Impact of Wheat Grain Selenium Content Variation

Cereal Chem. 88(2):195–200 Selenium (Se) is an essential micronutrient in animals. High levels of Se can accumulate in wheat grain, but it is not clear how high Se affects milling or baking. Low and high Se grain from the same hard red winter wheat cultivar was milled and used for breadbaking studies and Se analysis. Mill stream yields from the low and high Se wheat were comparable, as were flour yields. The amount of total grain Se retained in the flour mill streams was 71.2 and 66.4% for the low and high Se wheat, respectively. Proportionally, Se content in the bran, shorts, and the first reduction flour stream in high Se wheat was higher by 13–20% compared to the low Se wheat. Flour quality parameters including protein content, ash content, and farinograph traits were similar in low and high Se flours, although high Se flour mill streams exhibited lower farinograph stability. Breadbaking evaluations indicated that high Se had a deleterious effect on loaf volume. There was no evidence of significant Se loss after breadbaking with either low or high Se flour. Selenium (Se) was identified as an essential animal nutrient in the 1950s (Schwarz and Foltz 1957), and an abundance of research since then has elucidated its role in the prevention of animal diseases such as white muscle disease of ruminants (Combs 2001). A multitude of human health conditions also appear to be affected by selenium status of the individual; these conditions include cardiac, immune, and endocrine function and possibly behavioral and cognitive functions (Ryan-Harshman and Aldoori 2005; Li 2007; Rayman 2008). The Se status of human populations varies greatly, and it is estimated that Se deficiency afflicts as many as 1 billion people globally, particularly in certain regions of the world including parts of China (Combs 2001). In addition to its role as an essential nutrient, the relationship between improved Se status and reduced cancer risk in humans has been studied extensively (Ryan-Harshman and Aldoori 2005; Gromadzinska et al 2008). While results of these studies can often be contradictory, the efficacy of selenium appears to depend on selenium status of the individual, the chemical form of selenium, and the specific cancer. Nonetheless, there is some evidence that in subjects with low selenium status, more intake of Se may reduce cancer incidence (Duffield-Lillico et al 2002). Thus, increasing the Se intake in human populations may improve health by ensuring that minimum daily levels of the nutrient are provided to protect against the occurrence of Se deficiency-related diseases. The primary source of Se for humans is through the food chain, with a significant amount of Se derived from plant sources (Finley 2007). Indeed, in the United States, the largest single source of Se in diets is wheat products (Gerrior and Bente 2002). In contrast to animals, Se is not an essential nutrient for plants. However, Se is still absorbed by plants as an analog of the mineral macronutrient sulfur (Ellis and Salt 2003). Thus, plant Se content is largely determined by the amount of Se in the soil on which plants are grown, with other factors also playing a role (Gissel-Nielsen et al 1984). Thus, in regions of the world where soil Se is low, the crops grown on them are low in Se. Similarly, some regions harbor soils that are replete with Se owing to geological history, and crops grown on such highly seleniferous soils can accumulate inordinately high levels of Se (Finley 2007). In the United States, states in the northern Great Plains have regions with high soil Se levels (Kubota et al 1967). Wheat grain Se concentrations >60 μg/g have been reported from fields in South Dakota (Moxon et al 1943). To achieve the greatest effect, dietary Se supplementation efforts should target crops that are already a major component of human diets. Wheat is just such a crop; it is grown around the world and is a primary staple crop in human diets. Further, wheat exportation and importation is an established global trade activity. Thus, wheat is an ideal crop to employ as a source of dietary Se and has been proposed as a source for large-scale biofortification efforts (Lyons et al 2003). For wheat producers who grow wheat on highly seleniferous soils, an opportunity exists to market wheat with atypically high Se levels (“high Se wheat”) as a value-added trait. However, indepth analyses of the effect of high grain Se levels on wheat quality are not available. Such information is important because end use quality is an extremely important feature of wheat. This study sought to compare a range of quality attributes of a hard red winter wheat cultivar with typical (“low Se”) versus high Se levels, and to compare the relative retention of Se in products made with these wheats. MATERIALS AND METHODS Grain Source and Physical Characteristics Grain of the hard red winter wheat (Triticum aestivum L.) cultivar Nekota released by the University of Nebraska (Haley et al 1996) was used for this study. The grain was sourced from two locations in South Dakota. The low Se Nekota grain was obtained from the South Dakota Certified Seed Foundation and had been harvested from a field in Brookings, SD, located in the east central region of the state. The high Se Nekota grain was obtained from a ranch in central South Dakota, from a field known to produce high Se wheat due to intrinsic soil properties. Physical characteristics of grain including kernel test weight (lb/bu), size distribution, 1,000 kernel weight, hardness, ash content (14% mb), and protein content (12% mb) were measured according to AACC Approved Methods. Milling Procedures Forty pounds of cleaned grain sample was tempered to 16.0% mb, conditioned for ≈16 hr, and milled in a Bühler laboratory 1 USDA-ARS Plant Science Research Unit, 411 Borlaug Hall, University of Minnesota, 1991 Upper Buford Circle, St. Paul, MN 55108. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. 2 Corresponding author. E-mail: [email protected] 3 USDA-ARS Wheat Quality Laboratory, Harris Hall, North Dakota State University, Fargo, ND 58105. 4 USDA-ARS Grand Forks Human Nutrition Research Center, 2420 2nd Ave N., Grand Forks, ND 58203. 5 Current address: United States Department of Agriculture, Agricultural Research Service, 5601 Sunnyside Avenue, Beltsville, MD 20705-5138. doi:10.1094/CCHEM-05-10-0076 This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. AACC International, Inc., 2011.