Compressive Strength Of Endosperm Bricks with TA.XTPlus Texture Analyzer

A very important series of articles were recently published in AACC International's Cereal Chemistry. The series introduced a technique to standardize the measurement of the compressive strength of wheat grain endosperm. The method's importance is that it presents a method to neutralize the impact (and variability) of grain geometry and genotype from the hardness test. For the first time a hardness method is available that allows direct cross comparison of many different types of grains and cereals.

A Device for the Preparation of Cereal Endosperm Bricks
Craig F. Morris, Kameron Pecka, and Arthur D. Bettge
Cereal Chem. 84(1):67–69

Compressive Strength of Wheat Endosperm: Analysis of Endosperm Bricks
Craig F. Morris, Marvin J. Pitts, Arthur D. Bettge, Kameron Pecka, Garrison E. King, and Patrick J. McCluskey
Cereal Chem. 85(3):351–358

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 kerneltexture 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.

ABSTRACT: The three major classes of endosperm texture (grain hardness) of soft and hard common, and durum wheat represent and define one of the leading determinants of the milling and end-use quality of wheat. Although these three genetic classes are directly related to the Hardness locus and puroindoline gene function, much less is known about the kernel-tokernel variation within pure varietal grain lots. Measurement of this variation is of considerable interest. The objective of this research was to compare kernel texture as determined by compression failure testing using endosperm bricks with results of whole-kernel hardness obtained with the Single Kernel Characterization System 4100 hardness index (SKCS HI). In general terms, the variation obtained with the SKCS HI was of similar magnitude to that obtained using failure strain and failure energy of endosperm brick compression. Objective comparisons included frequency distribution plots, normalized frequency distribution plots, ANOVA model R2, and coefficients of variation. Results indicated that compression testing and SKCS HI similarly captured the main features of texture classes but also reflected notable differences in texture properties among and within soft, hard, and durum classes. Neither brick compression testing nor the SKCS HI may be reasonably expected to correctly classify all individual kernels as to genetic texture class. However, modest improvements in correct classification rate or, more importantly, better classification related to end-use quality may still be achievable.

These articles are in the public domain may be freely reprinted with customary proper crediting of Cereal Chemistry and the AACC International, Inc.