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Mechanical Properties of Wheat Seed Coats

¹Unité de Technologie des Céréales et des Agropolymères, INRA-ENSAM. 2, Place Viala. 34060 Montpellier Cedex 01, France. Fax: (33) 4 67 52 20 94; Email: mabille@ensam.inra.fr ²Laboratoire de Mécanique et génie civil, Cc. 081, Université Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, France. Fax: (33) 4 67 14 34 83.

The crumbliness of starchy endosperm and the resistance of bran are key characteristics that enhance milling behavior of wheat and are dependent on the genetic origin and moisture content of the grain. A method was developed to measure the mechanical properties of bran samples based on the measurement of tensile stress and strain. Tests conducted with this highly reproducible and sensitive method documented cultivar and moisture-content effects (6.3, 13.8, and 18%, wb) on rheological behavior of wheat seed coats. A moisture-dependent reduction in stress to fracture (-15 to -30%) and in Young's modulus (-45 to -55%) was quantified. An increase in deformation to fracture of seed coats was also correlated with bran size differences after milling. The energy required to fracture a sample (from 0.4 to 1.3 J/mm³) was considered the most valid of all presented parameters for assessing the milling behavior of wheat seed coats and the size of bran fractions.