## 2 Results and Discussion
### Analysis of Non-Volatile Resins  
Some flavonoid derivatives in citrus are specific. In this study, the components of citrus oleoresin extracted with SFE were analyzed by high performance liquid chromatography (HPLC), but phenolic acid and flavonoid aglycone were not detected. SFE cannot extract polar compounds; thus, polymethoxyflavone (PMF) could be detected in this study because of its lipophilic properties (Figure 1). In contrast, some related studies have reported that the PMF in the citrus oil of fortified commercial citrus juice cannot be detected [30; 31]. The literature reported finding rich flavonoids in the Taiwan citrus peel, and hesperidin was the most prevalent of these, with Ponkan and Tonkan peels containing 29.5 and 23.4 mg/g dry powder, respectively [32]. In this study, the identified flavonoids were tangeritin and nobilentin. Tangeritin and nobilentin both have many methoxy groups. The bioactivities of PMF, such as anti-inflammation, anticancer, anti-atherosclerosis, anti-virus, and anti-oxidative activities, are better than those of citrus flavonoids [33; 34; 35]. The tangeritin levels in Ponkan oleoresin, Tankan oleoresin, and Murcott oleoresin found in this study were 64.12, 54.19, and 24.05 mg/g. The nobilentin levels in Ponkan oleoresin, Tankan oleoresin, and Murcott oleoresin found in this study were 195.45, 99.31, and 62.23 mg/g. Citrus fruits contain abundant levels of phytosterols and limonoids, which have been identified to have many physiological functions. Limonoids have antibacterial, antipyretic, antimalarial, anticancer, and antiviral properties, in addition to begin able to promote glutathione S-transferase activity in liver and small intestinal mucosa [36]. Limonoids can be lactonized by the action of enzymes, giving them a slightly bitter taste [36]. The results of this study of citrus oleoresin extracted by SFE found that the samples were rich in limonoids, with the limonin levels in the Ponkan, Tankan, and Murcott being 71.17, 316.02, and 117.83 mg/g and the nomilin contents being 41.53, 90.24, and 130.47 mg/g, respectively. The Ponkan contained the highest amount of limonoids (Table 2). The pertinent literature has demonstrated that phytosterols have anti-inflammatory, anticancer, and antibacterial properties. Moreover, phytosterols can affect the structure of cell membranes and host organizations, including via the message pathway involved in the regulation of tumor growth and differentiation, in order to inhibit the growth of cancer cells [37]. Related studies have shown that citrus peel is a good source of phytosterols (23.4-32.6 mg/100 g dry powder) [38]. In this study, the total phytosterol level was the highest in the Murcott oleoresin (1216.42 ug/g), with the levels for the Ponkan and Tankan oleoresin being 985.54 and 876.88 ug/g, respectively (Table 2). The analysis results identified four kinds of phytosterols in the citrus oleoresin extracted via SFE. The Ponkan oleoresin contained campesterol (304.77 ug/g) and stigmasterol (680.67 ug/g); the Tankan oleoresin contained campesterol (211.61 ug/g), stigmasterol (131.82 ug/g), lanosterol (189.33 ug/g), and fucosterol (153.34 ug/g); and the Murcott oleoresin contained campesterol (455.54 ug/g), stigmasterol (374.17 ug/g), and fucosterol (486.71 ug/g).