Brazil nuts have been promoted as a supplement to a healthy diet since the late 1970’s. This is due to their unusually high selenium content, an essential trace element known to be a powerful antioxidant and to reduce the likelihood of conditions such as heart disease and prostate cancer.

Recent research by Ryszard Lobinski and colleagues at the University of Pau and the Adour (France) has shown that the selenium compounds contained in Brazil nuts are seleno-peptides, and have developed a new method for their extraction, purification and characterisation. This has led to the discovery of 15 new seleno-peptides. Their research should help us to understand why Brazil nuts are so good at accumulating selenium.

The first step is to purify the sample, as the seleno-peptides are outnumbered by sulphur analogues. This was done using size exclusion chromatography with proteins and tryptic peptides, and then enriching the selenium containing fractions. After this a combination of two techniques was used. ICP-MS to measure the retention times of the peptides, then ESI mass spectrometry to identify characteristic selenium isotope patterns, leading to the isolation of selenium containing fractions. This resulted in the identification of 15 different seleno-peptides.

These results gives clues as to why Brazil nuts are an excellent source of selenium containing about 2500 times as much as any other nut.

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Reference: M Dernovics, P Giusti and R Lobinski, J. Anal. At. Spectrom., 2006 [DOI: 10.1039/b608041c]