Citrus Flavonoids: A Review of Past Biological Activity Against Disease

Abstract

Flavonoids are common in fruits and vegetables and many function as natural antioxidants, free radical scavengers, and may also chelate pro-oxidant metals, reducing their capacity to produce free radicals (Affany et al., 1987). It has been estimated that humans consume 1 gram per day of flavonoids (Kuhnau et al., 1976). The majority of citrus flavonoids are flavanones bound as glycosides (Figure 1). Hesperidin, a glycoside of hesperetin, is predominant in orange and tangerine, whereas naringin and narirutin, glycosides of naringenin, are most abundant in grapefruit. Eriocitrin and hesperidin are the predominate flavonoids found in lemon and lime. Some therapeutic effects have been reported for citrus flavanoids (Fisher et al., 1982). In 1936 citrus flavonoids were reported to decrease capillary fragility and improve blood flow and were actually labeled “Vitamin P” (Rusznyak and Szent-Gyorgyi, 1936). But further research failed to substantiate that abnormal capillary permeability was due to a deficiency in bioflavonoids. In 1950, the Federation of American Societies for Experimental Biology recommended that the term “Vitamin P”, which had been applied to flavanoids, be discontinued (Vickery et al., 1950).