Magnetic Resonance in Chemistry

Merkx, Donny W.H.; Delić, Faruk; Wierenga, Peter A.; Hennebelle, Marie; Duynhoven, John P.M.

doi: 10.1002/mrc.4808pmid: 30474149

Lipid oxidation is the main reason for the limited shelf life of mayonnaise. One of the main catalysts of this process is iron, which is introduced in its ferric (Fe(III)) form via phosvitin, an egg yolk phosphoprotein rich in phosphoserines. The binding of Fe(III) to phosvitin and its ability to establish a redox couple with Fe(II) is believed to determine the oxidation rate of unsaturated lipids. In this work, a 31P NMR based method was developed to quantify loading of phosvitin with Fe(III) and its reductive release. Both features could be quantified in model phosvitin solutions by exploiting the paramagnetic broadening of 31P NMR signal of phosphoserine residues by Fe(III). This method was then successfully applied to quantify the phosvitin‐Fe(III) loading in mayonnaise water phase by liquid NMR, whereas 31P NMR MAS could only provide a qualitative measure. The 31P NMR method showed a direct relation between loading of the Fe(III)‐phosvitin complex and lipid oxidation.

Roo, Niels; Wilmsen, Sanne M. J.; Mihaleva, Velitchka V.; Jacobs, Doris M.; Duynhoven, John P. M.

doi: 10.1002/mrc.4833pmid: 30658005

The health benefits of black tea have been linked to polyphenol metabolites that target specific modes of action in the human body. A major bottleneck in unravelling the underlying mechanisms is the preparative isolation of these metabolites, which hampers their structural elucidation and assessment of in vitro bioactivity. A solid phase extraction (SPE)‐preparative liquid chromatography (prepLC)–MS–LC–MS‐NMR workflow was implemented for preparative isolation of conjugated valerolactone metabolites of catechin‐based polyphenols from urine of black tea consumers. First, the urine was cleaned and preconcentrated using an SPE method. Subsequently, the clean urine concentrate was injected on a preparative LC column, and conjugated valerolactones were obtained by MS‐guided collection. Reconstituted fractions were further separated on an analytical LC column, and valerolactone fractions were collected in an MS‐guided manner. These were reconstituted in methanol‐d4 and identified and quantified using 1D and 2D homo‐ and hetereonuclear NMR experiments (at a field strength of 14.1 T), in combination with mass spectrometry. This resulted in the full spectral 1H and 13C NMR assignments of five conjugated valerolactones. These metabolites were collected in quantities of 8–160 μg and purities of 70–91%. The SPE‐prepLC–MS–LC–MS‐NMR workflow is suitable for isolating metabolites that occur at sub‐μM concentrations in a complex biofluid such as urine. The workflow also provides an alternative for cumbersome and expensive de novo synthesis of tea metabolites for testing in bioactivity assays or for use as authentic analytical standards for quantification by mass spectrometry.

Consonni, Roberto; Cagliani, Laura Ruth

doi: 10.1002/mrc.4807pmid: 30447115

In the last years, there was an increasing interest on nuclear magnetic resonance (NMR) spectroscopy, whose applications experienced an exponential growth in several research fields, particularly in food science. NMR was initially developed as the elective technique for structure elucidation of single molecules and nowadays is playing a dominant role in complex mixtures investigations. In the era of the “omics” techniques, NMR was rapidly enrolled as one of the most powerful methods to approach metabolomics studies. Its use in analytical routines, characterized by rapid and reproducible measurements, would provide the identification of a wide range of chemical compounds simultaneously, disclosing sophisticated frauds or addressing the geographical origin, as well as revealing potential markers for other authentication purposes. The great economic value of high‐quality or guaranteed foods demands highly detailed characterization to protect both consumers and producers from frauds. The present scenario suggests metabolomics as the privileged approach of modern analytical studies for the next decades. The large potentiality of high‐resolution NMR techniques is here presented through specific applications and using different approaches focused on the authentication process of some foods, like tomato paste, saffron, honey, roasted coffee, and balsamic and traditional balsamic vinegar of Modena, with a particular focus on geographical origin characterization, ageing determination, and fraud detection.

Ackermann, Svenja M.; Lachenmeier, Dirk W.; Kuballa, Thomas; Schütz, Birk; Spraul, Manfred; Bunzel, Mirko

doi: 10.1002/mrc.4838pmid: 30680787

Both the German and European organic food markets are growing fast, and there is also a rising demand for organic chicken eggs. Consumers are willing to pay higher prices for organic eggs produced in an animal‐appropriate environment considering animal welfare. Strict labelling requirements do not prevent chicken eggs from being a subject of food fraud. Conventionally produced (barn/free‐range) eggs can easily be mislabeled as organic eggs. Especially because the demand for organically produced chicken eggs is likely to exceed supply in the future, mislabeling appears to be a realistic scenario. Therefore, there is a need for analytical methods that are suitable to classify eggs as being either conventionally or organically produced.

Febvay, Laura; Hamon, Erwann; Recht, Raphaël; Andres, Nicolas; Vincent, Mathilde; Aoudé‐Werner, Dalal; This, Hervé

doi: 10.1002/mrc.4834pmid: 30664274

Roasting of Coffea arabica L. seeds gives rise to chemical reactions that produce more than 800 compounds, some being responsible for the desired organoleptic properties for which the beverage called “coffee” is known. In the industry, the “roasting profile,” that is, the times and temperatures applied, is key to influence the composition of roasted coffee beans and the flavour of the beverage made from them. The impact of roasting on the chemical composition of coffee has been the subject of numerous studies, including by nuclear magnetic resonance (NMR) spectroscopy. However, the roasting equipment and profiles applied in these studies are often far from real industrial conditions.

Rodríguez‐Alonso, Elvira; Vergeldt, Frank J.; Goot, Atze Jan

doi: 10.1002/mrc.4815pmid: N/A

Grunin, Leonid; Oztop, Mecit Halil; Guner, Selen; Baltaci, Saadet Fatma

doi: 10.1002/mrc.4866pmid: 30868656

Time‐domain nuclear magnetic resonance techniques are frequently used in polymer, pharmaceutical, and food industries as they offer rapid experimentation and generally do not require any considerable preliminary sample preparation. Detection of solid and liquid fractions in a sample is possible with the free induction decay (FID). However, for the classical FID sequence that consists of a single pulse followed by relaxation decay acquisition, the dead time of the probe (ring out of resonance circuitry) occurs and varies between 5 and 15 μs for standard 10‐mm tubes. In such a case, there arises a risk that the signal from the solid fraction cannot be detected correctly. To obtain quantitative measurement on crystalline and more mobile amorphous fractions, alternative sequences to the classical FID in the solid‐state nuclear magnetic resonance were developed. Solid echo and magic sandwich echo sequences perform the relaxation decay refocusing somehow excluding the dead time problem and allow detection of the signal from the solid fraction. In this study, knowledge of amorphous/crystal fraction, which is obtained through solid echo and magic sandwich echo, has been explored on powder sugar samples for the purpose of developing a groundwork for a reliable quality control method. Different sugars were examined for the utilization of the sequences. What is important to add and make this study unique is that the method proposed did not involve multiparameter fitting of the “bead” pattern FID signal that normally suffers from ambiguity; just the integration of the fast Fourier transform of the solid echo was needed to calculate the second moment, (M2).

Monaretto, Tatiana; Souza, Andre; Moraes, Tiago Bueno; Bertucci‐Neto, Victor; Rondeau‐Mouro, Corinne; Colnago, Luiz Alberto

doi: 10.1002/mrc.4806pmid: 30443995

The traditional way to enhance signal‐to‐noise ratio (SNR) of nuclear magnetic resonance (NMR) signals is to increase the number of scans. However, this procedure increases the measuring time that can be prohibitive for some applications. Therefore, we have tested the use of several post‐acquisition digital filters to enhance SNR up to one order of magnitude in time domain NMR (TD‐NMR) relaxation measurements. The procedures were studied using continuous wave free precession (CWFP‐T1) signals, acquired with very low flip angles that contain six times more noise than the Carr–Purcell–Meiboom–Gill (CPMG) signal of the same sample and experimental time. Linear (LI) and logarithmic (LO) data compression, low‐pass infinity impulse response (LP), Savitzky–Golay (SG), and wavelet transform (WA) post‐acquisition filters enhanced the SNR of the CWFP‐T1 signals by at least six times. The best filters were LO, SG, and WA that have high enhancement in SNR without significant distortions in the ILT relaxation distribution data. Therefore, it was demonstrated that these post‐acquisition digital filters could be a useful way to denoise CWFP‐T1, as well as CPMG noisy signals, and consequently reducing the experimental time. It was also demonstrated that filtered CWFP‐T1 method has the potential to be a rapid and nondestructive method to measure fat content in beef and certainly in other meat samples.