**3. Bioactive compounds of** *Citrus* **fruits**

*Citrus* fruits are high in bioactive chemicals, particularly phenolic compounds (flavonoids, coumarins, and phenolic acids), terpenoids (carotenoids and limonoids), and pectin [3, 18, 19]. *Citrus* fruits are also high in nutrients, including ascorbic acid, tocotrienols, tocopherols, and minerals (iron, manganese, zinc, selenium, and copper) [3, 18, 19]. Flavonoids, which are a significant source of antioxidants in the diet of humans, are a kind of polyphenolic compound abundant in *Citrus* fruits. Flavanones account for approximately 95% of the total flavonoids generated by *Citrus* [20]. *Citrus*-derived flavonoids can be aglycones or glycosides, and they as a rule do not happen in nature as aglycones yet rather as glycosides, in which the aglycones are linked to a sugar molecule [21]. *Citrus* fruits contain a significant quantity of flavonols (kaempferol, quercetin, and rutin), polymethoxylated flavones (e.g., 5-dimethyl nobiletin, tangeritin, and nobiletin,), flavanone-7-O-glycosides (narirutin, naringin,

#### *Citrus Resea*rch - *Horticultural and Human Health Aspects*


#### **Table 1.**

*Nutritional characteristics for* Citrus *fruits per 100 g fruit [1].*

eriocitrin, and hesperidin), flavones (e.g., vitexin, diosmin, and rhoifolin,), and anthocyanin (peonidin glucosides and cyanidin) [22, 23]. When contrast to other *Citrus* species, *C. aurantium* has a higher concentration of active alkaloids, particularly synephrine, which accounts for more than 85% of the total alkaloid value [24]. The most common limonoids due to the dominance of *Citrus* species are limonin and limonin glucoside. Carotenoids are a type of isoprenoid pigment that is widely used in photosynthesis and signaling [24]. *Citrus* fruits' peel and pulp are orange-red owing to the existence of carotenoids and apocarotenoids [25]. *Citrus* fruits' carotenoid content is by carotenoid fatty acid esters (xanthophyll esters) [25, 26]. The bioactive compound of *Citrus* is presented in **Table 2** [1].

The existence of specific total carotenoids & xanthophyll esters is strongly impacted by species, maturation stage, and fruit components. Tangerines and oranges contain substantial amounts of β-cryptoxanthin, zeaxanthin Lutein, and β-carotene [27].


#### **Table 2.**

*Bioactive substance of* Citrus *fruits [1].*

The carotenoids found in the endocarp and flavedo of completely developed oranges were (all-E) and (9Z) violaxanthin, which were esters and monoesters containing myristate, palmitoleate, caprate, stearate, palmitate, oleate acyl moieties & laurate, lutein, β-carotene, and antheraxanthin were the other important carotenoids. In contrast, violaxanthin, β-carotene, α-carotene, and lutein were shown to be plentiful in ripe green fruit, furthermore, β-citraurin esters were discovered in *Citrus* fruit flavedo [28]. *Citrus* fruits' provitamin a carotenoids (e.g., β-cryptoxanthin) have also

been found to help with metabolic disorders, such as type 2 diabetes [29]. Hesperidin (HSP) is a potent bioactive flavonoid aglycone and subclass of flavonoids found in *Citrus* species (lime, orange, lemon, and blood orange) [30]. This flavanone has been demonstrated to have a variety of pharmacological actions, including antiviral activities, anticarcinogenic, anti-inflammatory, and antioxidant properties, analgesic [31], hypolipidemic, hypoglycemic activities, and anticoagulant [32].
