In addition to vitamin A, C and potassium, watermelon (Citrullus lanatus) also contains lycopene, citrulline, and arginine. Lycopene is the pigment that imparts redcolor to some fruits, most notably tomato and watermelon. It is also a highly efficient oxygen radical scavenger and has been implicated in human studies as providing protection against cardiovascular disease and some cancers, particularly that of the prostate. Watermelons contain as much or more lycopene than tomatoes but have been little studied. Over the last six years, we have conducted numerous studies with watermelon to evaluate germplasm, storage and minimal processing effects on lycopene levels. Additionally, we conducted a cooperative human clinical study with watermelon and tomato juice to determine lycopene uptake in humans. Assays of human plasma after watermelon ingestion indicated that lycopene was as bioavailable from watermelon juice as from tomato juice. Citrulline and arginine are amino acids found in watermelon and are major components of the human nitrous oxide system and help regulate many biochemical processes. Citrulline lacks biological importance on its own but is transformed by the human body into arginine. Arginine is used in the nitric oxide pathway to help in vasodilatation and overall cardiovascular health. Our recent work with citrulline identified that it is present in watermelons in the peel, rind, and flesh. Following the lycopene human clinical trial we measured the citrulline levels in the human plasma from the subjects who ingested watermelon juice. Plasma levels of citrulline were highest in subjects who consumed six cups of watermelon juice per day. Further studies with these unique compounds found in watermelon are ongoing.
