Production and processing of selenium rich wheat in South Dakota.

摘要

Selenium (Se) is an essential micronutrient for all animals, including human beings and wheat is the major dietary source of this element. An increasing public interest in the numerous health benefits of Se has promoted the production of Se-rich wheat based products. There is a paucity of information on Se content in South Dakota (SD) wheat, particularly in grain that is cultivated in soils that are naturally high in Se. An officially accepted fluorometric method for Se determination was applied for each sample, which was duplicated for accuracy and for reliable results.;A 3-year study on SD wheat investigated the 2 economic classes of wheat, Hard Red Winter (HRW) and Hard Red Spring (HRS), using processing techniques for obtaining Serich fractions. The HRW samples (n=344) where collected from 4 different growing locations and the HRS samples (n=160) were obtained from 2 different locations.;A total of 504 samples analyzed for Se concentration over 3 growing years ranged from 0.06 mug g-1 to 3.12 mug g-1 in all-wheat (HRS and HRW). The mean grain Se content of HRS was significantly higher than that of HRW. Growing location was a significant factor influencing the variability of the Se content within either class of wheat (HRS and HRW). Selby (HRS) and Kennebec (HRW) were found to be the growing locations with highest Se content in wheat, achieving Se concentration in excess of 1mug/g.;The distribution of Se in wheat fractions using roller milling (Quadrumat mill), pearling, and scarification was investigated. These processing protocols were based on the 3 composite samples namely high (> 0.85 mug g-1 ), medium (0.55 mug g-1 to 0.85 mug g-1 ) and low Se wheat ( 0.54 mug g-1). Sample Se distribution varied from year to year. Mean, median and outer box values for Se in the wheat were determined using box-plots.;Roller milling, scarification and pearling were explored as fractionation techniques to separate grain components. Milling of wheat kernels yielded bran and endosperm. Scarification resulted in mill fractions. However these fractions were difficult to recover. Pearling, in comparison to scarification, was found to be a better processing technique for fractionation of outer portions of wheat kernel for the purpose of mass distribution of Se and other minerals. Pearling was deemed to be effective because of minimal losses ( 4%) in case of operation. In addition mass fractions were predictable and repeatable in pearling. Flour extraction rates using convention roller milling (Quadrumat mill), pearling for 60 seconds, scarification for 60 seconds and pearling for 5 minutes ranged from 64% to 72%, from 82% to 86%, from 58% to 60% and from 66% to 73% respectively. Pearling for 5 minutes was found to comparable to the results obtained from conventional physical separation with an average flour extraction rate of 69%. It was found that Se was uniformly distributed (had similar concentration) within the outer portions of the kernel after pearling for 5 minutes. The percentage distribution of Se showed that a significant proportion of the grain Se (36%) is present in the outer portions (bran and aleurone layers), which constitutes 27% by weight of the whole grain. Statistical analysis showed that Se concentration in each of the four outer fractions (1 to 4) was not significantly different from each other. Of the pearling fractions, the concentration of protein (%) was highest in 2nd fraction and 3rd fraction, indicating the presence of aleurone layer. These high Se fractions can have a role in supplementation and enrichment of wheat products.;The distribution of Se within different pearling fractions of wheat was compared to that of other mineral elements (Ca, Cu, S, Mn, Mg, Mo, Zn, Fe, and K). The concentration gradient of Se was found to be different from that of most of the other minerals (except S, Ca, and Fe). Relative to Se, the concentration gradient was significantly steep in Cu, Mn, Mg, Mo, Zn and K, whose concentration in the bran was found to be significantly higher than in the flour. The flour retained around 60% of the total Se of the whole grain in contrast to distribution of other minerals in the grain.