# A Review on Bioactive Compounds and Pharmacological Activities of _Citrus unshiu_
## 1 Introduction  
Citrus fruits, including lemons (_C. limon_), limes (_C. aurantiglia_), sweet oranges (_C. sinensis_), sour oranges (_C. aurantitium_), grapre fruits (_C. paradisi_), and others, are flowering plants with different sizes and forms, which belong to the genus _Citrus_ in the family Rucaceae [1]. These citrus fruits have been recognized as the most crucial for improving human health because they are a major source of vital nutrients and energy [1]. Citrus fruits are acknowledged for their anticancer, antioxidant, and anti-inflammatory activities due to the high levels of phytochemicals present in various parts of the plant, including the peels, seeds, and pulps [1, 2, 3, 4, 5]. The Satsuma mandarin, also called _Citrus unshiu_ Marc. (_C. unshiu_), is unique among mandarins due to its high flavor, seedless nature, highest total phenolic content, antioxidant potential, and significant amounts of fragrance compounds [7]. About 50-60% of the entire fruit mass is made up of citrus peels (albedo and flavedo), seeds, and pulps, which are acquired as byproducts (citrus wastes) during the processing of citrus fruits [8]. The albedo is the internal white layer of the peel that contains pectin, vitamins, and flavanones (e.g., narirutin, hesperidin). The flavedo is the peel's outer layer, which is rich in triterpenoids, pigments, steroids, and essential oils. Seeds are rich in fiber, crude protein, lipids, and nitrogen-free extract. Pulps mainly consist of organic acids, insoluble fiber, glucose, and fructose. The chemical constituents of citrus fruits and their byproducts are influenced by several factors, including extraction techniques/mode, storage period, cultivation method, stage of ripeness, and harvesting time [9; 10; 11; 12; 13]. Citrus flavonoids have low intestinal absorption, which has been linked to poor bioavailability in a number of experiments [14]. An in vivo experiment has shown a large amount of carotenoid \(\beta\)-cryptoxanthin (\(\beta\)CX) absorbed and stored in different rat tissues (liver, brain, heart, lung, spleen, kidney, testis) following administration of a standard diet containing C. _unshiu_[15]. A large body of evidence indicates that citrus essential oils used in cosmetic products are safe [16; 17]. However, essential oils isolated from citrus fruits (e.g., grapefruit, bergamot) demonstrated cytotoxic effects against various cancers [16; 18]. In vitro and in vivo experimental evidence indicates that C. _unshiu_ peel exhibits no genotoxicity and minimal systemic toxicity [19]. A clinical investigation revealed that overweight or obese individuals can safely use _C. unshiu_ peel pellets to improve their weight loss and lower their cholesterol and triglyceride levels [20]. According to a randomized placebo-controlled study, patients with periodital wrinkles who received a safe dosage of green mandarin extract containing narirutin (300 mg/day) for 12 weeks had an improvement in skin roughness in comparison to those in the placebo group (no green mandarin extract) [21]. Experimental evidence shows that lemon (_C. limon_) and sweet orange (_C. sinensis_) bioactives (e.g., limonene, terpenes, hespeden, naringin, daidzin, \(\beta\)CX) exerted various medicinal properties, including anti-diabetic, anti-obesity, and anticancer, through modulating signaling pathways as the mechanisms for these activities [22; 23; 24]. However, there has not been much focus on the pharmacological properties and mechanisms of action of _C. unshiu_ bioactives. The main bioactive compounds found in _C. unshiu_, together with their therapeutic properties, have not, as far as we are aware, been reviewed. This paper thus provides a summary of studies currently available on the pharmacological properties, bioactive compounds, and therapeutic mechanisms of Satsuma mandarin (_C. unshiu_). This review made the assumption that _C. unshiu_ is a significant source of many classes of bioactive compounds that, through various mechanisms of action, exhibit pharmacological activities in both in vitro and in vivo experiments.