Citrus fruit is well known for its medicinal value. The go-to vitamin to fight off everything from the common cold to cancer is vitamin C. According to Harvard: “It is needed to make collagen, a fibrous protein in connective tissue that is weaved throughout various systems in the body: nervous, immune, bone, cartilage, blood, and others.” 
Flavonoids are a class of phytochemicals that can be found throughout all parts of citrus fruit. In a study by Addi, et al., they found the following flavonoids to be present: hesperidin, naringin, narirutin, naringenin, eriocitrin, and didymin/neoponcirin with hesperidin and naringin being the most abundant in the peel.  It is important to note that these flavonoids were present in different levels in different types of citrus fruits including (but not limited to) oranges, lemons, and grapefruits.
Specifically, citrus flavonoids carry a number of “therapeutic properties including antiallergenic, antiatherogenic, anti-inflammatory, antimicrobial, anticarcinogenic, antithrombotic, cardioprotective, and vasodilatory effects.” 
Studies have shown that dried citrus peels have a higher concentration of flavonoids than fresh. This was further shown by Castro-Vasquez, et al. They found an increase in the cytoprotective and antioxidant flavonoids in dried grapefruit peel. 
However, getting the value of these flavonoids requires extraction. Addi, et al. state, “Juice preparation and the processing of fresh Citrus fruits may decrease flavonoids content by 50% due to their water washing methods, or by elimination of the richest parts of the fruit.”  It is important to use the correct extraction methods.
There are numerous conventional extraction methods. However, Addi, et al. point out that these methods typically degrade the compounds that are being extracted. Thus, non-conventional techniques such as ultrasound assisted extraction (UAE) and supercritical fluid extraction (SFE) should be more utilized. 
The benefits to UAE include reduced extraction time and use of water as a solvent. The benefits of SFE include an increase in flavonoid production. Both extraction methods include the use of methanol as either a solvent or cosolvent. 
Utilizing the proper extraction methods to get the beneficial flavonoids from fruits and vegetables, especially the parts that are being disposed of has benefits to the health industry as well as reducing food waste. There are also impacts to our environment from releasing bioactive compounds including flavonoids into landfills and water bodies.
 Addi, M. Et al. An Overview of Bioactive Flavonoids from Citrus Fruits. Applied Sciences. 2022; 12, 29. Doi: https://doi.org/10.3390/app12010029. Times cited=0. Journal impact factor=2.679.
 Castro-Vasquez, L. Et al. Bioactive Flavonoids, Antioxidant Behaviour, and Cytoprotective Effects of Dried Grapefruit Peels (Citrus paradisi Macf.). Oxidative Medicine and Cellular Longevity. 2016; Jan 21. Doi: 10.1155/2016/8915729. Times cited=211. Journal Impact Factor=6.543.