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Compressive Strength of Wheat Endosperm: Analysis of Endosperm Bricks¹

¹This research was supported, in part, by a grant to the WWQL from the USDA GIPSA. Mention of trademark or proprietary products does not constitute a guarantee or warranty by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. ²USDA-ARS Western Wheat Quality Laboratory, Washington State University, Pullman, WA 99164-6394. ³Corresponding author. Phone: +1.509.335.4062. Fax: +1.509.335.8573. E-mail: morrisc@wsu.edu ⁴Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120. ⁵Currently, Leprino Foods, 2401 North MacArthur Drive, Tracy, CA 95376-2095. ⁶Department of Food Science & Human Nutrition, Washington State University, Pullman, WA 99164-6394. ⁷Assigned to the Western Wheat Quality Laboratory. ⁸USDA-GIPSA Federal Grain Inspection Service, Kansas City, MO 64133.

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 texture analyzer (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 ≈10.5–11% mc) were studied. Intrakernel variation was assessed by preparing two sibling bricks (one from each cheek) from individual kernels. Failure strain, stress, and energy all had relatively high model R² values (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 versus 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 intrakernel 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 other published reports do not closely agree with them on the material properties of wheat endosperm. Similarly, published results of material properties often differ considerably. The source of these discrepancies are at present unknown, but in some circumstances they 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 (SKCS) with that obtained here using bricks.