X-ray photoelectron spectroscopy for wheat powders: measurement of surface chemical composition.

The functional properties of wheat powders depend largely on the surface characteristics of their particles. X-ray photoelectron spectroscopy (XPS) has been considered to investigate the surface composition of wheat powders. The objective of the present study is to evaluate the ability of XPS to discriminate wheat components and to calculate the surface composition of wheat powders. First, XPS surveys for the main wheat isolated components (starch, proteins, arabinoxylans, and lipids) were determined. XPS results demonstrate that it is able to distinguish wheat proteins, polysaccharides, and lipids, but it is not able to distinguish starch and arabinoxylan because of their similarity in chemical structure. The XPS analyses of simple reconstituted wheat flours based on two components (starch and protein) or three components (by adding arabinoxylan) demonstrated the ability of XPS to measure the surface composition of the wheat flours. The surface composition of native wheat flour demonstrated an overrepresentation of protein (54%) and lipids (44%) and an underrepresentation of starch (2%) compared to the bulk composition. Results are discussed with regard to difficulties in discriminating arabinoxylans and starch components.