Wheat is able to accumulate Se at higher levels than previously recognised. Interestingly, even when the plant is exposed to exceedingly high concentrations of inorganic Se, the Se taken up by the roots is extensively biotransformed into a variety of organoselenium compounds, with Selenomethionine being the main compound.
Background:Selenium (Se) is an essential micronutrient for humans and animals, involved as selenocysteine (SeCys) in functioning at the catalytic center of several selenoproteins. These selenoproteins play a major role in the protection of body tissues against oxidative stress, immune function, reproduction, and modulation of growth and development. Selenium is also considered to be an antagonist against toxic metallic species, such as mercury, lead and cadmium.
Selenium deficiency, caused by extremely low dietary intakes, has functional consequences that result in severe disease conditions in domestic livestock and have been observed in humans as well. In recent years, interest in Se as related to human health has been stimulated by the possible adverse health effects of marginal Se undernutrition as well as the potential of Se supraphysiological intakes in cancer chemoprevention. Such chemoprevention has been studied and is still under investigation. Increasing Se intake is possible through use of enriched food, fortified food, or Se supplements (e.g., Se-enriched yeast).
Wheat is one of the most important Se sources for humans with Se concentrations ranging from < 0.02 µg/g in Se-deficient areas and upto 30 µg/g in seleniferous regions. Seleniferous areas have been identified in China and India.
Because of the narrow range existing between Se deficiency and toxicity (only a factor of about 10) , and since plants can accumulate huge amounts of Se if present in a bioaccesible form in soil, poisoning of livestock and other animals grazing high-Se lands is well-known. For a meaningful assessment of the risks for the local population, the transfer of soil Se to plant Se should be known but also the speciation of selenium in the plant that defines its bioavailability.
The new study:An international group of researchers from Italy and India have investigated the situation in the seleniferous
Nawanshahr-Hoshiarpur Region (
Punjab, India). The identity and content of the selenocompounds in locally harvested wheat grain samples was investigated by
HPLC-ICP-DRC-MS. Reversed-phase, cation exchange, and anion exchange HPLC were used to separate the selenium species after ultrasound-assisted enzymatic extraction.
Francesco Cubbada, the corresponding author of the group, summarized the main findings for us: "Even when the wheat plant is exposed to exceedingly high concentrations of Se, the inorganic Se taken up by the roots is extensively biotransformed into a variety of organoselenium compounds, which are then found in the kernel and account for 97% of the extracted Se on average. In the samples with very high total Se concentrations in grains, SeMet remains the major Se-compound but it shows a relative reduction whereas the other organoselenium compounds increase."
This is good and bad news. Regular consumption of locally produced wheatbased food items may lead the population of the study area to an excessive intake of selenium. On the other hand, the large predominance of selenomethionine shows that local wheat can be a promising raw material for naturally enriched products to be used to supplement human and animal diets in low selenium areas.
The original study
Francesco Cubadda, Federica Aureli, Silvia Ciardullo, Marilena D’Amato, Andrea Raggi, Raghunath Acharya, Ramana A.V. Reddy, Nagaraja Tejo Prakash,
Changes in Selenium Speciation Associated with Increasing Tissue Concentrations of Selenium in Wheat Grain, J. Agric. Food Chem., 58/4 (2010) 2295–2301.
DOI: 10.1021/jf903004a Related studies (newest first)
Heidi Goenaga Infante, Mike Sargent,
Key comparison CCQM-K60: Total selenium and selenomethionine in selenised wheat flour, Metrologia, 47 (2010) 08012.
DOI: 10.1088/0026-1394/47/1A/08012 Francesco Cubadda, Federica Aureli, Andrea Raggi, Marina Carcea,
Effect of milling, pasta making and cooking on minerals in durum wheat, J. Cereal Sci., 49/1 (2009) 92-97.
DOI: 10.1016/j.jcs.2008.07.008 N. Sharma, R. Prakash, A. Srivastava, U.S. Sadana, R. Acharya, N.T. Prakash, A.V. Reddy,
Profile of selenium in soil and crops in seleniferous area of Punjab, India by neutron activation analysis, J. Radioanal. Nucl. Chem., 281 (2009) 59– 62.
DOI: 10.1007/s10967-009-0082- Hua-Fen Li, Steve P. McGrath, Fang-Jie Zhao,
Selenium uptake, translocation and speciation in wheat supplied with selenate or selenite, New Phytol., 178/1 (2008) 92-102.
DOI: 10.1111/j.1469-8137.2007.02343.x J.K. Kirby, G.H. Lyons, M.P. Karkkainen,
Selenium speciation and bioavailability in biofortified products using species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry, J. Agric. Food Chem., 56 (2008) 1772– 1779.
DOI: 10.1021/jf073030v Malcolm J. Hawkesford, Fang-Jie Zhao,
Strategies for increasing the selenium content of wheat, J, Cereal Sci., 46/3 (2007) 282-292.
DOI:10.1016/j.jcs.2007.02.006 Graham H. Lyons, Yusuf Genc, James C. R. Stangoulis, Lyndon T. Palmer,
Robin D. Graham,
Selenium distribution
in wheat grain, and the effect of postharvest processing on wheat
selenium content, Biol. Trace Ele. Res., 103/2 (2005) 155-168.
DOI:
10.1385/BTER:103:2:155 M. Stadlober, M. Sager, K.J. Irgolic,
Effects
of selenate supplemented fertilisation on the selenium level of cereals
- identification and quantification of selenium compounds by
HPLC-ICP-MS,
Food Chem.,
73 (2001)
357–
366. DOI: 10.1016/S0308-8146(01)00115-7
Related EVISA Resources Link Database: Selenium and Human Health Link Database: Selenium and Animal Health Link Database: Selenium in the Environment
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