# Role of Quercetin in Depressive-Like Behaviors: Findings from Animal Models
## 3 Quercetin  
Fruits and vegetables thanks to their flavonoid content, acquired considerable scientific interest. The flavonoid content in fruit and vegetables is influenced by several pre-harvest factors, such as crop variations, climatic conditions, growing locations, agronomic factors, and harvest factors, such as maturity stage [50; 51; 52]. It has shown that in onions, rich in flavonoids (quercetin), the content of these compounds vary according to the cultivation as well as within its layers. Indeed, it has reported that the onion's dry peel shows a total phenols content 100 times higher than the bulbs and stems [50]. Environmental factors such as solar radiation, temperature variation and climatic conditions modify the flavonoid content in fruits and vegetables. Indeed, some researchers observed that solar radiation during the growing period significantly increases the quercetin content (from 1.43 to 8.1 mg/100 g fresh weight) [53]. Furthermore, solar radiation in the onion bulb increased the quercetin concentration from 10 to 50 mg/100 g fresh weight during the last growth phase [54]. Furthermore, the location and soil type represent important factors that change quercetin concentrations [55]. The ripeness stage can also influence the level of phytocompounds. In onions, an early lifting time results in low germination and a reduced level of quercetin [54]. However, in addition to these pre-harvest factors, several post-harvest phases affect the content of these phytocompounds within fruits and vegetables. Conventional transformation processes such as high-pressure pulsed electric field, ultrasound/sonication, ozone, ultraviolet, and processes such as washing, peeling, cutting, canning, and drying are known to degrade flavonoid content [56; 57; 58]. Microwave in the onions induces a 16-18% reduction in the glycoside content of quercetin [59]. Peeling in the onions also caused a reduction in 79% quercetin glycosides [60]. Similarly, a 60-min boil causes a reduction of about 44-53% [59]. Therefore, the development of new pre- and post-technology collections, could be important to improve the accumulation of phytocompounds in fruit and vegetables. Flavonoids belong to the large family of low molecular weight phenols which, based on their molecular structures, are divided into flavones, flavanones, isoflav, isoflavons, pterocarpans, counstemans, anthocyanins, flavanols (or catechins), and flavonoids [61; 62]. Among these flavonoids such as kaempeferol, quercetin and myricetin, are the most represented flavonoids thanks to their functional properties [63]. Fruits and vegetables (e.g., onions, apples, tea and berries, peppers cranberries, apples, cherries, and grapes) contain a high content of quercetin in the glycone or carbohydrate conjugates form. Indeed, the major quercetin-dietary intake consists of quercetin glycosides, a molecular of quercetin conjugates with one or two glucose residues or with routine. Interestingly, the growing conditions influence the amount of quercetin in food, indeed, compared to organically grown, conventionally cultivated tomatoes contained a lower amount of quercetin aglycone [64]. Quercetin is an abundantly represented source in the daily diet. It has been estimated that the daily intake of quercetin is around 5-40 mg. Instead, when quercetin took as a food supplement, the recommended do e is 200-1200 mg [65]. Quercetin belongs to the flavonoids family and owns 3-hydroxyflavone backbone (Figure 2). Quercetin is a powerful antioxidant, due to the catechol group and the hydroxyl group present in the molecular structure which confers it's an optimal conformation useful as a scavenger of free radicals [66]. Indeed, this flavonoid is a powerful inhibitor of lipid peroxidation, by reducing both cyclooxygenase and lipoxygenase activity. This is responsible for reducing the formation of inflammatory metabolites [67; 68; 69]. Furthermore, quercetin is also responsible for increasing antioxidant enzymes, preventing the formation of free radicals [70].