## 2 The NMR-Based Metabolomics in Food Science and the Foodomics Approach
### The NMR-Based Foodomics Approach for the Simulated Digestion and Absorption of Food  
Food is a biological matrix where different food components are organized in a complex structure and interact with each other. The digestion process is needed to break the structure to release nutrients and other BC. Thus, the overall nutritional value of food and bioactivity of its components relies on the bioavailability, not only on the amount of both nutrients and BC [109]. Their bioavailability depends on several factors, including their bioaccessibility, which means the amount that can be released from the matrix during digestion and pass into the soluble fraction, becoming available for absorption. The composition of the food matrix and the processing which foods are subjected can influence digestion and, in turn, the bioaccessibility of its components. From this point of view, the evaluation of the in vitro digestibility of different food matrices subjected to different types of processing or transformation, for example, enriched with BC from by-products, represents a fundamental parameter for the determination of the nutritional value of foods, and the possible effect of nutrients and BC [110; 111; 112; 113]. NMR-based metabolomics showed a fundamental role in the determination of both the bioavailability and bioaccessibility of BC in natural or enriched foods during simulated digestion and absorption. The application of NMR methodology in this field respects the aim described in pillar 1: both the in vitro digestion and NMR analysis follow the green chemistry guidelines in sample preparation [109]. For the NMR, samples taken during digestion are prepared by adding to 1 mL of each sample, 160 \(\mu\)L of 1 m phosphate buffer in deuterium oxide (D2O), containing 10 mm 3-TSP as internal standard. According to the evaluation of the bioaccessibility of BC, a work by [PERSON], et al. [114] demonstrated how it depends on several conditions, such as (1) digestion conditions (pH, enzyme concentration, and activity), (2) compound stability, and (3) interactions with other food components, as well as the supramolecular organization of the food molecules [115]. In particular, the work focused on the effect of pH on the solubility and bioaccessibility of carnosine obtained by the digestion of bresaola, a typical beef-based product of northern Italy (Valtellina) [114]. Carmosine is a water-soluble dipeptide with functional and biological properties, especially as an antioxidant [116]. The dependence of BC bioaccessibility and bioavailability from the supramolecular organization of molecules in food, in summary, the food matrix, is also well described by [PERSON], et al. [117]. The research paper described the effect of inulin on the bioaccessibility and bioavailability of BC naturally present in acerola juice by applying both in vitro digestion and NMR protocols. After inulin addition, the prebiotic juice and a non-prebiotic one were first treated by to two different thermal processes and then subjected to in vitro digestion to evaluate the bioactive juice compounds' bioaccessibility and the juice composition. Inulin, beyond its prebiotic proprieties, also has a protective effect in preserving the organic compounds after industrial processes such as thermal processing, and also improving the bioaccessibility of BC in the treated juice [117]. The combination of in vitro digestion and 1H NMR has also been developed and employed in a work by [PERSON], et al. [118], where the first aim of the paper was the study of the hydrophilic metabolites of raw and cooked sea bass (_Dicentrachus labrax_) through NMR. First of all, the spectrometry technique has been used for both metabolites' identification and quantification, as well as to evaluate the effect of microwave cooking on them.