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Title: Collaborative analysis of wheat endosperm compressive material properties

item Morris, Craig
item Delwiche, Stephen - Steve
item Bettge, Arthur
item MABILLE, F - Institut National De La Recherche Agronomique (INRA)
item ABECASSIS, J - Institut National De La Recherche Agronomique (INRA)
item PITTS, M - Washington State University
item Dowell, Floyd
item DEROO, CAMILLE - Institute Polytechnique Lasalle Beauvais
item Pearson, Thomas

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2011
Publication Date: 8/12/2011
Citation: Morris, C.F., Delwiche, S.R., Bettge, A.D., Mabille, F., Abecassis, J., Pitts, M.J., Dowell, F.E., Deroo, C., Pearson, T.C. 2011. Collaborative analysis of wheat endosperm compressive material properties. Cereal Chemistry. 88:391-396.

Interpretive Summary: The hardness or texture of cereal grains is an important feature of how they are processed for foods and feeds, and imparts various properties of the resulting meals and flours, e.g. particle size distribution and starch damage. Wheat (Triticum spp. L.) is unique in that there are three defined hardness classes: soft and hard hexaploid wheat (T. aestivum), and very hard durum wheat (T. turgidum ssp. durum). Although there are a number of suitable methods to measure the texture of wheat grain, none provide absolute measures of true material properties. This paper reports on a multi-laboratory collaborative trial using a common source of wheat grains of defined texture genetics. Differences among labs due to testing protocols are indicated, endosperm bricks versus cylinders are compared, and the orientation of the specimen during compression is examined. Results are discussed in the context of machine rigidity, and specimen size, shape and orientation.

Technical Abstract: The objective measurement of cereal endosperm texture, for wheat (Triticum L.) in particular, is relevant to the milling, processing and utilization of grain. The objective of this study was to evaluate the inter-laboratory 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 germ-to-brush axis). Compression curves were used to derive failure stress, failure strain, work density (area under the curve), and Young’s Modulus. In all five labs, the ability to delineate hard from soft wheat endosperm material properties was quite high. Four labs compressed endosperm bricks in the same ‘on edge’ orientation; ‘texture class’ (soft vs. hard) was consistently the greatest source of variation in ANOVA models (F-values from 417 to 1401, Young’s Modulus and failure stress, respectively). Failure stress was found to be overall the best means of measuring the difference in what is known in the vernacular as “wheat hardness”. Across labs, the absolute measures of all four material properties ranged on the order of about 2-3 fold from low to high, although within a lab results were highly consistent. Lab 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 gave similar results. The results suggested that wheat endosperm does express some level of anisotropic behavior, as specimens compressed in the parallel-to-long axis orientation failed at lower strain and stress values, with lower work density. In conclusion, the preparation of endosperm specimens of defined size and shape, in combination with compression failure testing, is useful for objectively characterizing the material properties of wheat grain, especially the phenomenon known as “hardness”. ‘Universal’ agreement among labs for absolute values was not observed; improvement in inter-lab agreement will require further studies.