Accumulation and speciation of selenium in biofortified vegetables grown under high boron and saline field conditions

Authors: Banuelos, Gary; FREEMAN, JOHN - National Aeronautics And Space Administration (NASA); Arroyo, Irvin

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2019
Publication Date: 12/20/2019
Citation: Banuelos, G.S., Freeman, J., Arroyo, I.S. 2019. Accumulation and speciation of selenium in biofortified vegetables grown under high boron and saline field conditions. Food Chemistry. 5. https://doi.org/10.1016/j.fochx.2019.100073.
DOI: https://doi.org/10.1016/j.fochx.2019.100073

Interpretive Summary: Plant-based foods are the major dietary sources of selenium (Se) in many countries around the world, followed by meats and seafood. Human Se intake and Se status in a population depends firstly on Se concentration in soils, and the Se concentrations in the harvested edible plant product grown in these soils. In the westside of California, an agronomic strategy called biofortification produces Se-enriched food products by growing crops in unproductive soils with naturally high levels of Se. In this biofortification study, different Brassica vegetables and Swiss chard were field-grown in high boron (B) and saline soils containing natural and variably high levels of Se. All plant species appeared to be salt- and B-tolerant and were harvested 86 days after transplanting. After elemental analyses in plant tissues, Se and all macro-and micronutrient concentrations significantly increased in all plant species. Additionally, Se speciation analyses showed that organic Se species were the predominant forms of Se measured in most vegetables. In food products, organic forms of Se are generally more bioaccessible than inorganic forms of Se, and upon consumption, organic Se can result in a higher intake of Se. Our results demonstrate that we can naturally produce Se and other mineral-nutrient-biofortified vegetables from unproductive saline and B California soils laden with Se. Identifying salt- and B-tolerant vegetables that can accumulate significant amounts of Se and other nutrients from westside soils of Central California is an alternative “biofortification crop strategy” that may have both economic benefit for growers and nutritional benefit for inhabitants susceptible to low Se intake.

Technical Abstract: In a Se-deficient region, one of the most promising approaches to mitigate a low transfer of Se from soil into the food chain involves the use of a strategy called Se biofortification. Selenium biofortification, as an agronomic-based strategy, can be utilized to produce Se-enriched food products that may help reduce dietary deficiencies of Se occurring throughout susceptible regions of the world. In the westside of California, naturally high levels of Se in saline/boron soils result in the poor production of typical agronomic crops. In this biofortification field study, we evaluated the salt and B tolerance of Brassica species broccoli (Brassica oleracea var. italic), red cabbage (Brassica oleracea var. capitata f. rubra), green cabbage (Brassica oleracea L. var capitata), savoy cabbage (Brassica oleracea var. sabauda L.) and Swiss chard (Beta vulgaris L. var cicla) and measured their abilities to accumulate Se and other macro- and micronutrients under these poor growing conditions. After 86 days of growth, the apparent salt- and B-tolerant vegetables were harvested and processed for chemical analyses. We initially analyzed all plant tissues for total Se and all macro-micronutrients by inductive-coupled plasm (ICP)-MS. Additionally, we determined the chemical speciation of the soluble Se forms in aqueous proteolytic and non-proteolytic tissue extracts by an Agilent 1200 HPLC equipped with a Hamilton PRP-X100 strong anion exchange column coupled to the Agilent 7500 CX ICP-MS (SAX-HPLC-ICP-MS). All macro-and micronutrient concentrations significantly increased, and the uptake of Se readily occurred in all vegetables as follows: broccoli 10.0 mg Se kg-1 DM, green cabbage 13.1 mg Se kg-1 DM, red cabbage 17.2 mg Se kg-1 DM, savoy cabbage 11.0 mg Se kg-1 DM, and Swiss chard 4.8 mg Se kg-1 DM. The chemical speciation of organic Se compounds in the vegetables were found to be diverse and occurring most frequently as organic Se forms C-Se or C-Se-C ranging between 46-65% organic Se, respectively, while the inorganic form present was primarily the unreduced selenate (SeO4) ranging from 35-54%. The apparent salt and B tolerance exhibited by these tested species and their abilities to accumulate Se and all macro- and micronutrients, clearly shows that these vegetables could be considered as alternative crops to grow for natural biofortification in otherwise unproductive soils of the westside of Central California. Consumption of Se and nutrient-enriched vegetables may be a nutritionally sound strategy for increasing Se intake in Se-deficient areas after careful analyses for Se and the different selenoamino acids.