The Maillard Reaction Helped Life On Earth To Thrive

The Maillard reaction – most famously known for its role in browning meat and caramelizing sugars during cooking – may have played an important role in protecting early life, new research has found. This chemical process also occurs in the oceans, with the new study confirming that the reaction has helped to trap organic carbon in the sea floor and reduce carbon dioxide levels in the atmosphere. The research is published in the journal Nature.

Organic carbon and the Maillard reaction

The Maillard reaction, named after the French chemist Louis Camille Maillard who discovered it, is a very complex process. In cooking, it describes the formation of melanoidins – the compounds which give hot food its browned hue – through reacting reducing sugars and proteins using heat. But the reaction also occurs in nature, where it converts small molecules of organic carbon into larger polymers.

Organic carbon in the oceans comes from the death of microscopic living organisms predominately. When these organisms die and sink to the bottom of the oceans, they decay. This decaying process uses up oxygen and releases carbon dioxide into the ocean, which will bubble up to the surface and enter the atmosphere.

But with the Maillard reaction, some of this organic carbon can be captured or preserved through its conversion into larger molecules. By virtue of being larger, these molecules are more difficult to break down and so the carbon effectively becomes trapped in the marine sediment. In turn, this limits the amount of carbon dioxide that is released into the world.

While the existence of this reaction in sediment has been known for decades, it was believed that the process was very slow, and would have a negligible effect on the planet. However, researchers at the University of Leeds now believe that this process was fundamental to early life, where it helped to maintain the conditions needed for life to emerge and thrive on Earth.

Sea floor traps four million tonnes of carbon per year

In the new study, incubation experiments showed that iron and manganese ions – which are commonly found in seawater – can abiotically catalyze the Maillard reaction by up to two orders of magnitude at seabed temperatures. This speeds up the reaction process to a point where the researchers estimate that around 4 million tonnes of organic carbon could be locked into the seabed each year.

Dr. Oliver Moore, first author of the study and a research fellow in biogeochemistry at the School of Earth and Environment at Leeds, said: “It had been suggested back in the 1970s that the Maillard reaction might occur in marine sediments, but the process was thought to be too slow to impact the conditions that exist on Earth.”

“Our experiments have shown that in the presence of key elements, namely iron and manganese which are found in seawater, the rate of reaction is increased by tens of times. Over Earth’s long history, this may have helped create the conditions necessary for complex life to inhabit the Earth.” 

To confirm their hypothesis, the researchers also created a set of laboratory samples that had undergone the Maillard reaction and compared these to various near-shore sediment samples taken from around the world. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiment, conducted at the UK’s national synchrotron science facility – Diamond Light Source –  confirmed that both sets of samples shared similar chemical fingerprints.

Dr. Burkhard Kaulich, principal beamline scientist of the scanning X-ray microscopy beamline (I08-SXM) on which the NEXAFS experiments were performed, said: “Our advanced I08-SXM instrumentation with its high stability, energy and optical resolution was developed and optimized to help probe carbon chemistry and reactions which take place in environmental systems.”

“We are very proud to have been able to contribute to a better understanding of the fundamental chemical processes involved in the creation of complex life forms and climate on Earth.” 

A new avenue for understanding climate change

The study authors believe that over geological timescales, the presence of variable iron and manganese ions in the oceans could have exerted a substantial but so far unexplored impact on organic carbon preservation, and thus environmental carbon dioxide levels.

“It’s immensely exciting to discover that reactive minerals such as those made from iron and manganese within the ocean have been instrumental in creating the stable conditions necessary for life to have evolved on Earth,” said Professor Caroline Peacock, lead study author and professor of biogeochemistry at the University of Leeds.

Further exploration of this effect and how it has interacted with the Earth’s other geochemical processes over time could be used to harness new approaches to tackling climate change, the researchers said.

“Understanding the complex processes affecting the fate of organic carbon that is deposited on the seafloor is crucial to pinpointing how Earth’s climate changes in response to both natural processes and human activity, and helping humanity better manage climate change, since the application and long-term success of carbon capture technologies relies on carbon being locked away in stable forms rather than being transformed into carbon dioxide,” explained study co-author Dr. James Bradley, an environmental scientist at the Queen Mary University of London.

Reference: Moore OW, Curti L, Woulds C et al. Long-term organic carbon preservation enhanced by iron and manganese. Nature. 2023. doi: 10.1038/s41586-023-06325-9

This article is a rework of a press release issued by the University of Leeds. Material has been edited for length and content.