**1. Introduction**

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> Nowadays, consumption of fruit and vegetable is very widespread as they provide health benefits. These benefits are partly due to the phenolic compounds that products contain. Phenolic compounds are plant secondary metabolites, with a structure composed of an aromatic ring linked to one or more hydroxyl substitutes. They are synthesized in the normal plant growth and reproduction and, also, during stress conditions such as high temperatures, hydric stress, ultraviolet radiation, or parasites [1]. These phytochemicals are bioactive molecules with antioxidant, antithrombotic, anti-inflammatory, and antidiabetic properties, among others [2–4]. Among phenolic compounds, simple phenols and polyphenols can be distinguished. The first group includes phenolic acids (benzoic and cinnamic acids) and benzoquinones, while flavonoids, stilbenes, lignans, tannins, and other polymerized compounds are part of polyphenols group.

> The current need of a sustainable food chain demands an implementation of a circular economy approach in the processing industries. The major focus of this approach is

**Citation:** López-Salas, L.; Borrás-Linares, I.; Quintin, D.; García-Gomez, P.; Giménez-Martínez, R.; Segura-Carretero, A.; Lozano-Sánchez, J. Artichoke By-Products as Natural Source of Phenolic Food Ingredient. *Appl. Sci.* **2021**, *11*, 3788. https://doi.org/10.3390/app11093788

Academic Editors: Luca Mazzoni and Hari Prasad Devkota

Received: 13 March 2021 Accepted: 19 April 2021 Published: 22 April 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

to revalorize the discarding parts of vegetables due to their grea<sup>t</sup> contents in bioactive compounds. This trend is supported by the potential of these food wastes, which could be used for the production of valued products. In fact, peels, seeds, stems, or vegetable pulps are considered raw materials to obtain bioactive ingredients with multiple applications, mainly for the production of food ingredients, cosmetics, or nutraceuticals. Furthermore, bioactive compounds of vegetable wastes have demonstrated antioxidant and antimicrobial actions in developed food additives used for conservative purposes. Its formulation in nutraceuticals with different presentations, such as syrups, capsules, pills or tablets, is very common [5,6]. These applications are possible due to the content in phytochemicals of these vegetable wastes with potent bioactive activities, such as phenolic compounds.

Artichoke (*Cynara scolymus* L.) is an herbaceous perennial plant belonging to *Cynara* genus and Asteraceae family. Commonly known as globe artichoke, it is traditionally consumed in the Mediterranean diet in different popular preparations. It can be consumed fresh, canned, roasted, or baked, among others. Therefore, this vegetable is extensively cultivated in Mediterranean countries such as Italy, France, Spain, Egypt, and Morocco. Their cultivation is considered an important activity of the agro-economy of these countries [7,8], indeed, the Mediterranean region has an annual production of about 770,000 tons. The edible portion of this plant includes the receptacle of immature flowers and the inner bracts, named "capitula" or heads. During the artichoke processing, the residues, principally external leaves or stems, represent approximately 60–80% of the total harvested plant material, which is translated in more than 460,000 tons of wastes generated annually. Nevertheless, these by-products possess a grea<sup>t</sup> content of bioactive phenolic compounds, inulin, fibers, and minerals [9–13]. This information highlighted the significance of the evaluation of artichoke wastes for the extraction of bioactive compounds.

The artichoke is one of the most consumed plants of its genus due to its high nutritional value, being rich in water, minerals, vitamins, and carotenoids. Despite its content in these interesting compounds, it is the presence of bioactive compounds that has aroused greater interest, especially phenolic compounds [14,15]. The interest in their phytochemicals has been linked to various pharmacological activities exerted on humans. Thus, hepatoprotective, antioxidant, hypocholesterolemic, anticarcinogenic, antibacterial, or diuretic effects have been described for artichoke. Therefore, the artichoke has been used for medicinal purposes since antiquity, being considered a functional food [9,10,16,17].

Consequently, the re-valorization of food by-products as a bioactive source material has experienced a grea<sup>t</sup> growth due to the economic and environmental benefits that it produces. In the case of artichoke, recent studies based their research on external bracts, leaves and floral stems by-products, which are considered the principal discarding parts of the artichoke processing because they are not suitable for human consumption [18].

The main objective of this article was to explore the potential of artichoke by-products generated in the food industry as a green and efficient source of phytochemicals with many applications. For this purpose, the present research optimized the extraction of the phenolic profile from artichoke bracts and stems, which were obtained as industrial by-products, through an advanced extraction system and characterized the composition of the obtained extracts by a powerful analytical platform. Thus, pressurized liquid extraction (PLE) using water and ethanol as GRAS extraction solvents was chosen due to its grea<sup>t</sup> potential to extract phenolic compounds in green and efficient processes from vegetable matrices. Similarly, reversed-phase high-performance liquid chromatography coupled to electrospray time-of-flight mass spectrometry (HPLC-ESI-TOF-MS) was selected for the analytical characterization of the PLE extracts due to its grea<sup>t</sup> potential.

### **2. Materials and Methods**
