## 1 Introduction  
In the last two decades, compounds with antioxidant capacities have attracted increasing interest [1], in particular polyphenols, carotenoids and vitamins (mainly E and C). This specific attention derives from the ability of these compounds to scavenge free radicals and reactive oxygen species which are known to be involved in the development of cardiovascular diseases and several cancers [2]. Since one of the main sources of antioxidants are fruits and vegetables, these foodstuffs have gained great interest and widespread usage in the nutritional strategies applied to prevent these pathologies [2]. In this context, tomato (_Lycopersicon esculent_ L) and pepper (_Capsicum_ spp. ), both belonging to the _Solanaceae_ family, are considered to be important sources of natural carotenoids and phenols [3; 4]. Among vegetables, tomato, which is consumed either as raw fruit or as a processed product, is the second most important vegetable crop in the world and one of the main components of the Mediterranean diet [5]. Furthermore, the industrial processing of tomato leads to by-products, namely tomato seeds and peels, representing 10-40% of total processed tomatoes [6]. The management of tomato by-products is considered an important problem faced by tomato processing companies, as they cannot be discharged into the environment due to their high polluting potential [4]. The bioactive compounds present in industrial tomatoes and their processing by-products include tocopherols, polyphenols, carotenoids (mainly lycopene), some terpen, and sterols [7]. Thus, tomato wastes are a cheap resource to be recovered and recycled within the food chain, and a sustainable strategy able to address the current challenges of the industrialized world is required [8]. Besides tomato, red pepper (_Capsicum_ spp.) is also an important vegetable consumed worldwide. Due to their circulatory stimulant functions, chili peppers (_Capsicum annuum_ L.) are of ethnopharmaceutical importance and are also widely used as fresh fruits and savoury food additives due to their colour, pungency, and aroma [9; 10; 11]. Furthermore, the presence of many bioactive components such as vitamin C, phenolics and carotenoids [11; 12; 13; 14; 15; 16] makes peppers extremely attractive for the phytochemical manufacturing industry as well. In particular, among carotenoids, which increase in concentration greatly during pepper maturation [14], the most representative are \(\alpha\) and \(\beta\)-carotene, \(\beta\)-cryptoxanthin, capsanthin, lutein, and zeaxanthin [16]. The phenolic fraction includes mainly phenolic acids (cinnamic acid derivatives and hydroxy-substituted benzoic acids) and flavonoids (e.g., quercetin and luteolin) [10; 15]. In this context, the recovery of bioactive compounds (mainly carotenoids and polyphenols) from tomato wastes and peppers requires the use of mild extraction technologies, able to preserve the nutritional and pharmacological properties of these molecules, but also their antioxidant power [17; 18]. Conventional Solvent Extraction (CSE), such as organic solvent extraction, has been widely used to extract carotenoids and/or phenols from plant material. Traditionally, CSE used n-hexane, propanol, methanol, tetrahydrofuran or ethyl acetate to extract carotenoids. This method usually requires long extraction times, large amounts of organic solvents and high temperatures, which can lead to extensive degradation of thermo-sensible molecules, as well as leave trace amounts of potentially toxic solvents in the extract [17]. Moreover, the sustainability of the extraction process and the purification of the bioactive compounds is of the utmost importance [19]. Nowadays, supercritical fluid extraction (SFE) employing Sc-CO\({}_{2}\) is an established industrial process for the production of high added-value products. In 2014 there were more than 150 SFE industrial plants with a total extraction volume of more than 500 L in the world [19].