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Brazil nuts' selenium storing secrets revealed?
19 October 2006
Brazil nuts are a rich source of selenium, an essential trace element, and now scientists have identified 15 selenium-containing peptides in the tasty treats.
The discovery should help them to understand why Brazil nuts are so good at accumulating selenium.
Selenium is believed to offer protection against heart disease and to help prevent cancer particularly of the prostrate. It is also a powerful antioxidant - meaning that it can protect cells from free radical damage. Brazil nuts are one of the best sources of selenium containing about 2500 times as much as any other nut.
The selenium peptides were by identified by Ryszard Lobinski and colleagues from the University of Pau and the Adour, France, who have detected, fragmented and sequenced 15 new selenium peptides from Brazil nuts.
Brazil nuts are one of the best sources of selenium
Lobinski started by breaking down the Brazil nut proteins using the digestive enzyme trypsin. He then used two stages of size exclusion chromatography coupled with ICP (inductively coupled plasma) mass spectrometry (MS) to purify and concentrate the selenium-containing compounds.
In the next step, the researchers used two mass spectrometry techniques in parallel. The first - based on ICP - allowed the researchers to work out how long it took the peptide to pass through a chromatography column. Using this information, the team then used a second technique - electrospray ionisation - to pick out characteristic selenium isotope patterns of the peptides. They could then fragment and sequence these peptides to identify them.
Sam Houk from the Iowa State University, Ames, US, said, 'this is an excellent example of the value of element-specific information from ICP-MS combined with molecular information from ESI-MS in studies of proteins or peptides with heteroatoms. Neither technique alone could identify these seleno proteins.'
M Dernovics, P Giusti and R Lobinski, J. Anal. At. Spectrom., 2006