The Maillard reaction – the chemical process that gives browned food its flavour – may play a role in storing sedimentary organic carbon on the seafloor. The researchers behind the discovery say it could lead to a better understanding of the underlying chemistry involved in climate processes.

It has previously been suggested that the Maillard reaction might occur in marine sediments, transforming sugars and amino acids into complex structures that can’t be broken down by microbes. However, it was thought that at the temperature of the seabed – around 10°C – the reaction would be too slow to play a significant role in the preservation of organic carbon.

More recent studies have suggested that reactive forms of iron and manganese may complex with the organic molecules in sea sediments, but the potential of these metals to catalyse the Maillard reaction had not been fully determined.

To find out more, an international team of researchers incubated common organic molecules with different forms of iron and manganese to determine their catalytic effect under conditions that replicate those at the seafloor. The team observed that the reactive forms of iron and manganese catalysed the Maillard reaction by up to two orders of magnitude, compared to the catalyst-free control. The reaction products were consistent with the chemical signature of sediment samples taken from various marine locations.

‘The Maillard reaction takes two small molecules – a reducing sugar and an amino acid – and polymerises them into larger molecules,’ explains project leader Oliver Moore, who researches aqueous geochemistry at the University of Leeds, UK. ‘This is known to occur quicker at higher temperatures, such as when cooking a steak. However, we show it is catalysed at low temperatures … by aqueous and solid forms of iron and manganese commonly found at the bottom of the ocean.’

The researchers estimate that the Maillard reaction could account for the burial of around four million tonnes of carbon globally each year, which might otherwise be returned to the atmosphere as carbon dioxide following microbial degradation.

‘We are now investigating where else on Earth this reaction might occur, such as within the plumes of underwater volcanoes … where there are often high temperatures and high iron and manganese concentrations,’ Moore adds.

David Burdige, an expert in marine geochemistry from Old Dominion University in Virginia, US, who wasn’t involved in the project urges caution when using the finding to extrapolate how much carbon might be locked away by the Maillard reaction.

‘But I think I think this is a good first start – it points out a unique twist on processes that could be important that haven’t been fully explored,’ he adds. ‘[Moore’s team is] postulating that this is a potentially important mechanism that has been underappreciated, and I think they’re absolutely right.’