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Application of automated eightfold suppression of water and ethanol signals in H-1 NMR to provide sensitivity for analyzing alcoholic beverages

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Application of automated eightfold suppression of water and ethanol signals in H-1 NMR to provide sensitivity for analyzing alcoholic beverages

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Abstract

The 400 MHz (1)H NMR analysis of alcoholic beverages using standard pulse programs lacks the necessary sensitivity to detect minor constituents such as methanol, acetaldehyde or ethyl acetate. This study investigates the application of a shaped pulse sequence during the relaxation delay to suppress the eight (1)H NMR frequencies of water and ethanol (the OH singlet of both water and ethanol, as well as the CH(2) quartet and CH(3) triplet of ethanol). The sequence of reference measurement for frequency determination followed by the suppression experiment is controlled by a macro in the acquisition software so that a measurement under full automation is possible (12 min per sample total time). Additionally, sample preparation was optimized to avoid precipitation, which is facilitated by 1:1 dilution with ethanol and pH 7.4 buffer. Compared with the standard water presaturation pulse program, the eightfold suppression allowed a significantly higher setting of receiver gain without receiver overflow, which significantly increased the signal-to-noise ratio by an average factor of 10. The signal intensities increased by a factor of 20. The resulting limits of detection (below 1 g/hl of pure alcohol) now allow the control of legal requirements for minor compounds in alcoholic beverages.

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... The NOESYGPPS was designed by Bruker and described elsewhere. 25 The NOESYGPPS sequence was preferred herein, because it has been found to provide higher setting of receiver gain without receiver overow. 25 Furthermore, it has been reported to signicantly increase the signal-to-noise ratio by an average factor of 10. ...
... 25 The NOESYGPPS sequence was preferred herein, because it has been found to provide higher setting of receiver gain without receiver overow. 25 Furthermore, it has been reported to signicantly increase the signal-to-noise ratio by an average factor of 10. Signal intensities have been found to be increased by a factor of 20. ...
... The resulting limits of detection (below 1 g h L À1 (or 10 mg L À1 ) of pure alcohol) were a prerequisite for the control of legal requirements and for analyzing the minor compounds in alcoholic beverages. 25 The sequence essentially involved the application of a 25 Hz radiofrequency (RF) eld for presaturation. The phase and amplitude modulated rectangular shaped pulse was applied during relaxation delay (RD) with a frequency spectrum of eight individual bands (frequencies 1-8) to achieve simultaneous and highly selective suppression of the water singlet (frequency 1, RF-eld strength 25 Hz) and the seven individual lines of the ethanol quartet (frequency 2-5, RF-eld strength $ 4 Hz each) and triplet (frequency 6-8, RF-eld strength $ 4 Hz each) without affecting the rest of the spectral features. ...
Article
Shifted peak positions in 1H-Nuclear magnetic resonance (1H-NMR) spectroscopy of wine samples are inevitably occurring mainly due to variations in the sample matrix, which consists of ethanol, glycerol, carbohydrates, acids, phenolic compounds, minerals, and aroma compounds. Slight variations in pH during sample preparation or fluctuations in instrumental factors may contribute to shifted peak positions that need to be corrected before subjecting the NMR data to chemometric techniques to ensure samples are compared on the correct chemical shift scale. In the current work, a novel procedure for correcting 1H-NMR spectroscopy peak positions was developed by mapping of the raw NMR spectra on a common chemical shift axis using a simple interpolation approach. The mapping allowed a substantial correction of peak positions and subsequently reduced the computational burden in further spectral processing. Fine-tuning of the peak alignments was carried out efficiently by interval-wisely applying the correlation optimized warping (COW) algorithm. Our preceding mapping approach enabled the use of substantially simpler alignment parameters of the COW algorithm, thereby accelerating the whole peak alignment process. The developed procedure may also be suitable for facilitating NMR analyses of other sample types, such as agricultural, clinical or pharmaceutical samples in targeted or untargeted analytical approaches.
... Signal-to-noise calculation To quantitatively evaluate the enhancement in intensity (the amplitude of the highest peak in the signal region) and signal-to-noise ratio (SNR), the Bruker sino routine was applied to determine SNR [23]. The sino command in the TopSpin 3.2 software package gives the SNR of a 1D spectrum evaluated by the formula SNR = maxval/(2*noise), where maxval is the highest intensity in the spectral region and noise is the average level of noise in the noise region. ...
... The simplest solvent suppression (ZGPR in Bruker's standard library) uses a long continuous but weak intensity pulse that have same frequency with resonance frequency of water just before the main pulse (water presaturation). The method could suppress not only part of water signal, but also the proton exchange signal of OH, NH groups [23,24]. Therefore, the signal of formic acid was partially eliminated ( Fig. 1-(2)). ...
... The relationship between integrated peak areas and concentration showed good linearity with high correlation coefficient (R 2 value > 0.999) (Fig. 4a). The instrument detection method (IDL) and instrument quantification limit (IQL) of five compounds were calculated according to equations 2 and 3 base on signal-to-noise [23,25]. Results were given in Table 2. Methanol determination exhibited the most sensitivity with the lowest IDL and IQL of 0.02 mg/L and 0.07 mg/L respectively. ...
Conference Paper
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The 1H-NMR method for simultaneous quantification of methanol, ethanol and their metabolic products (formic acid and acetic acid) in human plasma was established. The effect of protein in plasma sample was removed by 25 % trichloroacetic acid (TCA) with the ratio of TCA and plasma sample at 1/5 (v/v). The small amount of D2O (estimated 1/10 v/v) was chosen due to the effect of water signal was eliminated by using the advance water suppression with NOESY pulse sequence. The different analytical parameters such as linearity, precision, accuracy, and specificity, limit of detection (LOD) and limit of quantification (LOQ) were validated. The method detection limit (MDL) of four compounds in blank plasma varied from 0.68 (for methanol) to 2.88 mg/L (for formic acids). The average recoveries of concentration in dynamic ranges were found to be 96 to 105%. The good linearity between concentration calculated by integrated signal and measured obtained by calibration curves confirmed that concentration of analytes in plasma can be directly determined from the 1H-NMR signal. The proposed method has been successfully applied for direct determination of five compounds in 9 patient’s plasma samples with the satisfactory results compared to GC/FID method. The analytical procedure can be useful for diagnosis and evaluation of treatment of methanol poisoning in Vietnamese hospitals.
... The technique has gained popularity in the screening of beverages for components for authentication purposes 3 , as well as routine analysis and rapid detection of potentially unsafe substances [4][5][6][7] . As a result of the minimal sample preparation and the short analysis time, the sample output is considerably increased compared to other approaches 1,[8][9][10] . The consumption of surrogate alcohol, a subgroup of unrecorded alcohol, continues to endanger public health in Russia 11 , mainly because of high ethanol content and lower prices compared to recorded alcohol. ...
... A suppression of eight frequencies (around 4.70 ppm for OH-group signal for both water and ethanol, 3.66 ppm for ethanol CH 2 quartet, and 1.18 ppm for the corresponding ethanol CH 3 triplet) was conducted. The measurement protocol was previously described in detail 8,9 . All 1 H-NMR spectra were automatically phase and baseline corrected using the Topspin 3.2 software package (Bruker BioSpin, Rheinstetten, Germany). ...
Article
Nuclear magnetic resonance (NMR) spectroscopy was applied to the analysis of alcoholic products in the context of health and safety control. A total of 86 samples of unrecorded alcohol were collected in Novosibirsk and nearby cities in Russia. Sampling was based on interviews with alcohol dependent patients, and unrecorded alcohol thus defined included illegally or informally produced alcoholic products (e.g., counterfeit or home-made alcoholic beverages) or surrogate alcohol in the form of cosmetic or medicinal products and industrial non-beverage alcohol such as antifreeze (antifreeze windshield washer fluid). For sample preparation, addition of buffer and of a water/ethanol mixture was required as single step. To detect potentially harmful samples, a nontargeted approach based on principal component analysis (PCA) was applied. The PCA scores plot shows six conspicuous samples with highly divergent scores from the rest. These samples are antifreeze windshield washer fluids containing high amounts of methanol, with concentrations in a range between 7% and 48% vol. The antifreeze products were bought in regular retail sale and were claimed as “not containing methanol” on five out of six labels. Additionally, formic acid (1.1%) was observed in four of the alcohol-containing medicinal products. The major advantage of NMR over conventional methods is the fact that it not only provides the same quantitative data for specific compounds, but also allows rapid nontargeted screening for unknown contaminants.
... Occurrence data on furfuryl alcohol and β-myrcene were searched in the following databases: Additional data on the occurrence of furfuryl alcohol was also obtained from in-house analysis of 30 coffee (roasted coffee as beans, powder, or pods), 15 bread, 20 wine, and 50 alcoholic spirit samples (whiskey, brandy, and rum) submitted to our laboratory in the context of official control using nuclear magnetic resonance spectroscopy (NMR) [27]. For this, spectra previously acquired for other purposes were re-quantified for furfuryl alcohol. ...
... (Mestrelab Research, Santiago de Compostela, Spain) [29]. For evaluation of spirits, the NMR method of Monakhova et al. [27] was applied. The NMR methods achieved a limit of detection (LOD) of 3.2 mg/L and limit of quantification (LOQ) of 8.6 mg/L. ...
Article
Full-text available
For decades, compounds present in foods and beverages have been implicated in the etiology of human cancers. The World Health Organization (WHO) International Agency for Research on Cancer (IARC) continues to classify such agents regarding their potential carcinogenicity in humans based on new evidence from animal and human studies. Furfuryl alcohol and β-myrcene are potential human carcinogens due to be evaluated. The major source of furfuryl alcohol in foods is thermal processing and ageing of alcoholic beverages, while β-myrcene occurs naturally as a constituent of the essential oils of plants such as hops, lemongrass, and derived products. This study aimed to summarize the occurrence of furfuryl alcohol and β-myrcene in foods and beverages using literature review data. Additionally, results of furfuryl alcohol occurrence from our own nuclear magnetic resonance (NMR) analysis are included. The highest content of furfuryl alcohol was found in coffee beans (>100 mg/kg) and in some fish products (about 10 mg/kg), while among beverages, wines contained between 1 and 10 mg/L, with 8 mg/L in pineapple juice. The content of β-myrcene was highest in hops. In conclusion, the data about the occurrence of the two agents is currently judged as insufficient for exposure and risk assessment. The results of this study point out the food and beverage groups that may be considered for future monitoring of furfuryl alcohol and β-myrcene.
... Nuclear magnetic resonance (NMR) spectroscopy was used to monitor the carbonyl and acetal-type compounds in situ. NMR spectra collection was performed as described by Monakhova et al. (2011). A Bruker 700 Ultrashield (5 mm TXI 700 MHz Z-Gradient) was used to monitor the carbonyl and acetal-type compounds in vodka. ...
... A Bruker 700 Ultrashield (5 mm TXI 700 MHz Z-Gradient) was used to monitor the carbonyl and acetal-type compounds in vodka. NMR spectra collection was performed based on a method previously described by Monakhova et al. (2011) that involved a solvent signal suppression program of ethanol and water spectra. Samples at two different pH values were analyzed using two different buffer systems. ...
... During the last few years, NMR-based metabolomics, especially 1 H NMR acquisition, has played a principal role in the characterization of complex food matrices, and it has been largely used in metabolomic studies of foodstuffs, allowing geographical discrimination as well as its quality and authentication assessment (Fortunato, Rocha, & Sheen, 2018). NMR-based metabolomics has been used to classify different types of matrices, such as beer (da Silva, Flumignan, Tininis, Pezza, & Pezza, 2019), whiskey (Monakhova et al., 2011), grape marc spirits (Fotakis & Zervou, 2016) and wine (Gougeon et al., 2018). Although previous metabolomics studies for golden rums have been reported by LC coupled to mass spectrometry (LC-MS) (Belmonte-Sánchez, Romero-González, Arrebola, Vidal, & Garrido Frenich, 2019) and gas chromatography coupled to MS (GC-MS) (Belmonte-Sánchez et al., 2018), up to our knowledge, NMR-based untargeted metabolomics has never been applied for golden rums comparison. ...
... The implementation of chemometric methods combined with the potentiality of NMR spectroscopy allows for obtaining comprehensive fingerprints and therefore, it can be used in metabolomics researches. 1 H NMR experiment (1 dimensional nuclear Over-hauser effect spectroscopy (NOESY)) with water and ethanol suppression followed by multivariate analysis is a powerful tool for the discrimination of alcoholic beverages and for their quality control (Longobardi et al., 2017;Monakhova et al., 2011). In matrices with high content of major components (as ethanol in rums), the 13 C satellite signals suppression is also important to obtain an adequate dynamic range, which allows the correct acquisition of low-concentration metabolites (Bharti & Roy, 2012). ...
Article
1H NMR spectroscopy combined with chemometrics was applied for the first time for golden rum classification based on several factors as fermentation barrel, raw material, distillation method and aging. Principal component analysis (PCA) was used to assess the overall structure, and partial least square discriminant analysis (PLS-DA) was carried out for the analytical discrimination of rums. Additionally, data-fusion of 1H NMR and chromatographic techniques (gas and liquid chromatography) coupled to mass spectrometry was applied to provide more accurate knowledge about rums. This approach provided a classification of samples with lower error rate than the one obtained by the use of a single technique (spectroscopic or chromatographic). The results showed that 1H NMR spectroscopy is an appropriate technique for the suitable classification of >95.5% of the samples. When data fusion methodology of spectroscopic and spectrometric data was performed, the prediction efficiency can reach 100% of the samples.
... The spectra were automatically acquired at 300.0 K under the control of ICON-NMR (Bruker BioSpin, Rheinstetten, Germany). The measurement protocol was previously described in detail (Monakhova, Kuballa, & Lachenmeier, 2012;Monakhova et al., 2011). All 1 H NMR spectra were automatically phased and baseline corrected using the Topspin 3.0 software package (BrukerBioSpin, Rheinstetten, Germany). ...
Article
Samples of unrecorded opaque beers (n=58; 40 based on maize, 5 on sorghum and 13 on other plants) and recorded wines (n=8) in Kenya were screened for aflatoxins using a rapid ELISA technique followed by confirmation using liquid chromatography-tandem mass spectrometry. Six of the maize beers were obtained from Kibera slums in Nairobi County. Aflatoxin contamination was detected in six unrecorded beers (10%), but in none of the recorded wines. Remarkably, three of the aflatoxin positive samples were from the Kibera slums.
... However, pH adjustment and/or buffer addition are usually performed to minimize the signal shifts in the NMR spectra due to pH fluctuations amongst different wine samples [28]. Lyophilization and multiple solvent suppression can be used to remove the strong and dominating signals of water and ethanol [29,30]. When performing targeted NMR analysis, for example of phenolic compounds, metabolites extraction must be carried out [31,32]. ...
Article
Full-text available
This study investigates the metabolome of 26 experimental cool-climate wines made from 22 grape varieties using two different protocols for wine analysis by proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The wine samples were analyzed as-is (wet) and as dried samples. The NMR datasets were preprocessed by alignment and mean centering. No normalization or scaling was performed. The "wet" method preserved the inherent properties of the samples and provided a fast and effective overview of the molecular composition of the wines. The "dried" method yielded a slightly better sensitivity towards a broader range of the compounds present in wines. A total of 27 metabolites including amino acids, organic acids, sugars, and alkaloids were identified in the ¹H-NMR spectra of the wine samples. Principal component analysis was performed on both NMR datasets evidencing well-defined molecular fingerprints for 'Baco Noir', 'Bolero', 'Cabernet Cantor', 'Cabernet Cortis', 'Don Muscat', 'Eszter', 'Golubok', 'New York Muscat', 'Regent', 'Rondo', 'Triomphe d'Alsace', 'Précose Noir', and 'Vinoslivy' wines. Amongst the identified metabolites, lactic acid, succinic acid, acetic acid, gallic acid, glycerol, and methanol were found to drive sample groupings. The ¹H-NMR data was compared to the absolute concentration values obtained from a reference Fourier transform infrared method, evidencing a high correlation.
... The acquisition of data has also made tremendous progress during the last decade. Signal suppression of water, and more recently other major solvents has become routine (e. g. ethanol) ( Duarte et al., 2002;Monakhova et al., 2011) and the repeatability and re- producibility (Minoja & Napoli, 2014) is improved, setting the pre- requisite for databanks of spectral information. After data acquisition a procedure that is called binning or bucketing is often performed, whereby small chemical shift regions (bins or buckets, e.g. ...
Article
Background: The authenticity of foodstuffs and associated fraud has become an important area. It is estimated that global food fraud costs approximately $US49b annually. In relation to testing for this malpractice, analytical technologies exist to detect fraud but are usually expensive and lab based. However, recently there has been a move towards non-targeted methods as means for detecting food fraud but the question arises if these techniques will ever be accepted as routine. Scope and approach: In this opinion paper, many aspects relating to the role of non-targeted spectroscopy based methods for food fraud detection are considered: (i) a review of the current non-targeted spectroscopic methods to include the general differences with targeted techniques; (ii) overview of in-house validation procedures including samples, data processing and chemometric techniques with a view to recommending a harmonized procedure; (iii) quality assessments including QC samples, ring trials and reference materials; (iv) use of “big data” including recording, validation, sharing and joint usage of databases. Key findings and conclusions: In order to keep pace with those who perpetrate food fraud there is clearly a need for robust and reliable non-targeted methods that are available to many stakeholders. Key challenges faced by the research and routine testing communities include: a lack of guidelines and legislation governing both the development and validation of non-targeted methodologies, no common definition of terms, difficulty in obtaining authentic samples with full traceability for model building; the lack of a single chemometric modelling software that offers all the algorithms required by developers.
... The signals for ethanol (1.17 and 3.65 ppm), residual water (4.76 ppm), and the TSP chemical shift reference (0.00 ppm) are indicated. The small variations observed in the chemical shifts could be caused by pH differences or intermolecular interactions between the chemical compounds contained in the beer (Liu, Dong, Yin, Li, & Gu, 2012;Monakhova et al., 2011), as can be seen for the 2.04, 2.35, and 2.57 ppm signals corresponding to acetic, pyruvic, and succinic acids, respectively. This causes small spectral misalignment. ...
... The presaturation power and the 90° pulse length were optimized for each sample. Wine NMR spectra were recorded following the procedure described elsewhere (Cassino et al., 2017;Godelmann et al., 2013;Monakhova et al., 2011). Choline (3.18 (s, N-CH 3 ), 4.05 (m, C2H 2 )) was quantified comparing the signal area of the singlet at 3.18 ppm with that of a standard choline sample following the same procedure pre- viously reported (Cassino et al., 2017). ...
Article
The study of wine evolution during bottle aging is an important aspect of wine quality. Ten different red wines (Vitis vinifera) from Piedmont region were analysed 3 months after bottling and after a further 48 month conservation in a climate controlled wine cellar kept at a constant/controlled temperature of 12 °C. Two white wines (Vitis vinifera) were included in this study for comparison purposes. White wines were analysed 3 months after bottling and after further 24 months of bottle aging in the same climate controlled wine cellar. Metabolite changes during this period were evaluated using ¹H NMR spectroscopy combined with statistical analysis. Metabolite variations due to wine aging were minimal compared to those that resulted from a different wine type and wine geographical origin. Therefore, it was necessary to remove this source of variability to discriminate between fresh and refined samples. The storage at low and controlled temperature for 2 or 4 years permitted a slow but progressive evolution of all wines under investigation. 1H NMR spectroscopy, implemented with statistical data analysis, allowed identifying and differentiating wine samples from the two aging stages. In most wines, a decrease in organic acids (lactic acid, succinic acid and tartaric acid) and an increase in esters (ethyl acetate and ethyl lactate) was observed. Catechin and epicatechin decreased during aging in all wines while gallic acid increased in almost all red wines.
... DL: There was another interesting question: is it possible to enhance a signal intensity of one component in a multi component mixture? It's not quite clear but I think the question goes in this way that you want to only quantify this one single signal and perhaps suppress the other signals like, we are doing with the alcohol suppression of several signals to improve the detectability of the other minor compounds 23,24 . MS: What you could do is a selective excitation, for example. ...
Article
Full-text available
During the XIII International Conference on the Applications of Magnetic Resonance in Food Science, which was held in Karlsruhe, Germany, from 7th to 10th of June 2016, a discussion session entitled “Quantitative nuclear magnetic resonance (qNMR)” was organized. The conference participants had the opportunity to submit written questions as well as to ask ad-hoc questions during the session, which were to be answered by a panel of qNMR experts from several application fields. This article provides an edited and referenced transcript of the session. The major topics were centred on instrumental requirements for qNMR, and the participants were in agreement that modern digital NMR spectrometers guarantee a long-term stability of measurements and calibrations, sometimes over several years. However, the panel also agreed that method validation is an absolute necessity in qNMR as in every other field of quantitative analytical chemistry. Validation strategies may depend on the purpose of the method and vary between multi-component analyses of foods and beverages, compared to single target assays e.g. in verification of reference standards. Approaches to establish limits of detection and to ensure the required method accuracy were suggested. The discussion was closed with a general agreement of the experts that qNMR in food science will gain a wider application range in the future. The necessity to abolish regulatory hindrances – including the approval of using qNMR in reference methods – was stressed.
... In addition, a 2D fast J-resolved data set was recorded (jresgpprqf). Experimental parameters were taken from the Bruker standard data sets for SGF-Juice-Profiling™ (Monakhova et al., 2011;Spraul et al., 2009) except for the number of scans, which was adjusted to 32. The excitation pulse was determined automatically before each measurement. ...
Article
Within the cocoa market (Theobroma cacao L.), quality and prices are often determined by geographical origin, making traceability indispensable. Therefore, to investigate possibilities of tracing by analytical methods, 48 carefully selected cocoa samples from 20 countries have been profiled using a combination of stable isotope-ratio mass spectrometry (IRMS) and proton nuclear magnetic resonance (1H NMR). Chemometric analysis of combined data sets from both, stable isotope data (δ13C, δ15N, δ18O, δ2H, %C, %N, %O, %H) and 1H NMR fingerprints, achieved good separation with increased classification rates compared to classification with data of the isolated methods. IRMS contributed primarily to discrimination between countries, while 1H NMR significantly contributed to separation of varieties, but also the regions within individual countries. This study thus demonstrates that combination of two analytical methods is an effective tool to enhance both, accuracy and precision, in authenticity testing of cocoa.
... Nuclear magnetic resonance spectroscopy in combination with chemometrics has been applied either for routine quality control and/or detection of potentially harmful substances in beverages such alcohol [20], fruit juices [21,22] and coffee [8,23]. NMR spectroscopy may be applied for the quantification of caffeine, OMC, kahweol, 5-hydroxymethylfurfural (HMF) and furfuryl alcohol in coffee [24][25][26]. ...
Preprint
Full-text available
Monitoring coffee quality as a means of detecting and preventing economically motivated fraud is an important aspect of international commerce today. Therefore, there is a compelling need for rapid high throughput validated analytical techniques such as quantitative proton NMR spectroscopy for screening and authenticity testing. For this reason, we sought to validate an NMR spectroscopic method for routine screening of coffee for quality and authenticity. A factorial experimental design was used to investigate the influence of NMR device, extraction time and nature of coffee on the content of caffeine, 16-O-methylcafestol (OMC), kahweol, furfuryl alcohol and 5-hydroxymethylfurfural (HMF) in coffee. The method was successfully validated for specificity, selectivity, sensitivity and linearity of detector response. The proposed method produced satisfactory precision for all analytes in roasted coffee, except for kahweol in canephora (robusta) coffee. The proposed validated method may be used for routine screening of roasted coffee for quality and authenticity control, as its applicability was demonstrated during the recent OPSON VIII Europol-Interpol operation on coffee fraud control.
... Nuclear magnetic resonance spectroscopy in combination with chemometrics has been applied either for routine quality control and/or detection of potentially harmful substances in beverages such as alcohol [20], fruit juices [21,22] and coffee [8,23]. NMR spectroscopy may be applied for the quantification of caffeine, OMC, kahweol, 5-hydroxymethylfurfural (HMF) and furfuryl alcohol in coffee [24][25][26]. ...
Article
Full-text available
Monitoring coffee quality as a means of detecting and preventing economically motivated fraud is an important aspect of international commerce today. Therefore, there is a compelling need for rapid high throughput validated analytical techniques such as quantitative proton nuclear magnetic resonance (NMR) spectroscopy for screening and authenticity testing. For this reason, we sought to validate an 1H NMR spectroscopic method for the routine screening of coffee for quality and authenticity. A factorial experimental design was used to investigate the influence of the NMR device, extraction time, and nature of coffee on the content of caffeine, 16-O-methylcafestol (OMC), kahweol, furfuryl alcohol, and 5-hydroxymethylfurfural (HMF) in coffee. The method was successfully validated for specificity, selectivity, sensitivity, and linearity of detector response. The proposed method produced satisfactory precision for all analytes in roasted coffee, except for kahweol in canephora (robusta) coffee. The proposed validated method may be used for routine screening of roasted coffee for quality and authenticity control (i.e., arabica/robusta discrimination), as its applicability was demonstrated during the recent OPSON VIII Europol-Interpol operation on coffee fraud control.
... CC BY 4.0 License. of these techniques and consists in the application during the relaxation delay of a low power radiofrequency (RF) field on resonance with the solvent signal (Hoult, 1976) (Ross et al., 2007). 25 Multiple solvent signal suppression is a necessity in LC-NMR and for the study of alcoholic beverages by 1 H NMR. In the latter case, the eight signals produced by water and ethanol can be efficiently attenuated (Monakhova et al., 2011). However, the presence of solvents is not a problem in 13 C NMR spectroscopy since their resonance lines are very sharp, relatively to the width of the observation frequency window, and are not likely to overlap those of interest. ...
Preprint
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Abstract. The analysis by proton-decoupled carbon-13 nuclear magnetic resonance spectroscopy of samples dissolved in solvents presenting strong multiple resonances can be facilitated by the suppression of these resonances by multi–site presaturation. The advantage drawn from this operation is the elimination of the possible artifacts that arise from the solvent signals in non–optimized decoupling conditions. Solvent presaturation was implemented on glycerol, 1,2–propanediol, 1,3–propanediol, 1,2–butanediol, 1,3–butanediol with at least 94 % on–resonance efficiency and a bandwidth of less 5 than 50 Hz measured at 50 % signal intensity decrease. The experimental measurement of the signal suppression bandwidth leads to unexpected selectivity profiles for frequency close resonances. Computer resolution of the Bloch equations during multi–site presaturation provide an insight into the origin of the observed profile perturbations.
... The most important step of the NMR analysis is to characterise the minor compo nents whose signals can be several orders of magnitude lower than the major ones. Elimination of major signals is very important in case of wines, where the water and ethanol are the main compounds (Monakhova et al. 2011). ...
Chapter
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Grapevine is one of the most cultivated fruit crops worldwide, which reflects its great economy significance. Due to its extensive exploitation for wine production and because of the beneficial health effects of grape metabolites, grapevine got into the spotlight of science and has become a model woody species in plant biotechnology. As a result, few years ago the grapevine genome was fully sequenced, presenting a molecular basis for further studies. In vitro propagation techniques and genetic markers have boosted the development of grape breeding in a dynamic industry with a focus on creating cultivars with improved metabolite profile, enhanced tolerance to pathogens and better adaptation to wide ecological factors. The final touch of grape biotechnology is made by metabolomic analyses, which estimate the efficiency of genome improvement and the influence of environmental factors and enological practises on grape and wine quality.
... The suppression methods are derived in these two cases from the original excitation sculpting pulse sequence (Hwang and Shaka, 1995). The eight signals produced by water and ethanol can be efficiently attenuated by presaturation for the study of alcoholic beverages by 1 H NMR (Monakhova et al., 2011). However, the presence of solvents is not a problem in 13 C NMR spectroscopy since their resonance lines are very sharp, relative to the width of the observation frequency window, and are not likely to overlap those of interest. ...
Article
Full-text available
The analysis by proton-decoupled carbon-13 nuclear magnetic resonance spectroscopy of samples dissolved in solvents presenting strong multiple resonances can be facilitated by the suppression of these resonances by multisite presaturation. The advantage drawn from this operation is the elimination of the possible artifacts that arise from the solvent signals in non-optimized decoupling conditions. Solvent presaturation was implemented on glycerol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, and 1,3-butanediol with at least 94 % on-resonance efficiency and a bandwidth of less than 50 Hz measured at 50 % signal intensity decrease. The experimental measurement of the signal suppression bandwidth leads to unexpected selectivity profiles for close-frequency resonances. Computer resolution of the Bloch equations during multisite presaturation provide an insight into the origin of the observed profile perturbations.
... This is necessary to accommodate sample specific shifts of the respective resonances that could lead to variations in signal suppression efficiency. Such intersample variations of the chemical shifts of ethanol protons are described in the literature to depend on pH variations or on some kind of unknown interactions in the particular samples [11]. Since this does not seem to be a satisfying explanation, we wondered if the variations could indeed account for differing ethanol sample concentrations. ...
Article
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Craft breweries that tend to convince consumers with new interpretations of (ancient) beer styles increasingly influence the traditional beer market. Thereby, also ingredients not directly compliant with German beer purity laws come into use. Official food control currently faces the general problem of verifying food authenticity based on instrumental analytical methods. Related tasks in this field are the detection of non-labelled ingredients and the verification of product claims such as special food processing methods. For that purpose, chemometric analysis of high-resolution 1H NMR spectra was applied for the differentiation of related beer styles including also special beers. It could be shown that pilsner style beers, wheat beers, India pale ales, sour beers, and special beers can be easily differentiated applying consecutive principal component analysis. Thereby, it turned out that crafted pilsner style beers are distinguishable from industrial pilsner style beers based on their organic acid profiles. Furthermore, three conspicuous compounds present in two different batches of only one of the beer samples were identified as allyl alcohol, 1,3-propanediol, and 3-hydroxypropionic acid directly from the NMR spectra without any further analytical efforts. Finally, the present paper serves as a proof of concept that NMR-based quantification is also possible using chemical shift information instead of signal intensities/integrals—at least in special cases.
... In other instances, the solvent signal suppression during the analysis is the proposed alternative to avoid complex, time-consuming, and costly sample preparation procedures. This approach has been successfully applied to the determination of methanol in spirits (Monakhova et al. 2011). ...
... If suppression pulse sequences have to be used to suppress one or multiple resonances (e.g., water and ethanol for alcoholic beverages), it has to be checked that the utilized suppression scheme does not affect signals located closely to the suppressed region (offset-dependent factor 1/F is equal for the whole data set) [4]. ...
Technical Report
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In the first part of the NMR technical report (see Guide to NMR Method Development and Validation – Part I: Identification and Quantification), the special criteria to facilitate development of NMR-based applications is described. These guidelines (Part I) mostly deal with general requirements, such as NMR spectra acquisition, identification, developing and validation of univariate quantification methods. However, the traditional univariate approach for quantification does not work in case of considerable spectral overlap. Consequently, a range of alternative approaches based on multivariate data treatment (chemometrics) have been appeared and the number of their practical applications for NMR data sets is constantly increasing. This report provides guidelines for the proper use of chemometrics in NMR analysis, considering NMR spectral pre-processing and discussing some specific requirements separately for multivariate classification and multivariate calibration.
... al of Drug Policy 32 (2016) 1-2 Table 1 Results of ISO 4120 sensory analysis using triangle testing for differentiation of alcohol-free from alcohol-containing spirits. The alcoholic strength of all alcohol-free products was confirmed as being less than 2 g/l (the maximum limit for alcohol-free beverages in Germany) using NMR analysis according to Monakhova et al. (2011). b According to ISO 4120 (2004). The a-risk level is stated for the trials with significant differentiation (*a = 0.001). ...
Article
The reduction of the potency of alcoholic products without compromising consumer preferences has been suggested as possibility to decrease alcohol-related harms. There is some evidence that a large percentage of the population may not be able to differentiate between different strengths of alcohol such as spirits with differences of less than 10% vol. As novelty product, alcohol-free spirits were introduced into the market with claims that they would be indistinguishable from normal spirits. By testing three products using ISO 4120 methodology, these claims could not be verified as the products were significantly different and the test panel was able to correctly assign the alcoholic strength. The taste of ethanol apparently cannot be simulated with the current technology. From a public health point of view, it would thus be more promising to offer alcohol-reduced spirits rather than alcohol-free spirits. Taxation by pure alcohol content could relatively favour this segment of the alcohol market.
... Multiple signal suppression, in which the water, ethanol methylene, and methyl group signals are suppressed eightfold, was introduced by Monakhova et al. (2011). This results in significant signal enhancement of the minor components. ...
Article
Wine authentication is vital in identifying malpractice and fraud, and various physical and chemical analytical techniques have been employed for this purpose. Besides wet chemistry, these include chromatography, isotopic ratio mass spectrometry, optical spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy, which have been applied in recent years in combination with chemometric approaches. For many years, ²H NMR spectroscopy was the method of choice and achieved official recognition in the detection of sugar addition to grape products. Recently, ¹H NMR spectroscopy, a simpler and faster method (in terms of sample preparation), has gathered more and more attention in wine analysis, even if it still lacks official recognition. This technique makes targeted quantitative determination of wine ingredients and nontargeted detection of the metabolomic fingerprint of a wine sample possible. This review summarizes the possibilities and limitations of ¹H NMR spectroscopy in analytical wine authentication, by reviewing its applications as reported in the literature. Examples of commercial and open‐source solutions combining NMR spectroscopy and chemometrics are also examined herein, together with its opportunities of becoming an official method.
... Thanks to the improved sensitivity and resolution of modern NMR spectrometers, a large number of wine components are detected simultaneously, which results in highly complex spectra and significant peak overlaps. The latter can be somewhat evaded by the use of solvent suppression techniques, such as WET (water suppression enhanced through T 1 effects), WATERGATE, and NOESY (Nuclear Overhauser effect NMR spectroscopy) presaturation sequences [58,59]. A serious drawback of NMR in food analysis is represented by the fact that tuning and resolution can be significantly altered between acquisitions, which may affect the intensity of all peaks in the spectra. ...
Article
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NMR is a swift and highly reproducible spectrometric technique that makes it possible to obtain spectra containing a lot of information about the sample analyzed. This approach helps major components be described in complex mixtures such as wine in just one analysis. Analysis of wine metabolites is very often used to understand the impact of geographical origin or variety on wine quality. NMR is often used for tracing the geographical origin of wine. Research on NMR metabolic effects of geographical origin is of great importance as the high added value of wines results from compliance with state legislation on the protected denomination of origin (PDO) and protected geographical indication (PGI) for the administration of the appellation of wines. A review of NMR with emphasis on SNIF-NMR in the analysis of wine authenticity is given. SNIF-NMR remains a method of choice for the detection of wine chaptalization as it is the only approach which provides position-specific information on the origin of sugar in wine. However, the sample preparation step, which lacks major improvements since its conception, is strenuous and expensive, and suffers from drawbacks in terms of low sample throughput. Mainstream 1D and 2D NMR experiments provide a fast and affordable way to authenticate wine based on the geographical origin, vintage, and variety discrimination, and include a simple and non-destructive sample preparation step. With this approach, spectral data processing often represents a crucial step of the analysis. With properly performed NMR experiments good to excellent differentiation of wines from different vintages, regions, and varieties was achieved recently.
... NMR spectroscopy is known to be a primary quantitative analytical technique with broad linear ranges (5 to 6 orders of magnitude) and has become of interest in the analysis of beverages such as wine. Multiple suppression of water and ethanol can significantly increase the sensitivity of matrixes containing water and ethanol (such as wine) during measurement in automated mode (5). In only one sample run, various ingredients of wine could be identified and quantified with specific signals. ...
Article
To examine whether NMR analysis is a suitable method for the quantitative determination of wine components, an international collaborative trial was organized to evaluate the method according to the international regulations and guidelines of the German Institute for Standardization/ International Organization for Standardization, AOAC INTERNATIONAL, the International Union of Pure and Applied Chemistry, and the International Organization of Vine and Wine. Sugars such as glucose; acids such as malic, acetic, fumaric, and shikimic acids (the latter two as minor components); and sorbic acid, a preservative, were selected for the exemplary quantitative determination of substances in wine. Selection criteria for the examination of sample material included different NMR spectral signal types (singlet and multiplet), as well as the suitability of the proposed substances for manual integration at different levels of challenge (e.g., interference as a result of the necessary suppression of a water signal or the coverage of different typical wine concentration ranges for a selection of major components, minor components, and additives). To show that this method can be universally applied, NMR measurement and the method of evaluation were not strictly elucidated. Fifteen international laboratories participated in the collaborative trial and determined six parameters in 10 samples. The values, in particular the reproducibility SD (SR), were compared with the expected Horwitz SD (SH) by forming the quotient SR/SH (i.e., the HorRat value). The resulting HorRat values of most parameters were predominantly between 0.6 and 1.5, and thus of an acceptable range.
... This screener should be able to achieve insights into the quantitative composition of spirit drinks, with little manual intervention, meaning that spectra processing and evaluation need to be fully automatic, similar to the screening method already developed for alcohol-free beverages [19]. The NMR sample preparation and measurement protocol is based on previous research [20,21]. This study only deals with quantitative analysis, while non-targeted analysis, e.g., for brand assignment, has been described elsewhere [21]. ...
Article
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Due to legal regulations, the rise of globalised (online) commerce and the need for public health protection, the analysis of spirit drinks (alcoholic beverages >15% vol) is a task with growing importance for governmental and commercial laboratories. In this article a newly developed method using nuclear magnetic resonance (NMR) spectroscopy for the simultaneous determination of 15 substances relevant to assessing the quality and authenticity of spirit drinks is described. The new method starts with a simple and rapid sample preparation and does not need an internal standard. For each sample, a group of 1 H-NMR spectra is recorded, among them a two-dimensional spectrum for analyte identification and one-dimensional spectra with suppression of solvent signals for quantification. Using the Pulse Length Based Concentration Determination (PULCON) method, concentrations are calculated from curve fits of the characteristic signals for each analyte. The optimisation of the spectra, their evaluation and the transfer of the results are done fully automatically. Glucose, fructose, sucrose, acetic acid, citric acid, formic acid, ethyl acetate, ethyl lactate, acetaldehyde, methanol, n-propanol, isobutanol, isopentanol, 2-phenylethanol and 5-(hydroxymethyl)furfural (HMF) can be quantified with an overall accuracy better than 8%. This new NMR-based targeted quantification method enables the simultaneous and efficient quantification of relevant spirit drinks ingredients in their typical concentration ranges in one process with good accuracy. It has proven to be a reliable method for all kinds of spirit drinks in routine food control.
... This screener should be able to get insight into the quantitative composition of spirits with little manual intervention, meaning that spectra processing and evaluation need to be fully automatic, similar to the screening method already developed for alcohol-free beverages [19]. The NMR sample preparation and measurement protocol is based on previous research [20,21]. This study only deals with quantitative analysis, while non-targeted analysis, e.g. for brand assignment, has been described elsewhere [21]. ...
Preprint
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Due to legal regulations, the rise of globalised (online) commerce and the need for public health protection, the analysis of spirits (alcoholic beverages > 15 % vol) is a task with growing importance for governmental and commercial laboratories. In this article a newly developed method using nuclear magnetic resonance (NMR) spectroscopy for the simultaneous determination of 15 substances relevant for the quality and authenticity assessment of spirits is described. The new method starts with a simple and rapid sample preparation and does not need an internal standard. For each sample a group of 1H-NMR spectra is recorded, among them a 2D spectrum for analyte identification and 1D spectra with suppression of solvent signals for quantification. Using the Pulse Length Based Concentration Determination (PULCON) method, concentrations are calculated from curve fits of the characteristic signals for each analyte. The optimisation of the spectra, their evaluation and the transfer of the results are done fully automatically. Glucose, fructose, sucrose, acetic acid, citric acid, formic acid, ethyl acetate, ethyl lactate, acetaldehyde, ethanol, methanol, n-propanol, isobutanol, isopentanol, 2-phenylethanol and 5-(hydroxymethyl)furfural (HMF) can be quantified with an overall accuracy better than 8 %. This new NMR-based targeted quantification method enables the simultaneous and efficient quantification of relevant spirits ingredients in their typical concentration ranges in one process with good accuracy. It has proven to be a reliable method for all kinds of spirits in routine food control.
Article
As wine oxidizes, ethanol is converted to acetaldehyde, but its accumulation is not predictable, due to poorly characterized reactions with alcohols, SO2, thiols, flavanols, and others. Measurement of these components has been thwarted by equilibria into the other forms during sample preparation. NMR spectra can be taken on intact samples and is thus ideal for this situation. Equilibria of acetaldehyde with glycerol, (+)-catechin, and glutathione were studied separately in model wine solutions at pH 3-4 by (1)H NMR and 2D ((1)H-(1)H) COSY spectra. Glycerol acetals had equilibrium constants between 1.14 ± 0.056 and 2.53 ± 0.043 M(-1), whereas ethylidene-bridged (+)-catechin dimers and glutathione thiohemiacetals had more favorable equilibria: from (3.92 ± 0.13) × 10(3) to (6.13 ± 0.32) × 10(3) M(-2) and from 10.18 ± 0.22 to 11.17 ± 0.47 M(-1), respectively. These data can be used to create accurate measures of acetaldehyde in its various forms and, consequently, offer insight into wine oxidation.
Chapter
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This chapter discusses methods for the detection and confirmation of the adulteration of alcoholic beverages, including wine, beer, spirits, and unrecorded alcohol. Unrecorded alcohol comprises illicitly produced alcohol and so-called surrogate alcohol not initially intended for human consumption (eg, industrial, cosmetic, or medicinal alcohol). Focus is set on the applicability of rapid-screening methodologies such as infrared or nuclear magnetic resonance spectroscopy, in complement to reference methodologies such as gas or liquid chromatography. Case studies regarding falsification of brand spirits, authentication of vintage wines and spirits, and methanol poisoning outbreaks are presented. The chapter concludes with remarks on future trends, such as the need for establishment of open-source databases with food authenticity data.
Article
Metabolomics is the scientific study of the unique chemical fingerprints that result from specific biochemical processes. It enables the comprehensive detection and quantification of small molecules that are intermediates or end-products of metabolism in a biological sample, such as a grape or yeast. The metabolomics approach also provides for a holistic characterisation of complex chemical transformations and oxidation reactions during winemaking, ageing and transport. The development of metabolomics has made major advances in the last two decades. Improved chromatographic techniques for separation of polar metabolites and enhanced sensitivity and selectivity of nuclear mass resonance and mass spectrometric instrumentation now enable detection and quantification of hundreds of metabolites in a single analysis. New bioinformatics tools and statistics capabilities are available which are key to efficiently analysing and annotating comprehensive datasets. This review provides an overview of analytical methods for untargeted profiling, biomarker discovery and targeted analysis of non-volatile and volatile metabolites. It summarises bioinformatics tools for data processing, data mining and metabolite identification and explores metabolomics approaches which have been successfully employed to comprehensively analyse, annotate and understand the broad chemical diversity in grapes, yeast and wine. It also describes opportunities for the application of metabolomics in grape and wine science and provides an outlook about further development needs and emerging trends.
Chapter
Solvent resonance suppression is an essential technique in modern NMR spectroscopy, especially in biological NMR of proteins, DNA, RNA, carbohydrates and aminoacids. Many methods have been developed for solvent suppression so far. A majority of NMR pulse sequences, particularly the multidimensional ones, contains solvent suppression element in preparation period or before data acquisition. In this contribution, we attempt to provide a brief introduction of the general principles, efficiency and usability of the current solvent suppression techniques.
Article
High-resolution Nuclear Magnetic Resonance (NMR) spectroscopy has many applications in the analysis of food and beverage products, especially in combination with multivariate analysis. Most studies have focused on the composition, raw materials, geographical origin, and quality control of these products. Since the 1H NMR spectrum of beer contains huge water and ethanol resonances with higher signal intensities of them than those of the compounds of interest, it becomes problematic to assign a spectrum. So, these obstacles must be overcome in order to define chemical components in beer and to analyze or obtain meaningful data. In this paper, we will analyze the 1H NMR spectra of different lagers and ales with principal component analysis (PCA) and partial least squares (PLS) methods. The results of multivariate analysis of 1H NMR spectra of lyophilized and raw samples obtained using a standard solvent suppression pulse program are compared and discussed for more exact technique as an informative quality control tool.
Article
Methanol, a hepato- and neurotoxic compound is present in apple-based beverages as a by-product of the enzymatic degradation of pectin. Stable isotope dilution assay (SIDA) employing gas chromatography-mass spectrometry (GC-MS) is the state-of-the-art method for methanol determination in beverages. Despite higher initial investment costs, quantitative ¹H-NMR spectroscopy (qNMR) is a simpler and faster analytical technique to quantify numerous analytes in liquid foods. Beyond targeted analyses, qNMR spectral fingerprints in the product might be used for non-targeted analytical goals, such as adulteration and contamination detections. Here, an existing ¹H-qNMR method used for wine profiling was optimised for methanol quantification in apple-based products, including cross-validation against SIDA-HS-GC-MS method and reference values from interlaboratory trials. The optimisation involved a pivotally important estimation of a correction factor by an external calibration approach, making qNMR results comparable to SIDA-HS-GC-MS. The optimised qNMR method is suggested to be an alternative for methanol quantification in beverages.
Article
Nuclear magnetic resonance (NMR) spectroscopy is a robust method, which can rapidly analyze mixtures at the molecular level without requiring separation and/or purification steps, making it ideal for applications in food science. Despite its increasing popularity among food scientists, NMR is still an underutilized methodology in this area, mainly due to its high cost, relatively low sensitivity, and the lack of NMR expertise by many food scientists. The aim of this review is to help bridge the knowledge gap that may exist when attempting to apply NMR methodologies to the field of food science. We begin by covering the basic principles required to apply NMR to the study of foods and nutrients. A description of the discipline of chemometrics is provided, as the combination of NMR with multivariate statistical analysis is a powerful approach for addressing modern challenges in food science. Furthermore, a comprehensive overview of recent and key applications in the areas of compositional analysis, food authentication, quality control, and human nutrition is provided. In addition to standard NMR techniques, more sophisticated NMR applications are also presented, although limitations, gaps, and potentials are discussed. We hope this review will help scientists gain some of the knowledge required to apply the powerful methodology of NMR to the rich and diverse field of food science.
Article
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A simple and robust solvent suppression technique that enables acquisition of high quality 1D (1) H NMR spectra of alcoholic beverages on cryoprobe instruments was developed and applied to acquire NMR spectra of Scotch Whisky. The method uses three channels to suppress signals of water and ethanol, including those of (13) C satellites of ethanol. It is executed in automation allowing high throughput investigations of alcoholic beverages. Based on the well-established 1D NOESY solvent suppression technique, this method suppresses the solvent at the beginning of the pulse sequence, producing pure phase signals minimally affected by the relaxation. The developed solvent suppression procedure was integrated into several homo- and heterocorrelated 2D NMR experiments, including 2D COSY, 2D TOCSY, 2D band-selective TOCSY, 2D J-resolved spectroscopy, 2D (1) H, (13) C HSQC, 2D (1) H, (13) C HSQC-TOCSY and 2D (1) H, (13) C HMBC. A 1D chemical-shift-selective TOCSY experiments was also modified. The wealth of information obtained by these experiments will assist in NMR structure elucidation of Scotch Whisky congeners and generally the composition of alcoholic beverages at the molecular level.
Article
Barbera is one of the most common red grape in Italy, found in almost every region of the country. The widespread market of the corresponding wine deserves studies on its traceability and authenticity. To this end, the ¹H-NMR database of several wine metabolites was built using spectra recorded in a wine-like matrix containing ethanol and tartaric acid with pH precisely adjusted. The combination of ¹H-NMR metabolomics study and chemometrics (multivariate data analysis) is able to discriminate between samples of such a wine produced in three different areas of Piedmont. The influence of climatic factors on the wine characteristics has also been studied.
Article
Beverage fraud involving counterfeiting of brand spirits is an increasing problem not only due to deception of the consumer but also because it poses health risks e.g. from possible methanol admixture. Suspicious spirit samples from Russia and Kenya were analysed using 1H nuclear magnetic resonance (NMR) spectroscopy in comparison to authentic products. Using linear regression analysis of spectral integral values, 4 counterfeited samples from Russia and 2 from Kenya were easily identifiable with R2 < 0.7. Sensory analysis using triangle test methodology confirmed significant taste differences between counterfeited and authentic samples but the assessors were unable to correctly identify the counterfeited product in the majority of cases. An important conclusion is that consumers cannot assumed to be self-responsible when consuming counterfeit alcohol because there is no general ability to organoleptically detect counterfeit alcohol.
Article
A binomial-like block based multiple suppression NMR pulse sequence, termed MULTI-GATE-FSB, that is simple to implement with outstanding suppression performance for multiple solvent signals (or multiple resonances) is investigated. The sequence was tested on two water-alcohol solvent systems, and a standard lysozyme sample, and with suppression of three or four regions (though it is extendable to any number of regions). The suppression of all solvent signals was possible in the alcohol-water systems tested with both long and short recycle delays, and without the requirement for lengthy pre-saturation pulses. Such a sequence holds promise not only for LC-NMR applications and solvent suppression but for multiple suppression applications in general (e.g., analysis of impurities/components).
Article
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Nuclear magnetic resonance (NMR) spectroscopy is an innovative method for wine analysis. Every grapevine variety has a unique structural formula, which can be considered as the genetic fingerprint of the plant. This specificity appears in the composition of the final product (wine). In the present study, the originality of Hungarian wines was investigated with 1H NMR-spectroscopy considering 861 wine samples of four varieties (Cabernet Sauvignon, Blaufränkisch, Merlot, and Pinot Noir) that were collected from two wine regions (Villány, Eger) in 2015 and 2016. The aim of our analysis was to classify these varieties and region and to select the most important traits from the observed 22 ones (alcohols, sugars, acids, decomposition products, biogene amines, polyphenols, fermentation compounds, etc.) in order to detect their effect in the identification. From the tested four classification methods—linear discriminant analysis (LDA), neural networks (NN), support vector machines (SVM), and random forest (RF)—the last two were the most successful according to their accuracy. Based on 1000 runs for each, we report the classification results and show that NMR analysis completed with machine learning methods such as SVM or RF might be a successfully applicable approach for wine identification.
Article
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Important challenges of wine authentication - for example the proof of wine varieties, the determination of the vintage or the geographical origin, the determination of certain practices (e.g. differentiation of barrel/chips storage) become more and more successfully investigated by non-targeted analytical approaches. Not only in relation to these open questions in wine authentication non-targeted approaches such as nuclear magnetic resonance and mass spectrometry offer enormous potential also in wine authentication due to their typical abilities as high-through put and screening technique. The adaptation from research into routine applications takes actually place in some instances (e.g. NMR) including wine analysis. In addition the combination of non-targeted and targeted approaches within the same run of analysis provides possibilities complementing or even substituting classical methodologies. Some examples, the general workflow and typical evaluation strategies will be presented and their possibilities and limits discussed. First results of a recent study on the NMR analysis with focus on variety verification and reproducibility of spectral data will be presented. Particular emphasis will be put on general open questions such as exchangeability of data, validation, standardisation options.
Article
Scotch Whisky has been analysed as a complex mixture in its raw form using high resolution Nuclear Magnetic Resonance (NMR) and previously developed water and ethanol suppression techniques. This has allowed for the positive identification of 25 compounds in Scotch Whisky by means of comparison to reference standards, spike-in experiments, and advanced 1D and 2D NMR experiments. Quantification of compounds was hindered by signal overlap, though peak alignment strategies were largely successful. Statistical total correlation spectroscopy (STOCSY) yielded information on signals arising from the same compound or compounds of similar origin. Statistical analysis of the spectra was performed using Independent and Principal Components Analysis (ICA, PCA) as well as Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA). Several whisky production parameters were successfully modelled, including blend or malt status, use of peated malt, alcohol strength, generic authentication and maturation wood type, whilst age and geographical origin could not be modelled.
Thesis
Dans un marché globalisé où 40% du vin consommé est importé, le contrôle de la traçabilité est un enjeu majeur de la filière viti-vinicole. L'authentification du vin est le processus pouvant faire appel à différentes méthodes analytiques devant pouvoir contrôler trois paramètres fondamentaux : l’origine géographique, le cépage et le millésime. La spectroscopie RMN 1H quantitative (RMNq) est aujourd'hui considérée comme un outil très prometteur pour l'étude de l'authenticité des vins. Lors de cette thèse, une technique de dosage de 40 composés majoritaires des vins par RMN 1H a été développée. Elle permet l’acquisition d’une information riche et complexe en une seule analyse non-spécifique. La capacité de cette technique à authentifier un vin a été démontrée suite à une collaboration avec le Château Mouton-Rothschild, par comparaisons avec des analyses officielles réalisées par la DGDDI et DGCCRF de Pessac (SCL). La détermination d’un seuil de conformité a été établie en prenant en compte l’évolution naturelle des vins en bouteille. Une étude de caractérisation des vins rouges de Bordeaux a été menée. La singularité de ces vins a été observée par comparaison avec d’autres vins français, mettant en évidence des métabolites caractéristiques des vins de Bordeaux. Les résultats fournissent une description globale du potentiel de la RMN 1H pour l’authentification des vins.
Chapter
Wine is an extremely sophisticated chemical matrix in which the harmonious equilibria between many components (alcohols, acids, aromas, polyphenols, etc.) determine its final quality and value. The study of wine composition by metabolomic tools, referred as Wineomics, has emerged as a revolutionary approach to unravel the chemical space of wines and to associate wine composition with important viticultural and enological traits including grape variety, geographical origin, terroir or typicity. One of the most promising applications of metabolomic tools for wine analysis is the study of wine traceability and authenticity, a major issue for the wine industry and consumers. These studies are extremely complex, because counterfeits are becoming more sophisticated and they require powerful techniques capable to detect subtle differences between wines. In this chapter, we describe the targeted and untargeted approaches by Mass and NMR spectrometry-based metabolomics as well as some recent examples of their abilities in wine authenticity studies.
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Alcoholic beverages have a complex chemistry that can be influenced by their alcoholic content, origin, fermentation process, additives, and contaminants. The complex composition of these beverages leave them susceptible to fraud, potentially compromising their authenticity, quality, and market value, thus increasing risks to consumers’ health. In recent years, intensive studies have been carried out on alcoholic beverages using different analytical techniques to evaluate the authenticity, variety, age, and fermentation processes that were used. Among these techniques, NMR-based metabolomics holds promise in profiling the chemistry of alcoholic beverages, especially in Asia where metabolomics studies on alcoholic beverages remain limited.
Article
The wine industry routinely employs sulphur dioxide (SO2) as an additive for antiseptic, antioxidasic and antioxidant activities. Some of the most important wine metabolites such as acetaldehyde, diacetyl, pyruvic acid, α-ketoglutaric acid, hydroxymethylfurfural, furfural and acetoin are known to react with SO2 over time to form adducts. ¹H NMR spectroscopy of wine can be tricky as metabolites exist either in original form or as O-adducts or as S-adducts at different SO2 concentrations. We are proposing a methodology for metabolites identification including all the possible SO2 generated species. ¹H NMR spectroscopy is able to highlight the structural changes that a metabolite undergoes in wine in the presence of SO2. The ¹H NMR spectra of the main wine metabolites known to react with SO2 were recorded in wine-model solutions at SO2 concentrations at 0, 50, 100 and 150 mg/L that are all below the maximum level allowed by the European Union regulations. Acetaldehyde was completely transformed into the corresponding hydroxysulfonate at a SO2 concentration of 100 mg/L. The concentration of this metabolite was assayed in ten commercial Moscato wine samples including the 1H NMR resonances of all its identified forms. The results corresponded to those determined according to the OIV standard protocols.
Article
Distillation fractions (head, body, and tail) and mezcal samples were analyzed by proton nuclear magnetic resonance spectroscopy (1H-NMR). Samples were obtained from five rural producers in Oaxaca State, Mexico, where the distilled beverage was produced using as raw material Agave angustifolia, commonly known as “Espadín”. The distillation cuts were done by the producers according to their experience and samples were taken from each distillation fraction. 1H-NMR spectra were acquired by two sample preparation methods: direct analysis (DA) and solid-phase extraction (SPE) using styrene–divinylbenzene sorbent to concentrate aromatic compounds. When DA-NMR was used, fifteen compounds were identified and quantitated at mg/L level, including higher alcohols, aldehydes, esters, and organic acids. On the other hand, nine compounds were identified by SPE-NMR, including fatty acids, aromatic alcohols, aldehydes, and polycyclic aromatic hydrocarbons. The study showed that 1H-NMR can be done by DA and with SPE as a complementary method for analysis of mezcal and its distillation fractions. These methodologies are useful for both research and industrial purposes.
Article
The temperature effect of simulated transport conditions on wine quality was investigated. Transport situations were simulated in a climate chamber for five wines representing international wine styles: one sparkling, two white and two red still wines. The wines were exposed to temperature scenarios over a maximum time of 42 days at temperature ranges between 15 and 40 °C and the control storage at 15 °C. Analytical and sensory results demonstrated that a significant temperature influence, calculated as a temperature-time equivalence needs to be reached before quality effects are observed. The wines of a fruity and lighter style (red Pinot Noir and Sauvignon Blanc wines from 2017 vintage) were more sensitive than the wines with higher alcohol and wooden aging (red Bordeaux and Chardonnay wines from 2015 vintage). Except for the Champagne, sensory examinations showed a regular linear trend with exposure severity starting at the time equivalence at 15 °C. The sensory results correlated well with the UV–vis and HS-SPME-GC–MS results.
Article
Non-targeted Nuclear Magnetic Resonance (NMR) spectroscopy is a promising approach for wine authentication. A prerequisite for its application in official control is the inter-laboratory comparability, which has rarely been the subject of research studies so far. For the first time, in this study an instrument comparison was carried out in order to investigate the extent and impact of instrumental differences on the classification of wine grape varieties. Following a harmonized protocol for sample preparation, spectra acquisition and processing, the same sample set, comprising of 101 red and 100 white wine samples, was analyzed with two NMR spectrometers of the same vendor in different laboratories. Observed spectral differences (intensity, baseline, chemical shift of pH-sensitive signals) were accounted for by applying an instrument-specific conversion factor or normalization to total intensity, respectively. Partial Least Squares – Discriminant Analysis (PLS-DA) and Principal Component Analysis – Linear Discriminant Analysis (PCA-LDA) classification models built with data from the individual instruments and with combined data from both instruments achieved comparable accuracies in the internal validation (79–87%). When classification models of the individual instruments were used to predict data of the respective other instrument, results were inconsistent, whereas the use of combined data from both instruments for training and test sets produced more robust and reliable results. This study represents an important step towards harmonization of non-targeted analytical approaches and may help in the development of jointly used databases for food authentication.
Article
An overview of alcoholic beverages discrimination plus the author’s experimental research work on identification of bland Chinese liquors is presented in this article. First, a summary was given on analytical techniques combined with multivariate statistical analysis for discrimination problems related to alcoholic beverages; and then, our experimental research was presented on discrimination of different aroma types of Chinese liquors by ¹H-Nuclear Magnetic Resonance (NMR) and ¹³C-NMR combined with multivariate statistical analysis. Principal Component Analysis (PCA) was used to highlight the most significant features from high-dimensional data to acquire visual inspections of NMR spectra in the first step. The representative new score values were used as the input variables for Support Vector Machine (SVM), and the performance of this model was evaluated by Leave-One-Out Cross Validation method (LOOCV). Compared with ¹H-NMR, the scores of PCA and predications of the SVM model from ¹³C-NMR spectra showed more significant separation and better prediction performance. ¹³C-NMR for multivariate analysis might be a more effective tool for identification of these Chinese liquors because of its complementary component information as well as less spectral overlapping than that in ¹H-NMR.
Chapter
1H NMR profiling is an emerging technique for the characterization of food quality, authenticity, origin and stability and for the study of food production, transformation and storage processes. To produce reliable results, a large number of good quality NMR spectra are needed together with suitable processing and pattern recognition algorithms. Different aspects of sample preparation and spectra detection and quantification are discussed together with the most diffused pattern recognition methods which permit to associate NMR spectra to food macroscopic properties. Critical aspects of clustering, classification and regression approaches are analysed and the importance of model validation and data representation emphasized. Finally, the most important applications of 1H NMR profiling to food science are presented.
Article
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Although vodka is a reasonably pure mixture of alcohol and water, beverage drinks typically show differences in appeal among brands. The question immediately arises as to the molecular basis, if any, of vodka taste perception. This study shows that commercial vodkas differ measurably from ethanol-water solutions. Specifically, differences in hydrogen-bonding strength among vodkas are observed by (1)H NMR, FT-IR, and Raman spectroscopy. Component analysis of the FT-IR and Raman data reveals a water-rich hydrate of composition E x (5.3 +/- 0.1)H(2)O prevalent in both vodka and water-ethanol solutions. This composition is close to that of a clathrate-hydrate observed at low temperature, implying a cage-like morphology. A structurability parameter (SP) is defined by the concentration of the E x (5.3 +/- 0.1)H(2)O hydrate compared to pure ethanol-water at the same alcohol content. SP thus measures the deviation of vodka from "clean" ethanol-water solutions. SP quantifies the effect of a variety of trace compounds present in vodka. It is argued that the hydrate structure E x (5.3 +/- 0.1)H(2)O and its content are related to the perception of vodka.
Article
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The hydrogen-bonding structure of water-ethanol in whiskey was examined on the basis of (1)H NMR chemical shifts of the OH of water and ethanol. Phenolic acids and aldehydes (gallic, vanillic, and syringic acids; vanillin and syringaldehyde) exhibited their structure-making effects regardless of the presence or absence of 0.1 or 0.2 mol dm(-3) acetic acid. The OH-proton chemical shifts were measured for 32 malt whiskey samples of a distillery, aged for 0-23 years in five different types of casks. The OH-proton chemical shift values of the whiskies shifted toward the lower field in proportion to their contents of total phenols. It can be concluded that the strength of the hydrogen bonding in aged whiskies is directly predominated by acidic and phenolic components gained in oak wood casks and not dependent on just the aging time.
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A previous publication (Kokkinofta et al. J. Agric. Food Chem. 2003, 51, 6233-6239) discussed the use of inductively coupled plasma spectroscopy to differentiate between the traditional Cypriot alcoholic beverage zivania and other spirits similar in alcoholic content collected from different countries. In the present paper (1)H NMR spectroscopy is applied to confirm the previous conclusions and to obtain additional physical-chemical characteristics that may be used to differentiate zivania from other similar beverages. NMR spectroscopy gave a satisfactory degree of prediction and classification between zivanias and other distillings. The validity of quantification of the method was tested using comparative GC data. It appears that chemical analysis can be very helpful for identifying the unique geological and climatic conditions existing in the island of Cyprus that lead to an authentic product.
Article
A modification of the excitation sculpting sequence [Hwang, T.-L. and Shaka, A.J. (1995) J. Magn. Reson., A112, 275-279] for achieving efficient multiple-solvents suppression in 1D and 2D H-1 NMR experiments is presented. Implementation of this scheme in the ePHOGSY experiment allows rapid and sensitive detection of weak interactions between organic solvents or small molecules and biomolecules. Application of the techniques to the peptide Sandostatin (R) dissolved in H2O and DMSO is demonstrated.
Article
An interesting and simple approach to effective multiple-solvent suppression is proposed using the basic principles of the excitation sculpting methodology. Flat baseline and ultra-clean NMR spectra are usually obtained under standard conditions using a modified double pulsed field gradient echo scheme in samples con-taining mixtures of non-deuterated solvents. The simple performance of such an approach, the high tolerance to experimental mis-settings, the impressive level of solvent suppression and the easy incorporation of the proposed scheme in multi-dimensional NMR experiments make this method suitable for possible applications in liquid chromatography NMR. © 1998 John Wiley & Sons, Ltd.
Article
High-resolution nuclear magnetic resonance (NMR) spectroscopy is introduced for the quality control and authenticity assessment of beer in official food control. Measurements were performed using a 400-MHz NMR spectrometer using flow injection technology for automatic sample changing. Only degassing and addition of buffer (pH 5.6 in D2O for locking and 0.1% TSP for referencing) is required to prepare the beer samples. Differences in the spectral profiles of beers varying in type and origin were studied by principal component analysis (PCA), considering the spectrum to be a characteristic fingerprint. For the first time, the high throughput of a Flow-Injection NMR system allowed a comprehensive database of beer spectra for PCA classification to be established efficiently. Beers made with barley malt could be distinguished from those made with wheat malt. Clustering of beers from the same brewing sites was observed, as well as significant discrimination of beers with deteriorated quality. Using the partial least squares (PLS) method to correlate NMR spectra with results from reference methods, models for calculating the original gravity, ethanol and lactic acid were established. The results obtained suggest that NMR is a useful tool in the quality control of beer samples, since quantitative determination of essential compounds as well as chemometric classification are simultaneously possible. Compared to conventional methods, 1H NMR spectroscopy is faster and requires simpler sample preparation.
Article
Low-resolution pulsed nuclear magnetic resonance may be used to determine the ethanol concentration in alcoholic beverages. The measurement is based on the J echo modulation of NMR signals for an ethanol sample, which goes through a maximum at a refocusing time of 1/(2J) equals 68 ms. A linear relationship is obtained between the percentage of ethanol (v/v) and the amplitude of the echo modulation either in a simple ethanol solution or in more complex media such as wines and spirits. The accuracy of the method depends on the choice of the medium used for the calibration curve and can reach 0. 2 vol% ( sigma ) over a range as wide as 0-70%. This fast and nondestructive determination of alcohol, using a low-cost NMR spectrometer, could be a good alternative for on-line control of fermentation processes in an industrial environment.
Article
A simple method of generating frequency-shifted pulses is demonstrated for any spectrometer which is capable of generating an extended series of amplitude- and phase-modulated RF pulses. This method can be combined with existing methods of selective excitation to produce single- or multiple-frequency-selective pulses, or can be combined with “hard” pulses for experiments in which it is desired to place the center of excitation at a location other than that of the receiver for part or all of a pulse sequence. Because the frequency “shifts” described here occur instantaneously with complete phase continuity and can excite multiple frequencies simultaneously, they offer strong advantages over methods involving actual frequency shifts.
Article
Solvent signal suppression in Nuclear Magnetic Resonance (NMR) has been reported. a few techniques have been developed for the suppression of radiation damping, easier pulse sequence based radiation damping suppression methods which are compatible with common solvent suppression schemes are required. The performance of suppression methods is often illustrated on (biomolecular) samples with relatively high concentrations under ideal conditions while in reality the intended application is for samples at super low concentrations. As the availability of higher field clinical MRI equipment becomes more widespread in conjunction with the development of digitizers with higher resolution and more efficient methods for the suppression of sideband modulation, in vivo NMR experiments without water suppression will find more and more applications in medicine. This will also spur greater developments in post-acquisition data processing.
Article
An important recent development in NMR spectroscopy is the advent of ex situ dynamic nuclear polarization (DNP) approaches, which are capable of yielding liquid-state sensitivities that exceed considerably those afforded by the highest-field spectrometers. This increase in sensitivity has triggered new research avenues, particularly concerning the in vivo monitoring of metabolism and disease by NMR spectroscopy. So far such gains have mainly materialized for experiments that focus on nonprotonated, low-γ nuclei; targets favored by relatively long relaxation times T(1), which enable them to withstand the transfer from the cryogenic hyperpolarizer to the reacting centers of interest. Recent studies have also shown that transferring this hyperpolarization to protons by indirectly detected methods could successfully give rise to (1)H NMR spectra of hyperpolarized compounds with a high sensitivity. The present study demonstrates that, when merged with spatially encoded methods, indirectly detected (1)H NMR spectroscopy can also be exploited as time-resolved hyperpolarized spectroscopy. A methodology is thus introduced that can successfully deliver a series of hyperpolarized (1)H NMR spectra over a minutes-long timescale. The principles and opportunities presented by this approach are exemplified by following the in vitro phosphorylation of choline by choline kinase, a potential metabolic marker of cancer; and by tracking acetylcholine's hydrolysis by acetylcholine esterase, an important enzyme partaking in synaptic transmission and neuronal degradation.
Article
The recent melamine crisis in China has pointed out a serious deficiency in current food control systems, namely, they specifically focus on selected known compounds. This targeted approach allowed the presence of melamine in milk products to be overlooked for a considerable time. To avoid such crises in the future, we propose that nontargeted screening methods need to be developed and applied. To this end, NMR has an extraordinary potential that just started to be recognized and exploited. Our research shows that, from the very same set of spectra, (1)H NMR at 400 MHz can distinguish between melamine-contaminated and melamine-free infant formulas and can provide quantitative information by integration of individual lines after identification. For contaminated Chinese infant formulas or candy, identical results were obtained when comparing NMR with SPE-LC/MS/MS. NMR was found to be suitable for routine nontargeted and targeted analyses of foods, and its use will significantly increase food safety.
Article
We explored the possibility of differentiating Italian wines produced in different regions by means of nuclear magnetic resonance (NMR) techniques. Ten commercial red Aglianico wines were selected from different areas of the Basilicata region in the south of Italy. Some important components of these wines were identified by the assignments of their (1)H and (13)C resonances using one- and two-dimensional homonuclear and heteronuclear NMR experiments. These data were compared with those obtained from 10 Aglianico wines produced in Campania, another southern Italian region. Differences were found among the wines according to their geographical origin and vintage. A fine discrimination of Aglianico wines from Basilicata and Campania was obtained, suggesting that the selected NMR parameters may be a valuable tool for wine authenticity control.
Article
Amino acids are minor compounds in wines, but they have a profound influence on wine quality, and amino acids composition can be used to differentiate wines according to the vine variety, geographical origin, and year of production. The NMR signals of amino acids in NMR spectra are overlapped by the signals of other compounds present and especially by the signals of dominant compounds such as water, ethanol, and glycerol. In this work we used 1D (1)H and (13)C, 2D homonuclear COSY, TOCSY, and 2D heteronuclear HSQC and HMQC pulse sequences, also with an incorporated WET pulse sequence element that allows the simultaneous suppression of several frequencies. Complete (1)H and (13)C NMR assignments for 17 amino acids commonly present in wine and of gamma-aminobutyric acid at pH 3 have been achieved in wine sample of Sauvignon from the Coastal wine-growing region of Slovenia, vintage 1994.
Article
Excitation sculpting was first introduced as a way to efficiently suppress solvent signals. It requires a pulse sequence that acts as a null pulse at the solvent-resonance frequency and as an inversion pulse everywhere else. In this article, it is shown that such a goal can be achieved starting with "top-hat" inversion shaped pulses such as I-BURP-2 or gaussian cascade G3. The result is a Globally Antisymmetric Selective Pulse, or GASP. Numerical optimization was used to extend the performance of such pulses. Multifrequency signal suppression was shown to be possible through application of successive excitation sculpting modules.
Article
Pulse sequences have been developed that add up time-resolved photo-CIDNP signals from n successive laser flashes not in the acquisition computer of the NMR spectrometer but in the experiment itself, resulting in a greatly improved signal-to-noise ratio. For this accumulation, CIDNP is first stored in the transverse plane and then on the z axis, and finally superimposed on CIDNP produced by the next flash. These storage cycles also result in a very efficient background suppression. Because only one free induction decay is acquired for n flashes, the noise is digitized only once. The signal gain is demonstrated experimentally and analyzed theoretically. Losses are mostly due to nuclear spin relaxation, and to a small extent to instrument imperfections. With 10 laser flashes, a signal increase by a factor of about 7.5 was realized. As their main advantage compared to signal averaging in the usual way, these sequences yield the same signal-to-noise ratio with fewer laser flashes; the theoretical improvement is by a factor of n.
Article
This work presents the capability of NMR spectroscopy combined with Chemometrics in predicting the ageing of Balsamic and Traditional Balsamic Vinegar of Modena. The need of an analytical method is an important requirement for both research oriented and commercial evaluation of these very valuable products. (1)H NMR spectroscopy, based on the advantage of rapid sample analysis without any manipulation or derivatization, is here proposed as a valid tool to describe Balsamic and Traditional Balsamic Vinegar of Modena. For this purpose, 72 reliable samples, were divided into three different groups according to their ageing process: young (<12 years), old (>12 and <25 years) and extra old (>25 years). Hierarchical Projection to Latent Structures Discriminant Analysis (PLS-DA) allowed us to characterize the ageing process. Variables showing the largest VIP (Variable Importance in the Projection) were extracted from PLS-DA model, thus shedding lights onto the role played by specific compounds in this complex ageing process. Two robust classification models, were built by PLS-DA and Naïve Bayes classifier and compared to prove the accuracy of the representation on both training and test sets. The predictions obtained for 41 "unknown" vinegar samples with these both methods gave more than 80% agreement among them.
Article
Metabolite profiling relies on optimal precision of the acquired data, which requires, among others, a high signal-to-noise ratio (S/N). In addition, increased S/N will increase the likelihood of identification of new biomarkers. Here we introduce, for the first time in metabolite profiling studies by 1H NMR, an approach to enhance the precision of multivariate regression models by use of the FLIPSY (flip angle adjustable one-dimensional NOESY) pulse sequence, augmented by a homospoil pulse after the presaturation period to provide superior baseline quality. Unlike NOESYPRESAT, the standard one-dimensional (1D) sequence generally used in metabonomic studies, FLIPSY incorporates a variable flip angle, allowing use of the Ernst angle for excitation and thus optimization of S/N ratios according to spin lattice relaxation times (T1) of individual resonances. T1 values of metabolites present in human urine were determined by inversion-recovery experiments and subsequently used in calculations of optimal experimental conditions. Comparison of human urine analysis by the FLIPSY and NOESYPRESAT demonstrated an increase of S/N ratio in the former case that amounts to approximately 7% when measured for the hippurate doublet at delta 7.84. An orthogonal projection to latent structures discriminant analysis (O-PLS-DA) model exhibited superior discrimination between controls and simulated phenylketonuria urines when using data generated by the FLIPSY as compared to NOESYPRESAT.
Article
The quality of data measured in in vivo MR spectroscopy is often insufficient due to a number of limitations such as low concentrations of observed metabolites and restricted measurement time resulting in a low signal-to-noise ratio. However, there are a variety of methods called post-processing techniques which allow the enhancement of the measured signal after measurement. In this review an introduction to the most important post-processing techniques for (1)H MR spectroscopy is given and practical examples are shown. In the first section the concept of FID and spectrum is introduced and the relationship between FID and spectrum is explained. Subsequently, the objectives and description of the following post-processing techniques are provided: eddy current correction, removal of an unwanted component (water), signal filtering for various purposes, zero filling, phase correction and baseline correction.
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