Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2010
Publication Date: 9/8/2010
Publication URL: http://hdl.handle.net/10113/45262
Citation: Scudiero, L., Morris, C.F. 2010. Scanning electron and atomic force microscopy, and raman and x-ray photoelectron spectroscopy characterization of near-isogenic soft and hard wheat kernels and corresponding flours. Journal of Cereal Science 52:136-142. Interpretive Summary: Kernel hardness is a fundamental property of wheat grain. In hexaploid wheat two texture classes are recognized and are referred to as ‘hard’ and ‘soft’. This distinction is included in most marketing systems around the world as it influences many aspects of milling, flour particle size, starch damage, and processing properties. The mechanism by which puroindolines soften kernels is essentially unknown. What is known is that soft and hard wheat endosperms differ in their material properties as evidenced by failure stress, failure strain and failure energy. These differences are ascribed to differences in adhesion between cell constituents, namely starch granules and protein matrix, and possibly cell walls. Currently, powerful technologies such as atomic force microscopy, Raman and X-ray photoelectron spectroscopy (XPS) are available to study this important phenomenon. The examination of endosperm from soft and hard wheat kernels with these technologies has not heretofore been attempted. Although atomic force microscopy (AFM) is a powerful tool to characterize flat surfaces without special preparation from the micrometer to the nanometer scale, it has not been used extensively in food science research. Its utilization has been growing rapidly, with studies of rheology in food biopolymers, the surface of starch granules surfaces of barley, corn, maize and pea starch . It has also been used to image bacteria and the skin of peaches. We used the AFM in this work to analyze the endosperm of (the starchy interior of the grain) surface of vitreous and non-vitreous gentically near-isogenic soft and hard wheat kernels. The surface morphology provides some insight as to the differences between these two kernels types, and therefore some insight to the puroindolines, kernel texture, grain size and distribution.
Technical Abstract: Atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to investigate vitreous (hard) and non-vitreous (soft) wheat kernels and their corresponding wheat flours. AFM data reveal two different microstructures. The vitreous kernel reveals a granular texture with distinct individual starch granules having sizes ranging from 10 to 50 nm across while the images obtained for the non-vitreous kernel display less distinct small grains and more large features, clusters of starch granules. Raman spectra resolved five distinct frequencies for both kernels with however slightly different intensities. Finally, the chemical surface compositions of flour for these two types of kernels obtained by XPS provide subtle insight into the differences between hard and soft grains. The concentration of carbon and nitrogen is slightly lower for the soft wheat while the amount of oxygen is higher for the soft than for the hard wheat.