## 3 Bioactive Compounds of _Citrus_ Seeds
### Phenolic Compounds  
Phenolic acid is composed of a phenolic ring joined to a carboxylic ring, thus forming a C6-C1 molecular structure. The total phenolic content (TPC) of _Citrus_ seeds varies widely among species, ranging from 1.2 mg gallic acid equivalents (GAE)/g dry weigh (DW) for lemon to 2.5 mg GAE/g DW for bitter orange [17]. C. _medica_ L. seeds have a significantly higher TPC of 0.7136 mg GAE/g DW [39]. Sprouts can significantly increase the TPC, with sprouts showing values between 6.8 mg GAE/g DW for lemon and 11.2 mg GAE/g DW for blood sweet orange. Moreover, the internal waste parts of _Citrus_ fruits, including seeds, show a TPC range of 16.2 to 19.2 mg GAE/g DW, indicating their potential as a source of valuable phenolic compounds [40]. Mandarins were found to have a TPC ranging from 0.07537 to 0.09136 mg GAE/g in a study examining the TPC of _Citrus_ seeds. Oranges showed a wider variability with TPC ranging from 0.04663 to 0.08866 mg GAE/g DW, reflecting differences influenced by environmental factors. For lemonas, a similar TPC range of 0.07716 to 0.09261 mg GAE/g DW was observed, with some reports indicating a total of 0.17283 to 0.19429 mg GAE/g DW [41]. Yet, another study established a range of TPC 14.51 mg of GAE/g for _Citrus limon_ v. Eureka [27]. The TPC of _Citrus_ seeds is influenced by the extraction methods. For example, oils extracted from _Citrus_ seeds have different TPC depending on the extraction technique used, with values ranging from 0.682 to 0.932 mg GAE/g oil. The highest TPC was observed in sweet orange seed oil extracted by solvent extraction, which reached 0.932 mg GAE/g oil [33]. In a further study, the highest TPC was found in Kinnow mandarin with 158.2 mg GAE/g DW, followed by Orlendo orange and Eureka lemon with 113 mg each. The optimization of post-harvest procedures is critical to increase phenolic recovery from seed biowaste and to overcome this variability [1]. Compared to other nutrient components of seeds, polyphenols contribute most to the _Citrus_ seed's antioxidant activity. Some of their benefits include antioxidant, anticarcinogenic, and anti-inflammatory properties, and they are beneficial in treating cardiovascular disease, diabetes, and neurodegenerative disorders [42]. Phenolic acids (gallic acid and trans-ferulic acid) were significantly higher in the cold-pressed lemonseed oils [43]. Other authors compared three different varieties of _Citrus_ oil seeds. Lemon seed oil was found to have the highest total phenolic content level (82.02 mg GA/kg seed), followed by mandarin and orange (80.93 mg GA/kg seed and 78.43 mg GA/kg seed) [41]. In the _Citrus_ genus, flavonoids are divided into three main groups: flavanones (naringin, naringinin, hesperidin, heespretin), polymethoxylated flavones (nobilitin and tangeritin), and flavonoid glycosides (rutin). These compounds in _Citrus_ exhibit strong antiinflammatory properties [44]. Much research has been conducted regarding the biological effects of grapefruit flavonoids, such as naringin on the components of the metabolic syndrome, including hyperglycemia, hypertension, insulin resistance, and obesity [45; 46]. Naringin is a major flavonoid in grapefruit and sour orange, which contains a glucose moiety that provides it a bitter taste. Various _Citrus_ species, including sweet orange, tangelo, lemon, and lime, possess low levels of naringin [44]. It is also possible to attribute the difference in naringin content to fruit maturity, as well as grapefruit varieties [45]. Moreover, grapefruit seed oil contains hesperidin/neohesperidin, which have several biological activities. It was also demonstrated that orange seeds are extremely rich in hesperidin (40 g/kg) [47]. In conclusion, the _Citrus_ family contains a great deal of polyphenols Table 1.