Collaborative Analysis of Wheat Endosperm Compressive Material Properties

Abstract

Cereal Chem. 88(4):391-396The objective measurement of cereal endosperm texture, for wheat (Triticum spp. L.) in particular, is relevant to the milling, processing, and utilization of grain. The objective of this study was to evaluate the interlaboratory results of compression failure testing of wheat endosperm specimens of defined geometry. Parallelepipeds (bricks) and cylinders were prepared from individual soft and hard near-isogenic wheat kernels and compressed in two orientations (parallel and perpendicular to the long brush-to-germ axis). Compression curves were used to derive failure stress, failure strain, work density (area under the curve), and Young's modulus. In all five laboratories, the ability to delineate hard from soft wheat endosperm material properties was quite high. Four laboratories compressed endosperm bricks in the same orientation, on edge; texture class (soft vs. hard) was consistently the greatest source of variation in analysis of variance models (F-values from 417 to 1401, Young's modulus and failure stress, respectively). Failure stress was found to be the best overall means of measuring the difference in what is known in the vernacular as wheat hardness. Across laboratories, the absolute measures of all four material properties ranged on the order of about twoto threefold from low to high, although within a laboratory, results were highly consistent. Laboratory by texture class interaction was deemed to be of minor importance. Brick size and moisture content within the ranges tested were not major sources of variation, and cylinders prepared from endosperm produced results similar to those obtained from bricks. The results suggested that wheat endosperm might express some level of anisotropic behavior, as specimens compressed in the kernel orientation parallel to the long axis failed at lower strain and stress values, with lower work density, when compared with kernel orientation perpendicular to the long axis. A key feature of interlaboratory variation was identified as being instrument rigidity, a subject of ongoing research. In conclusion, the preparation of endosperm specimens of defined size and shape, in combination with compression failure testing at low moisture content (<18%), is useful for objectively delineating the phenomenon known as hardness. The study presented here will advance our ability to objectively measure cereal grain texture and the material properties of endosperm.

Effect of Moisture Content on the Viscoelastic Properties of Individual Wheat Kernels Evaluated by the Uniaxial Compression Test Under Small Strain

“…However, the characteristics of the individual kernels within the sample are lost. Several studies have used this focus, with the authors reporting interesting findings about the texture and rheological properties of cylindrical, cubic, parallelepiped, and brick endosperm specimens in compression tests (Glenn et al 1991;Kang et al 1995;Haddad et al 1999Haddad et al , 2001Delwiche 2000;Dobraszczyk et al 2002;Samson et al 2005;Wang and Jeronimidis 2008;Morris et al 2011;Delwiche et al 2012).…”

Development of soft kernel durum wheat

“…Regarding crushing strength, the most fundamental approach involves preparing a specimen of defined dimensions and applying a stress until the specimen fails. Typical response variables include failure stress, failure strain, failure energy (area), and Young's modulus [12][13][14][15][16] . Specimens may be parallelepipedal ("brick") or cylindrical.…”

Influence of Instrument Rigidity and Specimen Geometry on Calculations of Compressive Strength Properties of Wheat Endosperm

“…At Montpellier, six soft and six hard brick-like specimens were prepared according to the procedure of Haddad et al (1998). Additional details are found in Morris et al (2011).…”

“…From the third cause, it is apparent that hard wheats, because of their greater capacity to withstand external force, will be affected more than will soft wheats. Procedure Bricks and cylinders were tested one at a time, as described in detail by Morris et al (2011). Briefly, the specimens were compressed until failure, with recordings made of apparent displacement and force at sampling frequencies noted previously.…”