Niels De Brier

Distribution of Minerals in Wheat Grains (Triticum aestivum L.) and in Roller Milling Fractions Affected by Pearling.

The distribution of minerals in (pearled) wheat grains was measured by synchrotron X-ray fluorescence, and the impact of pearling (0, 3, 6, 9, and 12% by weight) on the mineral composition of flour, shorts, and bran was identified by ICP-MS. The xylem mobile elements (Mn, Si, Ca, and Sr) dominated in the outermost bran layers, while the phloem mobile elements (K, Mg, P, Fe, Zn, and Cu) were more concentrated in the aleurone. Pearling lowered the concentrations of xylem mobile elements and increased the concentrations of most phloem mobile elements in the pearled grains. Molybdenum, Cd, and especially Se were more evenly distributed, and pearling affected their concentrations in milling products less. Pearling (3%) increased the concentration of several nutrients (P, Zn, Cu) in the flour because the bran fractions reaching the flour are enriched in aleurone. The correlations of concentrations of Mg, Fe, Zn, and Cu with that of P suggested their association with phytate.

Element distribution and iron speciation in mature wheat grains (Triticum aestivum L.) using synchrotron X‐ray fluorescence microscopy mapping and X‐ray absorption near‐edge structure (XANES) imaging

Several studies have suggested that the majority of iron (Fe) and zinc (Zn) in wheat grains are associated with phytate, but a nuanced approach to unravel important tissue-level variation in element speciation within the grain is lacking. Here, we present spatially resolved Fe-speciation data obtained directly from different grain tissues using the newly developed synchrotron-based technique of X-ray absorption near-edge spectroscopy imaging, coupling this with high-definition μ-X-ray fluorescence microscopy to map the co-localization of essential elements. In the aleurone, phosphorus (P) is co-localized with Fe and Zn, and X-ray absorption near-edge structure imaging confirmed that Fe is chelated by phytate in this tissue layer. In the crease tissues, Zn is also positively related to P distribution, albeit less so than in the aleurone. Speciation analysis suggests that Fe is bound to nicotianamine rather than phytate in the nucellar projection, and that more complex Fe structures may also be present. In the embryo, high Zn concentrations are present in the root and shoot primordium, co-occurring with sulfur and presumably bound to thiol groups. Overall, Fe is mainly concentrated in the scutellum and co-localized with P. This high resolution imaging and speciation analysis reveals the complexity of the physiological processes responsible for element accumulation and bioaccessibility.

Incubation of Isolated Wheat Starch with Proteolytic or Lipolytic Enzymes and Different Extraction Media Reveals a Tight Interaction Between Puroindolines and Lipids at Its Granule Surface

ABSTRACT Differences in hardness of wheat cultivars have been related to differences in interactions between the starch granule surface and the gluten protein matrix that are mediated by the proteins puroindoline (PIN) A and B. We examined whether or not PINs and (polar) lipids are associated at the starch granule surface, and, if so, how they interact with the starch granule surface itself. Starch was isolated from a soft wheat cultivar containing both wild-type PINs and incubated with peptidases or lipases, or in extraction media (typically used for defatting). Protein, PIN, and lipid levels revealed that PINs and lipids are tightly associated together at the starch granule surface. Our results imply that PINs need lipids for binding to the granule surface but not vice versa.

The impact of steeping, germination and hydrothermal processing of wheat (Triticum aestivum L.) grains on phytate hydrolysis and the distribution, speciation and bio-accessibility of iron and zinc elements

Chelation of iron and zinc in wheat as phytates lowers their bio-accessibility. Steeping and germination (15 °C, 120 h) lowered phytate content from 0.96% to only 0.81% of initial dry matter. A multifactorial experiment in which (steeped/germinated) wheat was subjected to different time (2-24 h), temperature (20-80 °C) and pH (2.0-8.0) conditions showed that hydrothermal processing of germinated (15 °C, 120 h) wheat at 50 °C and pH 3.8 for 24 h reduced phytate content by 95%. X-ray absorption near-edge structure imaging showed that it indeed abolished chelation of iron to phytate. It also proved that iron was oxidized during steeping, germination and hydrothermal processing. It was further shown that zinc and iron bio-accessibility were respectively 3 and 5% in wheat and 27 and 37% in hydrothermally processed wheat. Thus, hydrothermal processing of (germinated) wheat paves the way for increasing elemental bio-accessibility in whole grain-based products.

Pearling Affects the Lipid Content and Composition and Lipase Activity Levels of Wheat (Triticum aestivum L.) Roller Milling Fractions

Wheat bran contains most of the dietary fiber, vitamins, minerals, and antioxidants of the grain. Unfortunately, it readily deteriorates upon storage because it has high lipid contents and lipase activity levels, which can cause rancidity and, hence, when used in food systems, inferior product quality. We here examined the lipid composition and the lipase activities of wheat bran and the impact of pearling prior to milling thereupon. The lipid content of the outer bran layers (2.31% on a dry matter [dm] basis) is lower than that of regular bran (3.81% dm). Nevertheless, these layers have the highest concentration of free fatty acids (FFA, 0.56% dm), which is ascribed to lipid hydrolysis. Indeed, the lipase activity levels in the peripheral layers were three times higher than in the bran itself. Abrading these tissues by pearling prior to milling yielded a bran fraction with about 30% lower FFA content and 30% lower lipase activity level. Pearling offers opportunities to lower the FFA content and lipase ac...