Reject watermelons promise new biofuel source

Thousands of tonnes of watermelons left to rot in American fields every year could provide a valuable source of biofuels, scientists believe.

Around one in five cultivated watermelons, equivalent to 360,000 tonnes of fruit, is rejected for sale because it is misshapen or has surface blemishes. At present the unwanted produce is ploughed back into the ground.

Researchers at the USDA-Agricultural Research Service’s South Central Agricultural Research Laboratory in Lane, Oklahoma tried fermenting the juice from reject melons in a laboratory, combining it with sugar and molasses bought from a local supermarket.

Writing in BioMed Central’s open access journal Biotechnology for Biofuels, they report that it is possible to produce around 0.4g of ethanol from each 1g of sugar in the feedstock. On an industrial scale, they say, that would convert to approximately 220 litres of ethanol from the waste fruit left in each hectare of farmland.

“We’ve shown that the juice of these melons is a source of readily fermentable sugars, representing a heretofore untapped feedstock for ethanol biofuel production,” said project leader Wayne Fish.

As well as using the juice for ethanol production either directly or as a diluent for other biofuel crops, Fish added, it can be a source of lycopene and L-citrulline, two ‘nutraeuticals’ for which enough demand currently exists to make extraction economically worthwhile. After these compounds have been removed from the ‘cull’ juice, it can still be fermented into ethanol.

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