitation and biophysical techniques described here will prove valuable for probing the intracellular trafficking and functions of flavanols, such as EGCG, which is the major flavanol of green tea.
Keywords: Fluorescence lifetime imaging microscopy; Flavanols; Epigallocatechin gallate; Nuclear association; Histone proteins; Multiphoton
Aptamer sensor for cocaine using minor groove binder based energy transfer by Jinwen Zhou; Amanda V. Ellis; Hilton Kobus; Nicolas H. Voelcker (pp. 76-81).
Display Omitted► Cocaine is detected using an optical aptamer sensor. ► Aptamer changed from a partial single-stranded DNA with a short hairpin to a double-stranded T-junction when exposed to cocaine. ► Report the presence of cocaine using minor groove binder based energy transfer (MBET). ► MBET is between Hoechst 33342 bound to double-stranded T-junction and aptamer tethered FITC.We report on an optical aptamer sensor for cocaine detection. The cocaine sensitive fluorescein isothiocyanate (FITC)-labeled aptamer underwent a conformational change from a partial single-stranded DNA with a short hairpin to a double-stranded T-junction in the presence of the target. The DNA minor groove binder Hoechst 33342 selectively bound to the double-stranded T-junction, bringing the dye within the Förster radius of FITC, and therefore initiating minor groove binder based energy transfer (MBET), and reporting on the presence of cocaine. The sensor showed a detection limit of 0.2μM. The sensor was also implemented on a carboxy-functionalized polydimethylsiloxane (PDMS) surface by covalently immobilizing DNA aptamers. The ability of surface-bound cocaine detection is crucial for the development of microfluidic sensors.
Keywords: Aptamer; Minor groove binder based energy transfer; Cocaine; Polydimethylsiloxane
Micellar electrokinetic chromatography-chemiluminescent detection of biogenic amines using N-(4-aminobutyl)- N-ethylisoluminol as derivatization reagent and trivalent copper chelate as chemiluminescence enhancer by Tao Li; Haoyue Xie; Zhifeng Fu (pp. 82-86).
Display Omitted► DPC was found to be an excellent enhancer for luminol-H2O2 CL system. ► Derivatization of biogenic amines was accomplished with a TEA-catalyzed method. ► A MEKC-CL method was established for highly sensitive detection of amino acids.A facile, sensitive and universal method was established for analysis of biogenic amines using micellar electrokinetic chromatography coupled with chemiluminescent (CL) detection. It was found that diperiodatocuprate (III) (K5[Cu(HIO6)2], DPC), a transition metal chelate at unstable high oxidation state, could effectively enhance the reaction between luminol-type compound and hydrogen peroxide, to produce very strong CL signal. In addition, triethylamine was found to be able to effectively improve the yield of the derivatization reaction between biogenic amines and a luminol-type derivatization reagent, N-(4-aminobutyl)- N-ethylisoluminol (ABEI). Based on these facts, three biogenic amines were pre-column derivatized with ABEI, and post-column detected using high sensitive luminol-hydrogen peroxide-DPC CL system. Since the background was quite low, and the signal was quite strong, a considerable improved sensitivity was obtained. The presented method had been successfully applied to simultaneously analyze glycine, proline and phenylalanine with the detection limits (S/N=3) of 0.030μmolL−1, 0.23μmolL−1 and 0.21μmolL−1, respectively. To evaluate its potential application value, glycine in saliva and urine samples was detected using this method, and satisfied results were obtained. This approach can be further extended to detection of many other compounds such as peptides and drugs by using luminol-type derivatization reagent.
Keywords: Micellar electrokinetic chromatography; Diperiodatocuprate (III); Chemiluminescence; N; -(4-Aminobutyl)-; N; -ethylisoluminol; Biogenic amines
An ultrafiltration high-performance liquid chromatography coupled with diode array detector and mass spectrometry approach for screening and characterising tyrosinase inhibitors from mulberry leaves by Zhenzhong Yang; Yufeng Zhang; Lijuan Sun; Yi Wang; Xiumei Gao; Yiyu Cheng (pp. 87-95).
Display Omitted► A new assay based on ultrafiltration HPLC–DAD–MS has been developed for rapid screening and identification of ligands for tyrosinase. ► Twelve compounds with tyrosinase binding activity were found from extract of mulberry leaves. ► Two malonyl-glycosylflavones were identified as new tyrosinase inhibitors.Tyrosinase is a key enzyme in melanin synthesis. Its inhibitor may be used to efficiently treat hyperpigmentation and widely applied in cosmetic products and food supplements. In the present study, a new assay based on ultrafiltration high-performance liquid chromatography coupled with diode array detector and mass spectrometry (HPLC–DAD–MS) was developed for the rapid screening and identification of ligands for tyrosinase. Experiments were carried out to select the optimal binding conditions, tyrosinase concentration, and incubation time. Non-specific binding to the denatured tyrosinase was also investigated. Twelve compounds with tyrosinase binding activity were found in mulberry leaf extracts. The identities of these compounds were characterised by HPLC–DAD–MS n. Particularly, two compounds, namely, quercetin-3-O-(6-O-malonyl)-β-d-glucopyranoside and kaempferol-3-O-(6-O-malonyl)-β-d-glucopyranoside, were identified as new tyrosinase inhibitors. The screening results were verified by tyrosinase inhibition assays. Experimental results proved that the proposed method could rapidly screen tyrosinase inhibitors in complex mixtures.
Keywords: Ultrafiltration; HPLC–DAD–MS; Morus alba; Tyrosinase inhibitor
Capillary electrochromatography–mass spectrometry determination of melamine and related triazine by-products using poly(divinyl benzene-alkene-vinylbenzyl trimethylammonium chloride) monolithic stationary phases by Hsi-Ya Huang; Cheng-Lan Lin; Shu-Huei Jiang; Brenda Singco; Yi-Jie Cheng (pp. 96-103).
Display Omitted► Detection of trace-amounts of melamine and its related by-products by CEC–UV or CEC–MS. ► Stationary phases used were a series of poly(divinyl benzene-alkene-vinylbenzyl trimethylammonium chloride) monoliths. ► Optimization of mobile phase compositions and MS parameters for melamine separation and detection. ► The optimized CEC method determined melamine contaminations in dairy products.In this study, a capillary electrochromatography (CEC) method coupled either with UV or mass spectrometric detection was developed for the detection of trace-amounts of melamine and its related by-products (ammeline, ammelide, and cyanuric acid). A series of poly(divinyl benzene-alkene-vinylbenzyl trimethylammonium chloride) monolithic columns, which were prepared by a simple in situ polymerization with divinyl benzene (DVB), vinylbenzyl trimethylammonium chloride (VBTA) and different types of alkene monomers such as 1-octene, 1-dodecene or 1-octadecene were used as separation columns, with the poly(DVB-1-dodecene-VBTA) monolith as the optimal chromatographic material because it provided a better separation. The detection limits of four melamine derivatives were in the ranged of 0.6–2.18mgL−1 by the optimal CEC–UV mode, and were reduced from 2.2 to 19.4μgL−1 by the optimal CEC–MS mode. Finally, the proposed CEC methods successfully determined melamine contaminations (0.1mgL−1 per analyte) in several dairy products as test samples with analyte recovery range of 69–85% (intra-day) and 68–75% (inter-day), and with peak area reproducibility range of 4.3–8.6% and 8.7–15.6% for intra-day and inter-day, respectively. This is the first report for CEC separation coupled with MS detection applied in trace melamine residue analyses with a faster separation and comparable or even better detection ability than previous GC–MS, CE–MS, as well as LC–MS methods.
Keywords: Capillary electrochromatography; Mass spectrometry; Melamine; Melamine derivatives