Culinary chemistry promotes the evolution of complex life

The Maillard reaction forms a brown crust on bread Credit: imageBROKER/Unai Huizi Alamy

A chemical reaction that gives flavor to cooked food could trap millions of tons of carbon at the seafloor each year. The process may even help create the conditions for the evolution of complex life.

When the temperature rises above about 140 ° C, a Maillard reaction occurs between sugars and amino acids. This chemical process produces a complex array of carbon-rich compounds that provide color and flavor to foods such as grilled meats, roasted vegetables, and toasted bread.

Minerals containing manganese can act as catalysts to allow the reaction to occur at temperatures as low as 25°C.

To explore whether this could happen at lower temperatures, Caroline Peacock and colleagues at the University of Leeds in the United Kingdom added iron or manganese minerals to a solution containing the sugar glucose and the amino acid glycine.

When the mixture was cultivated at 10°C, a temperature roughly equivalent to the seabed at the continental margin, the minerals accelerated the Maillard reaction by about 100 times compared to a mixture of sugars and amino acids without a catalyst.

Further analysis revealed that this process produced compounds found in marine sediment samples. Peacock says this suggests that the Maillard effect typically occurs on the ocean floor, where iron and manganese minerals are often found.

At the bottom of the sea, dead plants and animals provide a source of sugar and amino acids, which microbes ingest as an energy source. In this process, microbes convert carbon from dead organisms into carbon dioxide, which can re-enter the atmosphere.

If the Maillard reaction occurs on the ocean floor, Peacock said, it could lead to carbon in sugars and amino acids being stored in large, complex polymers, which are harder for microbes to ingest.

Over thousands or millions of years, these polymers will be buried deeper on the ocean floor as dead matter piled up on the seafloor. “If carbon can be allowed to pass through a 1-metre hazard zone at the top of the seafloor, carbon will normally be degraded by microbes and converted into carbon dioxide, which will isolate it from the atmosphere,” Peacock said. ”

Researchers estimate that iron and manganese minerals could lock in about 4 million tons of carbon per year. Without this process, Earth’s atmosphere could warm by a further 5°C over the past 400 million years.

Peacock said they also estimate that the Maillard reaction in ocean sediments may have increased atmospheric oxygen levels by 8 percent over the past 400 million years, as blocking carbon allows more oxygen to enter Earth’s atmosphere.

“This process has a profound impact on oxygen levels in the atmosphere,” she said, “because complex life forms require more oxygen and energy.” We think it is reasonable to assume that this process played a role in creating the conditions needed for complex life. ”

Peacock said the team also found that this reaction can occur in soils containing iron and manganese minerals, suggesting that increasing the mineral content in soil helps capture carbon from the atmosphere.

“This is a great study,” says Jan Amend of USC, “which highlights how iron and manganese chemistry, which has been overlooked in most climate and atmospheric studies, plays a huge role in atmospheric chemistry and Earth’s surface temperature.”

The researchers reported the findings in the August 2 issue of Nature. (Source: China Science News Guo Yueying)

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