In 2023, researchers oxidized orange-peel waste for 1 hour and recovered 55% of its sugars; engineered E. coli produced up to 393 mg of PHB

Each glass of orange juice leaves behind a huge pile of peels that either end up in the landfill or get burned. But what if this waste could be turned into plastic? Researchers from Cornell University, in a study titled 'One-Step Oxidation of Orange Peel Waste to Carbon Feedstock for Bacterial Production of Polyhydroxybutyrate,’ found a new way for achieving just this. They treated the orange peels with a chemical for an hour, extracted more than half of their sugar content, and used the residue to feed bacteria that produced PHB plastic.

The problem hiding in your fruit bowl

Oranges are among the most heavily processed fruits in the world. According to FAO data cited in peer-reviewed literature, global orange production reached roughly 75 million metric tons in a recent reporting year, and of this total, 50%-60% becomes waste after juice extraction, as documented in the peer-reviewed analysis, 'Utilization of orange peel waste for sustainable amino acid production by Corynebacterium glutamicum,' published in Frontiers in Bioengineering and Biotechnology. Fruit peels spoil quickly, which makes them difficult to store and process. For decades, this fruit waste has been discarded despite its nutritional value.


The main barrier to turning orange peels into something useful has been a compound called limonene. It's the oily substance that gives citrus its sharp, zesty smell. It smells nice, but limonene is toxic to many bacteria. The Cornell study found that even a residual limonene concentration as low as 1% can reduce the growth rate of some bacteria strains by 60%. So, before anyone can access the sugar locked inside orange peels, they need to get rid of the limonene without destroying the sugar in the process.

Turning peel into plastic-making sugar

In their experiment, the research team mixed the chemical potassium superoxide with ground-up orange peel. Potassium superoxide breaks down limonene and releases sugar stored within orange peel fibers. Everything happens in a single vessel with no additional steps. The team tested different strengths and timings, and found that a moderate dose of the chemical, applied for just one hour, was the most effective. The researchers reported that the process recovered 55% of all the sugar present in the orange peel, while clearing out the limonene that would otherwise have blocked bacterial growth. That one-hour window matters because several competing techniques for converting waste into fuel or plastic require far longer processing times, along with more toxic chemicals or heat, making this approach potentially cheaper to run and easier to scale.

Plastic created by sugar-eating bacteria

Once the sugar solution was ready, the researchers fed it to a lab-made strain of Escherichia coli, also known as E. coli. This strain had been designed to convert sugar into a natural plastic called polyhydroxybutyrate, or PHB. PHB naturally biodegrades in soil and water, unlike plastic made from crude oil. The bacteria consumed the orange peel sugar. The study found that at a 3% concentration of peel liquor, the concentration level the researchers identified as optimal for bacterial health, not a hard ceiling on how much peel liquor a scaled-up process could use, cells were 90% to 100% healthy and viable, a good indication that the sugar-rich liquid was not toxic to them even after treatment. Over 24 to 96 hours of fermentation, the bacteria produced 136 to 393 milligrams of PHB, which represented 8 to 13 percent of the bacteria's total dry weight. The plastic they created also had a very high molecular weight, a property that can improve durability and make bioplastics more suitable for real-world products.

Why this could matter for the plastic crisis

The world is drowning in plastic. Global plastic waste generation reached 353 million tonnes in 2019, and the OECD's Global Plastics Outlook projects it could nearly triple by 2060 if no major policy changes are made. Traditional plastics can take hundreds of years to decompose and are made from fossil fuels. Bioplastics like PHB offer an alternative route, but can be expensive to produce, partly because the sugar to feed the bacteria often comes from food crops like corn.

Using orange peel waste instead changes that equation. They are cheap, abundant, and would have ended up being disposed of. If the process is made commercially viable, the juice companies could turn their leftover peels into raw material for biodegradable packaging instead of paying for disposal. That alone won’t solve the plastic problem, but it could help point the way toward a future in which yesterday’s fruit waste becomes tomorrow’s plastic bottle.