Hydrogen peroxide from tea and coffee residue: New pathway to sustainability

H₂O₂ has a lot of industrial value; this chemical plays a critical role in the oxidation of several compounds. The oxidation process is typically catalyzed by an enzyme called P450 peroxygenase, but it can't occur unless H₂O₂ is present. These oxidation reactions are used to produce many chemicals of note. Now, H₂O₂ is currently produced through an unsustainable method called the anthraquinone process, which is not only energy-intensive but also produces a lot of waste, highlighting the need for a greener, environmentally friendly alternative. While there are other methods which use enzymes or light to produce H₂O_2, these are expensive because they require catalysts and additional reagents.

Keeping these issues in mind, a group of scientists from Japan -- including Associate Professor Toshiki Furuya and Mr. Hideaki Kawana from Tokyo University of Science, and Dr. Yuki Honda from Nara Women's University, Japan -- has found an alternative way to produce H₂O₂. Their product comes from an unlikely source -- the leftovers of brewed tea and coffee, called spent coffee grounds (SCG) or tea leaf residue (TLR)!

"Given their polyphenol content, we predicted that SCG and TLR could be used to produce hydrogen peroxide," says Dr. Furuya. Proving their prediction to be true, their study -- published in ACS Omega on June 1, 2022 -- details their successful production of H₂O₂ using these underutilized biomass resources.

The team's production method involved adding coffee grounds and tea leaves to a sodium phosphate buffer, then incubating this solution while shaking it. In the presence of the buffer, SCG and TLR interacted with molecular oxygen to produce H₂O₂.

The team also explored the scope of using this H₂O₂ to synthesize other chemicals of industrial importance. The newly-synthesized H₂O₂ aided in the production of Russig's blue. Moreover, in the presence of peroxygenase (an enzyme that catalyzes an oxidation reaction using H₂O₂),TLR- and SCG-derived H₂O₂ was allowed to react with a molecule called styrene to produce styrene oxide -- which has several applications in medicine -- and another useful compound, phenylacetaldehyde.

These results prove that the team's new approach of using SCG and TLR to produce H₂O₂ proved to be simple, cost-effective, and environmentally friendly, compared to the traditional anthraquinone process. Hailing these promising results, Dr. Furuya says, "Our method can be used to produce hydrogen peroxide from materials that would otherwise have been discarded. This could further result in new ways to synthesize industrial chemicals like styrene oxide, opening up new applications for these unused biomass resources."

These findings thus open up a new way towards the sustainable production of H₂O₂, from the most unexpected sources: tea and coffee waste!