The same sugar that makes watermelon a sweet treat also may be a stock for producing ethanol.
And it's in no short supply, either. In 2007, about 800 million pounds—or 20 percent of the crop—were left in the field because of blemishes or because the fruit was a seeded pollinizer for a seedless variety.
Biofuel typically is produced from cane crops, such as corn, sorghum or sugarcane.
Chemist Wayne Fish's ethanol studies at the Agricultural Research Service's laboratory in Lane, Okla., complement ongoing research to commercially extract lycopene and citrulline from the crop, according to a news release.
The researcher showed that ethanol can be fermented from the glucose, fructose and sucrose in waste-stream juices—what's left after lycopene and citrulline are extracted.
Making ethanol offers the potential benefits of helping to defray sewage treatment costs of nutraceutical extraction and providing growers with a new market.
An average 20-pound watermelon will yield about 1.4 pounds of sugar from the flesh and rind, from which about 0.7 pound of ethanol can be derived.
To extract all the sugars, Fish is seeking to degrade the rind with chemical and enzyme treatments.
He's also evaluating different combination of temperatures, yeasts, antifoaming agents and pH levels to optimize the system.
Lane scientists also are examining annual ryegrass, sorghum and other crops that could be rotated with watermelons to furnish processing plants with a year-round supply of nutraceuticals or ethanol.