# Antioxidant and Potentially Anti-Inflammatory Properties in Pasta Fortified with Onion Skin
## 1 Introduction  
Onion (_Allium cpa_ L.) is the most widely cultivated species of the genus _Allium_, and the second (after tomatoes) most important horticultural crop worldwide. Current annual production is about 88 million tons, and the largest producer is Asia (55 million). Less than 10 million tons of onion is produced in Europe, where Poland is the third largest producer, with a yield amounting to 660 thousand tons in 2018 [1]. A commonly used part of onion is the bulb, which is a raw material or food ingredient, because of its specific flavor and pungent smell [2]. Numerous studies have confirmed the pro-health activities of onion by in vitro and in animal model tests, in particular, antioxidant, antibacterial, antifungal, cardio-protective, anti-inflammatory, anti-carcinogenic, anti-obesity properties,and the promotion of glycemic control [3; 4]. These features are attributed to bioactive compounds, among which phenolic compounds, including phenolic acids and flavonoids, constitute a large group (mainly quercetin diplucoside, quercetin 4'-glucose, quercetin aglycone, isorhamtein monoglycoside, and kaempfer monoglycoside), phenolic acids (ferulic, \(p\)-coumaric, gallic, 3,\(A\)-dihydroxybenzoic), sulphur compounds, and non-structural carbohydrates. Concentrations of these compounds depend on cultivar, stage of ripeness, environment and agronomic conditions, storage time, and, in addition, the bulb section (inner, outer scales or dry skin) [5; 6; 7]. During the processing of onions, about 30% of fresh material is removed and considered useless waste, which includes dry skin [8]. These wastes are an ecological and economic problem, and the main difficulty in their management is their heterogeneous character. The composition of the onion waste varies depending upon the morphological part of the bulb. Therefore, a common strategy for all of them cannot be adopted [9]. A possible solution to use dry onion skin could be to use it as a source of valuable food ingredients such as insoluble dietary fiber, minerals (especially calcium and potassium), and highly bio-accessible and in vitro bioavailable flavonoids with well-documented antioxidant and anti-inflammatory abilities [10; 11; 12; 13]. Literature data suggests taking into account the utilization of onion skin as a valuable by-product in the food processing industry [14; 15], especially since the bioactive components of the flavonoid group are relatively thermally resistant. In recent years, dry onion skin has been used to design functional or enriched foods, such as pasta [16; 17], noodles [18], bread [19], extruded products [20], and yoghurt [21]. In addition, the use of dry onion skin has also been considered as a raw material for the health industry for medicines and pharmaceuticals [11] and in the textile industry [22]. Studies focusing on the effects of different plant components in addition to food products suggest that among various assortments of cereal products, pasta is especially suitable as a carrier of bioactive substances. Pasta is one of the most popular convenience food in the world for its easy preparation, nutritional value, and palatability [23]. Due to the fact that fruit and vegetable by-products contain bioactive compounds with significant biological activity, they are of interest to international researchers. Over the last few years, numerous studies have considered the possibility of incorporation of by-product extracts or powders for preservation or enrichment of food products. This is associated with current interest of consumers, who are demanding the production of safer and health-promoting foods [24]. Currently, pasta is fortified with by-products such as mango peel [25], tomato skin [26], outer bracts, leaves, stems of artichoke [27], cereal brans [28], bean flour [29], olive oil industrial by-product [30], beef meat [31], and shitake and porcini [32]. Therefore, such pasta is considered to be a \"convenient food with a high pro-health potential for future generations\" [23].