Naringin is the principal flavonoid constituent of grapefruit. Because of its extreme bitterness, naringin when present in excessive amounts is considered to be a prime factor in limiting the acceptance of grapefruit. The presence of naringin in grapefruit has been known for many years, and its physical and chemical characteristics have been well established, but the knowledge of the biosynthesis of naringin in grape fruit is very limited. Although a general working hypothesis for the pathway of naringin biosynthesis can be deduced from radiotracer studies of phenolic biosynthesis in other plants and from knowledge of the phe nolic constituents found in grapefruit, most of these steps have not been demonstrated in grapefruit. Even more important, the enzymes catalyzing each of these steps in the deduced pathway have not been demonstrated in grapefruit.
Because our main objective is to learn what controls naringin production and accumulation in the fruit, studies have been undertaken to determine what enzymes are involved in the biosynthetic pathway, to meas ure the activities of the enzymes and to correlate their activities with the rate of naringin accumulation.