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High-resolution nuclear magnetic resonance (NMR) spectroscopy has increasingly been used to provide direct and comprehensive compositional information on food complex mixtures. The ability of ^1H NMR to detect a wide type of compounds simultaneously and non-invasively makes it an important potential tool for the quality control of fruit juices. Such approach is distinct from the well-established Site-specific Nuclear Isotope Fractionation (SNIF)-NMR method which usually involves ^2H observation for the measurement of isotopic ratios and correlation with metabolite origins; this subject will not be described here since it justifies in itself a separate entry in this handbook. Furthermore, this entry will mostly deal with accounts of direct NMR analysis of whole juices, rather than of juice extracts, unless otherwise specified.

Applications of high resolution deuterium-NMR in organic and bioorganic chemistry have regularly expanded in the last decades, accompanying the development of high field spectrometers which are required to overcome, at least in part, the severe drawbacks resulting from the nuclear properties of deuterium. In the technological conditions of the seventies both the small gyromagnetic ratio (4.107 × 10^7 rad/s/T), responsible for poor intrinsic sensitivity (9.6 × 10^−3 with respect to ^1H), and the very low natural abundance of deuterium (1.5 × 10^−4) were serious impediments to the study of natural abundance deuterium spectra. Fortunately, the predominance of quadrupolar relaxation avoids perturbations in signal intensities due to nuclear Overhauser effects. Since 1980, more than 300 articles have been published in the field of high resolution ^2H-NMR and, in this number, about 200 are concerned with quantitative determinations of isotope ratios, for which we have proposed the terminology SNIF-NMR (site-specific natural isotope fractionation studied by nuclear magnetic resonance). Both the first paper dealing with the NMR determination of non-random distributions of deuterium and the corresponding patent concerning applications appeared in 1981 [1,2].

Isotope labeling is a privileged source of information on chemical and biochemical mechanisms. In this context, the SNIF-NMR approach, which quantifies non-random distributions of isotopes at the natural abundance level, can be considered as a labeling method devoid of the need for isotopic enrichment [1]. Consequently, in its fields of application, it benefits from specific advantages with respect to conventional labeling methods. In particular, it avoids time-consuming syntheses of selectively labeled precursors, enables all monolabeled isotopomers of a molecular species to be simultaneously compared in identical experimental conditions, and provides a unique strategy for investigating mechanistic pathways taking place in unperturbed conditions. The main limitations are due to the rather poor sensitivity and chemical shift resolution of ^2H-NMR (cf. Part 1), which preclude observation of complex metabolites present in very diluted media or available only at the submilligram level.

In contrast to many other analytical parameters, which are mostly exploited on semi-empirical bases, the SNIF-NMR parameters rest on the well-established theoretical principles of isotope fractionation (Parts 1 and 2). Having shown how the isotopic ratios of end products can be quantitatively related to those of their starting materials, we shall illustrate now how isotopic profiles of natural or chemical products can be interpreted in terms of the mechanistic routes of their elaboration. On this basis, it will be shown that the NMR method provides a very powerful tool for inferring the origin of molecules in terms of different properties of the precursors such as—the natural or chemical nature, the type of plant, the region of plant growing, possibly the year of production, the technological treatments, etc.

This text aims at presenting an account of the use of high resolution ^1H and ^13C Nuclear Magnetic Resonance (NMR) spectroscopy for the direct characterization of the composition of wine, beer, and spirits. This differs from the approach involved in the well established quality control method known as Site-specific Nuclear Isotope Fractionation (SNIF)-NMR, which usually involves ^2H observation for the measurement of isotopic ratios and correlation with product origin and which is described in a separate entry of this handbook. The application of high resolution NMR to the complex food mixtures mentioned above aims at detecting as many compounds as possible, including minor components, not only giving a compositional overview of the food, but also allowing the unexpected to be detected in a number of possible situations (biochemical studies, adulterations, contaminations). A vast number of studies have used NMR to identify particular compounds in sample extracts following specific separation and concentration steps. In wine, phenolic compounds are still the class of compounds more extensively studied due to their role in wine characteristics as well as interesting antimicrobial and antioxidant properties. However, the intention of this text is to account preferably for studies involving the direct NMR analysis of whole samples, rather than of their extracts, except where otherwise specified.

The applications of NMR to dairy products are numerous and can be divided into three groups. The first group comprises the use of high-resolution NMR spectroscopy for the molecular study of dairy compounds such as casein and whey protein [1,2]. The second group involves the use of Magnetic resonance imaging applied to dairy processing [3,4], and the third group concerns studies based on NMR relaxation measurements. This chapter will focus only on NMR relaxation applications, including pulsed field gradient NMR for the measurement of molecular diffusion. Relaxation measurements on dairy products have usually been performed at low field and the main aim was to propose a non-destructive technique to determine water or fat content [5] and solid fat content (SFC) [6]. These applications use NMR signal intensity and little attention has been paid to relaxation time values and their significance. We have therefore chosen to review this field of application specifically.

Characterization of molecular mobility in complex systems can provide much useful information that helps scientists understand various biological, chemical, and physical phenomena of a complex system. In this chapter, we will explore the applications of nuclear magnetic resonance (NMR) to determine molecular mobility of primarily cereal systems using multinuclei (proton, deuteron, and oxygen-17), carbon-13 solid-state NMR, proton cross relaxation (CR), and some application use in relation to microbial activity.

The main constituents of muscle and meat are water, protein, and fats, which represent approximately 75%, 18–20%, and 2–5%, respectively. Lean meat content and water-holding capacity (WHC) are of high interest to the meat industry as these are directly reflected in the payment of meat carcasses and the economic value of the meat during storage and further processing. Moreover, WHC and especially the distribution of the water within the meat are known to affect the sensory properties and the shelf life of meat. Consequently, measurement of lean meat content, WHC and water distribution in meat, and an understanding of intrinsic factors (e.g. species, genotype, muscle type), and technological processes (e.g. slaughter procedure, cooling regime, storage, processing) on water characteristics within the meat are of major importance for the meat industry. Especially noninvasive and non-destructive measuring techniques are demanded by the industry to control these important quality parameters.

The classic application of time-domain (TD-)NMR in food science and industry are devoted to products containing either a dominating amount of water or fat with the aim to determine the concentration or the amount of a specific component. The analysis result is commonly the fat content, in some examples also the moisture content. This is due to the fact that in TD-NMR almost no spectral resolution is available and that the transverse and longitudinal NMR relaxation properties of fat and water molecules are not substantially different. Moreover, the selectivity in commonly known TD-NMR pulse sequences is too small to guarantee a clear separation of signals. The classical approach was to pre-dry the samples either for example by an oven, chemical reagents like CuSO_4 or via infrared or microwave drying processes. The disadvantage of the pre-drying is clearly that it is a time-consuming method requiring labor time and rendering the TD-NMR application a two-step approach. Therefore, more elaborate experiments have to be examined in order to address these application questions on food products. Due to the technical development of the TD-NMR spectrometer, especially of the electronic part in recent years, also more sophisticated experiments can be implemented and run for quality control in food science and industry. In this paper the physical background and selected examples of new applications will be shown.

Although NMR is ubiquitously applied for chemical analysis and structural research as well as in its clinical adaptation of magnetic resonance imaging (MRI), its use in quality control/quality assurance (QC/QA) is often not very well known. It is this successful application field of NMR, which is dealt with in this contribution.