In addition to vitamin C and the terpene limonene which gives citrus its characteristic scent, citrus peel contains many beneficial flavonoids including quercetin and hesperidin. The bitter taste of some of the phytonutrients helps health in many ways throughout the body.
The group of bitter taste receptors can perform functions besides perceiving taste sensations on the tongue. Bitter tasting nutrients or medicines can activate taste receptors in other parts of the body that cause different functions depending on the cell and tissue. In lung tissue airways open, mucus production increases and is thinned with more fluid and cilia move it up and out - protection against inhaling irritants that are bitter possibly. Within the digestive and circulatory system bitter taste receptors help with blood sugar control, decrease appetite and may help with weight control. Use of citrus bioflavonoids are being studied for asthma treatment, and for Metabolic Syndrome. See: Bitter taste receptors in the lungs & Hesperidin's decongestant properties.
The inner pith of citrus peel is mild in flavor compared to the outer zest layer. Medicinally also the pith is less potent, more would be needed to provide the same amount of bitter taste receptor activation. The amount needed to clear congestion and asthma symptoms for a few hours might be 1/2-one Navel orange with the white pith left on the orange wedges or about one to two teaspoons of the outer zest minced and added as a fresh garnish on soup or salad. Citrus peel is also used as a jam or chutney or in candied citrus peel for baking or dipping in chocolate. (Citrus and other fruit peel jam recipes) (Hesperidin and Quercetin content in Citrus peel.)
Dried lime or lemon powder is available in Middle Eastern markets and might be in canisters for sprinkling on at the table or as whole dried limes.
Tangerine peel is dried for a Traditional Chinese Medicinal herb called Chinpi. It might be made into a tea along with a few other herbs in a blend for respiratory or digestive conditions. Citrus peel tea, water extract of chinpi, has been found beneficial for remyelinating nerves which can be a degenerative problem with few known treatments. (1)
Hesperidin has been studied for a variety of health conditions and may be helpful as a prevention or treatment for COVID-19 infection. "Hesperidin can block coronavirus from entering host cells through ACE2 receptors which can prevent the infection." (2) Chinpi is a recommended treatment for the non-productive cough stage of CoV-19 in Chinese health guidance for individuals or practitioners. (3)
More about the role of ACE2 receptors inCOVID-19infection is available in this post along with foods that may help with diarrhea and inflammatory bowel symptoms. (ACE2, Diarrhea, & COVID19 – it gets complicated.)
Quercetin may also have antiviral benefits as a zinc ionophore. Zinc is also an essential trace mineral involved in gene transcription of the protein that forms taste receptors. Lack of sense of smell and taste can be a symptom of zinc deficiency and can be a symptom of COVID19. Older adults may need more zinc then the standard recommendation in order to promote thymus gland function - necessary to make antibodies.