¹H High-Resolution Nuclear Magnetic Resonance (¹H HR-NMR) spectroscopy is a versatile analytical methodology that exploits the magnetic properties of certain atomic nuclei. It has widespread applications in different scientific areas, such as chemistry ^[1], biochemistry ^[2][3], medicine ^[4][5][6], and materials science ^[7]. In recent decades, this methodology has also been largely used in the fields of health, environment, and food science, with a high amount of research papers produced ^[8][9][10]. In these fields, the nuclear methodology is often combined with the principles of metabolomics ^[11], where the metabolic profile of a biological system (e.g., cells, tissues, or biofluids) is studied. The so-called NMR-based metabolomics approach helps in identifying and quantifying small molecules, providing insights into metabolic pathways and changes in response to various external conditions ^[12]. NMR-based metabolomics has several unique advantages over other metabolomics techniques such as gas chromatography (GC) and mass spectrometry (MS), which is why it is increasingly being adopted in various fields. First of all, it is a more uniform detection system and can be used directly for the identification and quantification of metabolites, even in vivo ^[11]. Its non-destructive nature, relatively short times, and ability to measure samples such as urine directly are the most promising features of NMR. Another major advantage of NMR is the ease of quantifying all compounds, since a single internal standard can quantify all degraded metabolites without requiring calibration curves for each compound. Finally, the NMR specimen needs no physical or chemical treatment before analysis, only the adjustment of solution conditions such as temperature, pH, and salt concentration ^[11]. In the latter case, general sample preparation (biological or food) involves three basic steps: (1) The first step involves rapid sample collection and freezing to quench metabolism and preserve metabolites. Samples are typically stored at −80 °C to avoid degradation. (2) The second step involves extracting methods. The choice of extraction method depends on the function and the polarity of the metabolites to be extracted. If both polar and lipophilic metabolites are to be extracted, methanol and chloroform extraction can be used to separate metabolite classes. (3) Optimization of the solution for NMR spectroscopy is the third step. This typically involves buffering the pH of the sample to minimize chemical shift variation of the NMR resonance (e.g., 100 mM phosphate buffer, pH = 7.00), adding deuterium oxide (D₂O) to provide frequency locking to the spectrometer, and adding an internal chemical shift (and intensity) standard such as sodium 3-(trimethylsilyl)propionate 2,2,3,3-d4 (TSP) ^[11]. In food science, the NMR-based metabolomics approach is also known as Foodomics ^[13]. It can be employed for several applications which include, above all, analyzing the composition and measuring the physicochemical properties and functionality of food matrices ^[9]. Laghi et al. ^[13] clearly explain the reason why, in several areas of the food industry and food science, a Foodomics approach can be adopted, and the main reason is that the metabolome can be considered the last step of the omics pathway, which includes the genome, transcriptome, and proteome. Thus, it is the best representation of a food’s phenotype, providing a significant view of all the metabolites that may have an effect on or interact with the organism ^[13]. There is another important aspect that can and must be taken into consideration when dealing with NMR spectroscopy in the Foodomics field: it can be employed for the evaluation of the stability, quality, authenticity, and shelf life of food samples. This is highly important based on the increased demand from consumers for high-quality foods, quality that should be guaranteed during the period between purchase and consumption ^[14]. In the narrative review by Ciampa et al. ^[8], the authors perfectly explain the advantages of using ¹H-NMR metabolomics in food quality determination compared to other traditional methods, and why the food industry should pay attention to this emerging approach. First, the NMR method can assess and guarantee the quality of foodstuff through its capability to offer qualitative, as well as quantitative, knowledge about food samples, with high reproducibility. At the same time, compared with the other methods, it is more green, as it operates following the green chemistry guidelines for sample preparation ^[8]. NMR provides direct, non-destructive information on sample composition and concentration with confidence. Due to (1) the low cost per sample, (2) minimal sample preparation, (3) the simultaneous identification and quantification of compounds, (4) the combination of targeted and non-targeted analysis to ensure the presence of intended ingredients and the absence of impurities or adulterants, and (5) the advanced statistical models available to assess authenticity of origin, species purity, adulteration, production process control, sample similarity, etc., NMR is becoming a strategic tool for industries to assess and ensure food safety and quality to avoid fraud, contamination, adulteration, etc. Thus, this entry aims to give a summary and an overview of the applications of one-dimensional (1D) ¹H HR-NMR in the field of food quality analysis, also including food stability, authenticity, and shelf life, exploring, above all, two of the most used approaches in the food science field.

This entry is adapted from the peer-reviewed paper 10.3390/encyclopedia4040106