(Inside Science) -- Many may see the peel of an orange as an obstacle -- something they must defeat and discard in order to enjoy the sweet pulp inside. However, a new line of thought values the outside of the orange just as much as the inside.
Over 31 million tons of citrus fruits are produced globally each year, and Brazil and the United States alone produce about 38 percent of the world's oranges. The peels that are wasted after juicing, which account for 50 percent of the orange, are usually eliminated by burning, which produces carbon dioxide and other greenhouse gases, or dumping into landfills, where the oil from rotting peels percolates into the soil, harming plant life. In some cases, juicing plants both dry and detoxify their peels so they can be used in cattle feed, but even this process can be time-consuming and costly.
Chemists James Clark and Lucie Pfaltzgraff from the University of York in the U.K. proposed a solution to this unsustainable cycle at the recent Green Chemistry & Engineering Conference in Washington, D.C. The researchers have developed a one-step method that uses high-intensity microwaves at low temperatures to extract chemicals in orange peels for many uses.
These valuable chemicals include limonene, which can be used as a fragrance, in household cleaners and as a solvent holds promise to replace petroleum-derived products; pectin, often used in cosmetics, pharmaceuticals and in foods like jellies; and cellulose, which is used as a thickening agent or can be converted into a solid biofuel.
The project, known as OPEC (the Orange Peel Exploitation Company), began as a collaboration last year between the University of York, University of Sao Paulo, Brazil, and the University of Cordoba, Spain. Clark first presented the idea at the British Festival of Science last September, where he discovered that there was a good deal of interest in the initiative.
"Some companies have come along expressing interest in products, or equipment, or in the possibility even of building a bio-refinery where you could actually process the peel in one location to make products," Clark said.
Since then, the team has been working with small-scale juicers in Brazil, southern Europe, Africa and London to utilize these untapped feedstocks. Their goal is to install a microwave processor close to an existing juicing facility, creating a way to profit from the chemicals and fuel created from the waste. This would benefit small juicers and other facilities that have to pay for their peels to be taken away.
The emergence of these bio-based industries is an essential step in maintaining a sustainable economy and society in the future, according to Paul Anastas, founder of the Green Chemistry & Engineering Conference and Yale’s Center for Green Chemistry and Green Engineering in New Haven, Conn.
"The efforts to combine the best of science and innovation with the best of business and commercialization are tremendously important, and I applaud Professor Clark and all involved with this effort, as well as the many other efforts going on in this era," Anastas said.
Microwave processing orange peels has the potential to be beneficial to other juicers, according to Paul Winniczuk, quality assurance manager at juice producer Sun Orchard, in Haines City, Florida. Sun Orchard has a policy to produce "zero-citrus-waste," in which they pay for their peel to be picked up and sent out to multiple farms as cattle feed.
"I guess it all depends on the cost of the whole system," Winniczuk said. "If it was something that was cheaper than what we currently do, then it could be a viable alternative."
Clark and Pfaltzgraff are also experimenting with other citrus and food waste, including lemons, rice in Vietnam, sugar in Brazil, and various cereal straw and tea farming waste in the U.K.. A large-scale processing facility located in York will be fully operational this month, after which they’ll be running trials with orange peels and eventually other bio-waste like fruit and vegetable peels and cereal straws.
"There are enormous quantities of food supply chain waste in many parts of the world, which at the moment do very little. In some cases they’re actually an environmental problem," Clark said.
The big juicers in Brazil that Clark has approached have yet to jump on board with microwaving their peels. He and his team hope that success with smaller operations will persuade the larger juicers to adjust their current systems.
Allison Jarrell is a contributing writer to Inside Science News Service.