Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2008
Publication Date: 6/18/2008
Citation: Morris, C.F., Pitts, M.J., Bettge, A.D., Pecka, K., King, G.E., Mccluskey, P.J. 2008. The compressive strength of wheat endosperm: Analysis of endosperm 'bricks'. Cereal Chemistry 85(3):351-358. Interpretive Summary: An understanding of wheat kernel hardness (texture) is important for determining the processing and end-use quality of wheat. A previously developed device was used to prepare tiny brick-shaped specimens from the endosperm of individual kernels of wheat. These bricks were subjected to compression testing. Material engineering properties were analyzed. Results indicated distinct differences among soft, hard, and durum wheats. Although highly reproducible, measurements often differed from those reported elsewhere.
Technical Abstract: The material properties of wheat grain endosperm are central to its processing and end-use quality. The preparation of geometrically-defined endosperm specimens free of bran, germ, and pigment strand can facilitate the objective study of endosperm material properties. This study was conducted to characterize the material properties of wheat endosperm from two soft, two hard, and one durum wheat varietal samples. Additionally, each varietal sample was sorted according to vitreous or mealy kernel type. Endosperm ‘bricks’ approximately 0.76 ' 2.08 ' 1.06 mm were prepared using an abrading (‘Kernel Sanders, KS’) device. Bricks were tested in compression using a TA.XTPlus. Stress-strain curves were used to calculate failure strain, failure stress, failure energy, and Young’s Modulus. Additionally, the effect of brick ‘aging’ up to one month, and changes in moisture content (freeze-drying, oven drying, and equilibration to approximately 10.5-11% m.c.) were studied. Intra-kernel variation was assessed by preparing ‘sibling’ bricks (2, one from each cheek) from individual kernels. Failure strain, stress, and energy all had relatively high model R2’s (0.68, 0.79, and 0.75, respectively). The ANOVA model R2 for Young’s Modulus was 0.46. All models indicated variety as a highly significant source of variation in brick material properties. The effect of vitreous vs. mealy kernel type was not consistent across varietal samples. Brick ‘age’ and moisture content did not significantly affect brick material properties. Analysis of sibling bricks indicated that the magnitude of intra-kernel variation was similar to that observed for individual varietal lots of uniform vitreous or mealy kernel type. Overall, failure strain provided a ranking and mean separation most consistent with kernel texture market class. The results obtained in the present study, although similar to, do not closely agree with other published reports on the material properties of wheat endosperm. Similarly, published results of material properties often differ by several-fold. The source of these discrepancies are at present unknown, but in some circumstances may relate to specimen orientation relative to the source kernel as there was evidence for anisotropic behavior. A companion study compares the variation in kernel texture obtained with the Single Kernel Characterization System with that obtained here using bricks.