Compressive Strength of Wheat Endosperm: Analysis of Endosperm Bricks

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 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.

Compressive Strength of Wheat Endosperm: Comparison of Endosperm Bricks to the Single Kernel Characterization System

“…The whole model was highly significant (F = 42.9) and explained 73% of the total variation (R 2 ) in SKCS HI among n = 150 individual kernels. This model fit was similar to those obtained in the brick study (Morris et al 2008), wherein whole model R 2 for failure strain, failure stress, and failure energy was 68-79%. Coefficients of variation (CV) were 24.0% for failure strain, 21.3% for failure stress, 43.5% for failure energy, and 23.3% for SKCS.…”

“…We next examined the brick material property data from our previous study. In that study (Morris et al 2008), failure stress and failure energy were highly correlated (r = 0.94) and Young's modulus bore little relationship to known texture classes. Therefore, only failure strain and failure energy will be included here.…”

“…We began this research with the question of whether the kernelto-kernel variation observed in the SKCS HI was due to variation of the wheat endosperm itself or rather was attributable in whole or in part to the SKCS technique (which includes the geometry and hetero-morphology of the kernel, and the mechanics of crushing and interpreting the crush data). Based on this and the preceding study (Morris et al 2008), the general conclusion is that within the limits of current compression tests of endosperm bricks of defined dimension and geometry, kernel-to-kernel and withinkernel variability will preclude a dramatic reduction in SKCS HI variation.…”

“…8 shows that for soft wheat grain sublots (each variety sorted according to vitreous and mealy kernels), the SKCS provided some separation (26.2-41.8 HI), whereas the failure energies of each fell within a relatively narrow range (2.5-5.9 MJ/m 3 ). SKCS provided a large separation between the soft and hard texture market classes (41.8-69.9 HI), whereas the failure energies between the hardest soft wheat sample/kernel type (Madsen vitreous, 5.9 MJ/m 3 ) and the softest hard wheat sample (hard Alpowa mealy, 8.1 MJ/m 3 ) were quite similar (in fact, not significantly different) (Morris et al 2008). Conversely, the SKCS grouped the hard and durum wheat samples into a narrower range than did failure energy.…”

“…Interpretation of the results presented here required some subjective assessment. Descriptive statistics from ANOVA suggested that variation was similar among SKCS and KS-brick compression tests (Morris et al 2008) (Table I). Frequency distribution plots provided a similar conclusion (Figs.…”

Compressive Strength of Wheat Endosperm: Comparison of Endosperm Bricks to the Single Kernel Characterization System

“…The whole model was highly significant (F = 42.9) and explained 73% of the total variation (R 2 ) in SKCS HI among n = 150 individual kernels. This model fit was similar to those obtained in the brick study (Morris et al 2008), wherein whole model R 2 for failure strain, failure stress, and failure energy was 68-79%. Coefficients of variation (CV) were 24.0% for failure strain, 21.3% for failure stress, 43.5% for failure energy, and 23.3% for SKCS.…”

“…We next examined the brick material property data from our previous study. In that study (Morris et al 2008), failure stress and failure energy were highly correlated (r = 0.94) and Young's modulus bore little relationship to known texture classes. Therefore, only failure strain and failure energy will be included here.…”

“…We began this research with the question of whether the kernelto-kernel variation observed in the SKCS HI was due to variation of the wheat endosperm itself or rather was attributable in whole or in part to the SKCS technique (which includes the geometry and hetero-morphology of the kernel, and the mechanics of crushing and interpreting the crush data). Based on this and the preceding study (Morris et al 2008), the general conclusion is that within the limits of current compression tests of endosperm bricks of defined dimension and geometry, kernel-to-kernel and withinkernel variability will preclude a dramatic reduction in SKCS HI variation.…”

“…8 shows that for soft wheat grain sublots (each variety sorted according to vitreous and mealy kernels), the SKCS provided some separation (26.2-41.8 HI), whereas the failure energies of each fell within a relatively narrow range (2.5-5.9 MJ/m 3 ). SKCS provided a large separation between the soft and hard texture market classes (41.8-69.9 HI), whereas the failure energies between the hardest soft wheat sample/kernel type (Madsen vitreous, 5.9 MJ/m 3 ) and the softest hard wheat sample (hard Alpowa mealy, 8.1 MJ/m 3 ) were quite similar (in fact, not significantly different) (Morris et al 2008). Conversely, the SKCS grouped the hard and durum wheat samples into a narrower range than did failure energy.…”

“…Interpretation of the results presented here required some subjective assessment. Descriptive statistics from ANOVA suggested that variation was similar among SKCS and KS-brick compression tests (Morris et al 2008) (Table I). Frequency distribution plots provided a similar conclusion (Figs.…”

Compressive Strength of Wheat Endosperm: Comparison of Endosperm Bricks to the Single Kernel Characterization System

“…The whole model was highly significant (F = 42.9) and explained 73% of the total variation (R 2 ) in SKCS HI among n = 150 individual kernels. This model fit was similar to those obtained in the brick study (Morris et al 2008), wherein whole model R 2 for failure strain, failure stress, and failure energy was 68-79%. Coefficients of variation (CV) were 24.0% for failure strain, 21.3% for failure stress, 43.5% for failure energy, and 23.3% for SKCS.…”

“…We next examined the brick material property data from our previous study. In that study (Morris et al 2008), failure stress and failure energy were highly correlated (r = 0.94) and Young's modulus bore little relationship to known texture classes. Therefore, only failure strain and failure energy will be included here.…”

“…We began this research with the question of whether the kernelto-kernel variation observed in the SKCS HI was due to variation of the wheat endosperm itself or rather was attributable in whole or in part to the SKCS technique (which includes the geometry and hetero-morphology of the kernel, and the mechanics of crushing and interpreting the crush data). Based on this and the preceding study (Morris et al 2008), the general conclusion is that within the limits of current compression tests of endosperm bricks of defined dimension and geometry, kernel-to-kernel and withinkernel variability will preclude a dramatic reduction in SKCS HI variation.…”

“…8 shows that for soft wheat grain sublots (each variety sorted according to vitreous and mealy kernels), the SKCS provided some separation (26.2-41.8 HI), whereas the failure energies of each fell within a relatively narrow range (2.5-5.9 MJ/m 3 ). SKCS provided a large separation between the soft and hard texture market classes (41.8-69.9 HI), whereas the failure energies between the hardest soft wheat sample/kernel type (Madsen vitreous, 5.9 MJ/m 3 ) and the softest hard wheat sample (hard Alpowa mealy, 8.1 MJ/m 3 ) were quite similar (in fact, not significantly different) (Morris et al 2008). Conversely, the SKCS grouped the hard and durum wheat samples into a narrower range than did failure energy.…”

“…Interpretation of the results presented here required some subjective assessment. Descriptive statistics from ANOVA suggested that variation was similar among SKCS and KS-brick compression tests (Morris et al 2008) (Table I). Frequency distribution plots provided a similar conclusion (Figs.…”

Compressive Strength of Wheat Endosperm: Comparison of Endosperm Bricks to the Single Kernel Characterization System

“…The whole model was highly significant (F = 42.9) and explained 73% of the total variation (R 2 ) in SKCS HI among n = 150 individual kernels. This model fit was similar to those obtained in the brick study (Morris et al 2008), wherein whole model R 2 for failure strain, failure stress, and failure energy was 68-79%. Coefficients of variation (CV) were 24.0% for failure strain, 21.3% for failure stress, 43.5% for failure energy, and 23.3% for SKCS.…”

“…We next examined the brick material property data from our previous study. In that study (Morris et al 2008), failure stress and failure energy were highly correlated (r = 0.94) and Young's modulus bore little relationship to known texture classes. Therefore, only failure strain and failure energy will be included here.…”

“…We began this research with the question of whether the kernelto-kernel variation observed in the SKCS HI was due to variation of the wheat endosperm itself or rather was attributable in whole or in part to the SKCS technique (which includes the geometry and hetero-morphology of the kernel, and the mechanics of crushing and interpreting the crush data). Based on this and the preceding study (Morris et al 2008), the general conclusion is that within the limits of current compression tests of endosperm bricks of defined dimension and geometry, kernel-to-kernel and withinkernel variability will preclude a dramatic reduction in SKCS HI variation.…”

“…8 shows that for soft wheat grain sublots (each variety sorted according to vitreous and mealy kernels), the SKCS provided some separation (26.2-41.8 HI), whereas the failure energies of each fell within a relatively narrow range (2.5-5.9 MJ/m 3 ). SKCS provided a large separation between the soft and hard texture market classes (41.8-69.9 HI), whereas the failure energies between the hardest soft wheat sample/kernel type (Madsen vitreous, 5.9 MJ/m 3 ) and the softest hard wheat sample (hard Alpowa mealy, 8.1 MJ/m 3 ) were quite similar (in fact, not significantly different) (Morris et al 2008). Conversely, the SKCS grouped the hard and durum wheat samples into a narrower range than did failure energy.…”

“…Interpretation of the results presented here required some subjective assessment. Descriptive statistics from ANOVA suggested that variation was similar among SKCS and KS-brick compression tests (Morris et al 2008) (Table I). Frequency distribution plots provided a similar conclusion (Figs.…”