Magnetic Resonance in Chemistry

NMR spectroscopy can play a significant role, complementary to other analytical methodologies, to control and verify the quality and authenticity of olive oils. Information on the geographical origin and variety of olive oils can be obtained using NMR spectroscopy coupled with a suitable multivariate statistical analysis. Some examples of the most significant results obtained in the last 10 years of NMR studies on olive oil are reported.

NMR is successfully being used to characterize wine and find an association of metabolite with environmental and fermentative factors in grape and wine, through global profiling of metabolite in grape and wine, which is coupled with multivariate statistical analysis, called metabolomics. In particular, NMR serves as one of the major analytical approaches in metabolomics, producing information-rich, highly reliable and reproducible data set.

Nuclear magnetic resonance profiling is used for the identification and quantification of the content of mixtures of different kinds of milk. The relative amount of sheep and cow milk is evaluated, by multilinear regression of a selected set of NMR variables, with a precision of about 10%.

The current paper describes the limitations of using NMR spectroscopy to study the phenolic content of grape juices without pre-extraction. A method is described which significantly enhances the accessible information content from NMR-spectroscopy based profiling of grape juice phenols, hence later facilitating identification of these species.

The use of Nuclear Magnetic Resonance (NMR) spectroscopy for beer characterization and quality control is described. Firstly, the qualitative characterization of beer by NMR is reviewed, considering both beer extracts and direct beer analysis. Secondly, NMR studies envisaging the development of rapid methodologies for beer analysis are presented, including Site-Specific Natural Fractionation (SNIF)-NMR and multivariate data analysis (MVDA) of NMR data. Finally, possible future perspectives are briefly discussed.

Scheme describing the symbiotic relationship among the host and their gut bacteria, with the metabolic influence of gut microbiota in a variety of different tissues underpinning the depth of symbiotic control over multiple host cell metabolic regulatory functions.

Fast and reliable metabolite identification based on automated MS-guided HPLC-MS-SPE-NMR metabolite extraction combined with an automated 1H NMR spectrum fitting was developed. Positional isomers as structure 1 and 2 were easily distinguished.

Two different kinds of Parmigiano Reggiano, aged 15 and 30 months, were separately digested using an in vitro system. Samples were collected at different stages of digestion and the process of protein hydrolysis was explored and compared by low-field (LF) and high-resolution (HR) NMR, together with other biochemical methods (Bradford assay and SDS-PAGE).

In the present study time-domain proton NMR relaxometry and high-resolution proton NMR spectroscopy were applied to study the quality of meat obtained from uncommon and novel pig crossings between the rare Iberian and Mangalitza pigs and the more frequent Duroc and Landrace/Yorkshire pigs. Differences in the T₂ relaxation pattern and the metabolite profile of the meat between the different crossings were found. In conclusion, the different NMR techniques applied could provide complementary information about biophysical and biochemical factors of importance for meat quality when new pig breeds are introduced.

A natural extension of the traditional single-PFG technique comprises multiple pairs of diffusion gradients making it possible to characterize anisotropy at different length scales without the need to employ very strong gradients. Experiments on controlled glass capillary arrays yielded quantitatively accurate image contrast dependent on the pore size. By incorporating the fiber orientation information from diffusion tensor imaging (DTI) into the double-PFG framework, the cell size in the vascular bundles of the celery stalk was measured noninvasively.

Arabinoxylans (AXs) extracted from wheat flour were characterized by using three different techniques of NMR spectroscopy. Three pure AX fractions exhibiting an arabinose to xylose ratio of 0.33, 0.53, and 0.73 were compared relative to their substitution feature and also to their assembly into thin films. Comparison of the different AX films containing various water contents pointed out stronger dipolar interactions for lowly substituted AX in relation with a more compact structure with small nanopores.

Low- and high-field NMR methods and data analysis tools are presented and discussed for the determination of droplet size distributions of emulsions. Not only single emulsions with mono- and bi-modal distributions, but also the more complex double emulsions can be characterised. Size distributions of inner droplets of double emulsions, obtained by low- and high-field NMR are compared with results of statistical analysis of CLSM images.

Spin label oximetry, an electron spin resonance (ESR) methodology based on the bimolecular collision between oxygen and a spin label, is capable of detecting dissolved oxygen concentration. The line width in an ESR spectrum for the spin label is dependent on the increase/decrease in oxygen concentration, enabling qualitative and quantitative analysis of continuing oxygen generation or consumption. Therefore, ESR spectroscopy could be readily adaptable for applications in food and biological systems.

The application of continuous wave free precession (CWFP) in rapid analyses of oil and fat content in agri-food by TD-NMR is reviewed. The technique improves the sensitivity approximately one order of magnitude compared with the FID acquired in quantitative conditions. In addition, interesting applications like rapid method for relaxation times measurements and true online analysis are also highlighted.

High resolution magic angle spinning is a powerful tool in food science. It is based on magnetic resonance spectroscopy and can be used efficiently in assessing the metabolic profile of, in principle, any foodstuff, and determining the macromolecular aggregation. The approach is demonstrated to be quick, reliable opening up several possibilities in food characterization.

The problem of characterising the behaviour of water and biopolymers by NMR in low water content biopolymer systems is discussed. It is suggested that any successful model must take account of at least three separate pools of water including water vapour. In spite of the formidable experimental and theoretical difficulties ¹⁷O NMR may be the best way of elucidating the relevant interactions involved.