## 2 The NMR-Based Metabolomics in Food Science and the Foodomics Approach
### The NMR-Based Foodomics Approach for Food Bio-Waste or By-Products Analysis  
The majorization of the green aspects in the NMR-based foodomics leads to a green NMR-based foodomics approach [13], and it answers much more to the consumers \"2.0\" needs in terms of both food safety and quality, and sustainability. The green attribution has a twofold meaning: (1) green because, as it has been previously underlined, it involves \"environment-friendly\" chemicals (green chemistry). [PERSON], et al. [85] demonstrate how foodomics can emerge as a green discipline by applying the basic concepts of Green Chemistry; (2) it is green because its challenge is to preserve sustainability, understood as a way of using and preserving what nature gives us in the most productive, environmentally safe way [85]. In the last years, foodomics started dealing with food ingredients able to improve our health, which means nutrients and BC. Thus, the extraction of BC from natural sources (such as plants, algae, food bio-waste, and food by-products, among others) and the quality analysis of functional foods (FF) is a key step in the foodomics workflow [16; 85]. Food bio-waste or by-products from various sources can be fundamental for BC production and FF formulation. The high added value of these wastes is due to the content of BC, which, most of the time, is greater than in the edible part of the fruit [86]. For this reason, their proper waste management plays a vital role in the growth of food industries as they can contain valuable components such as polysaccharides, proteins, fats, fibers, and flavor compounds [87]. [PERSON], et al. [88], by using 1H NMR, described bioactive metabolites from pineapple waste. These compounds have antioxidant capacity and they can inhibit the activity of a carbohydrate-active enzyme (\(\alpha\)-glucosidase). In conclusion,it emerges that 3-methylglutaric acid, threonine, valine, and \(\alpha\)-linolenic acid were the main contributors to the antioxidant activities, whereas epicatechin was responsible for the \(\alpha\)-glucosidase inhibitory activity. The metabolic composition of cherimoya leaves (_Anmonia cherimola_ Mill.) is also characterized by the presence of BC, such as phenolic compounds. It is a deciduous tree from the Annonaceae family, typical of Peru and Ecuador, and its fruits are largely produced in Spain [86]. In this case, the metabolic composition has been profiled by using the 1H NMR coupled with high-performance liquid chromatography coupled with time-of-flight mass spectrometry (HPLC-TOF-MS). The first (1H NMR) achieved 23 primary compounds, classified as amino acids, organic acids, carbohydrates, choline, phenolic acid derivatives, and flavonoids. The second (HPLC-TOF-MS) profiled 66 secondary metabolites among carbohydrates, amino acids, phenolic acids and derivatives, flavonoids, phenylpropanoids, and other polar compounds [86]. Similar antioxidant proprieties have also been identified in pistachio's hard shells [89], blackcurrant skin [90], olive oil by-products [36; 37], and date palm by-products [91]. In this last case, a strong antioxidant activity has also been attributed to date fruits, whose bioactive metabolites have been profiled by 1H NMR by [PERSON], et al. [92]. In this work, five different cultivars have been compared to find the one with the most antioxidant activity. The obtained results demonstrated that the extract from the Piyarom variety had both the highest total phenolic and flavonoid content and exhibited good antioxidant activity. The metabolites responsible for the antioxidant activity, glucose, ascorbic acid, epicatechin, gallic acid, and citric acid, were successfully identified using 1H NMR-based metabolomics [92]. Among the BC, a particular interest is covered by prebiotics which are defined as \"a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health\" [93; 94].