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Study of Viscoelastic Properties of Wheat Kernels Using Compression Load Method

¹DIPA, Universidad Autónoma de Querétaro. Centro Universitario, Cerro de las Campanas S/N, Querétaro, Qro., CP 76010. ²Centro de Investigación y de Estudios Avanzados (CINVESTAV-IPN), Libramiento Norponiente 2000, Fracc. Real de Juriquilla, Querétaro, C.P. 76230 Qro., México. ³Corresponding author. E-mail: jfigueroa@qro.cinvestav.mx ⁴Facultad de Químico-Farmacobiología, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mich., México.

The method to measure hardness and other viscoelastic properties of intact wheat kernels is presented. Wheat with 9.3% moisture showed high elastic behavior compared with wheat tempered at 22.5% moisture that showed a plastic behavior. Load-deformation curves showed that bread wheat behaves as a more plastic material than durum wheat, which is a more elastic material. Yield point of all the wheat samples was ≈18.5 N, independent of wheat type and moisture content. The height of the wheat kernel increased linearly, and the compression area increased exponentially, with increasing moisture content. The modulus of elasticity of wheat ranged from 99.2 MPa for 22.5% moisture content to 394.8 MPa for 9.3% moisture content. Young's modulus range for soft wheat such as Salamanca, Saturno, and Cortazar cultivars was 232.2–308.5 MPa, as compared with Rayón bread wheat at 321.5 MPa and the Altar, Sofía, and Rafi cultivars of durum wheat that had elastic moduli of 438.7–485.8 MPa. The compression force and final stress decreased from 69.9 N and 40.1 MPa in soft wheat to 90 N and 78.9 MPa in durum, respectively. Total work range was 14.7 MPa/sec in soft wheat to 19.7 MPa/sec for durum wheat and, as expected, was higher in the durum and bread wheat than in soft wheat. The plastic part ranged from 2.4 MPa/sec in soft wheat to 0.6 MPa/sec in durum wheat.