Quantification, localization and identification of selenium in seeds of canola and two mustard species compared to seed meals produced by hydraulic press

Authors: Banuelos, Gary; Walse, Spencer; YANG, S - University Of Saskatchewan; PICKERING, I - University Of Saskatchewan; FAKRA, S - Lawrence Berkeley National Laboratory; MARCUS, M - Lawrence Berkeley National Laboratory; FREEMAN, J - Fresno State University

Submitted to: Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2012
Publication Date: 6/29/2012
Citation: Banuelos, G.S., Walse, S.S., Yang, S.I., Pickering, I., Fakra, S., Marcus, M., Freeman, J. 2012. Quantification, localization and identification of selenium in seeds of canola and two mustard species compared to seed meals produced by hydraulic press. Analytical Chemistry. 84(14):6024-6030.

Interpretive Summary: Soils located on the western side of California's San Joaquin Valley are naturally laden with inorganic selenium, which can accumulate in the aquatic systems to levels that are toxic to a variety of organisms. Phytoremediation strategies have been adopted that utilize mustard and canola plants to manage the soluble selenium levels in the soil by plant uptake. Plants can then be harvested and their seeds are pressed to extract oil for biodiesel production. The resulting selenium-enriched seed meals are then used to supplement livestock feed with more bioavailable forms of selenium. In this study, we combined a variety of analytical techniques to measure total selenium, as well as other forms of selenium in the seed and in the seed meal after oil pressing. The results demonstrated that we must use more than one type of selenium analysis to accurately identify the biochemical changes that occur with the forms of selenium contained within the seed and within the processed seed meal. This new knowledge for analytically detecting selenium speciation changes is nutritionally important when using mustard and canola seed meals as supplemental sources of selenium for promoting healthy animal production.

Technical Abstract: Brassica plants accumulate selenium (Se), especially in seeds, when grown in soils laden with Se in the westside of the San Joaquin Valley. In this study, we attempt to accurately determine the forms of Se present in the Se-enriched products produced from plants grown for the phytomanagement of Se. We report on a chemical analysis strategy to identify Se forms in both Brassica seeds (canola, Indian mustard and white mustard) and in hydraulically-pressed seed meals (processed for biofuel), which are then used as a Se supplement in livestock animal feed rations. Complimentary analytical techniques were used to measure total Se concentrations, map the localization of Se, and to quantify different Se forms in seed and in seed meals. Seeds and hydraulically-pressed seed meals contained an average of 1.8 and 2.0 g Se mg Se/kg DW, respectively. Selenium was primarily located in cotyledons and roots of seed embryos. Micro-focused Se K-edge XANES and bulk-XANES showed that seeds contained 90% of Se as C-Se-C forms, modeled as selenomethionine (SeMet). Hydraulically pressing seeds for oil caused changes in the distribution of Se forms as follows: 40-55% C-Se-C (SeMet), 33-42% selenocystine, 5-12% selenocysteine and 11-14% trimethylselenium ion. Aqueos extracts of seed and seed meals were also analyzed by SAX-HPLC-ICPMS and found to contain the same forms of Se listed above, as well as MeSeCys, which is of dietary pharmacological interest for improving animal health. The reported analytical techniques clearly demonstrate the necessity of utilizing a multitude of analyses to accurately identify the Se changes that occur within the seed products after oil extraction. These reported analyses can be used to determine the true nutritional value of Se when the processed seed meal is used as a source of Se for animal production.