Mechanical modeling of wheat hardness and fragmentation

The mechanical origin of the wheat hardness used to classify wheat flours is an open issue. We propose a cohesive granular model of wheat endosperm involving a discrete phase composed of starch granules, a continuous phase representing the protein matrix, and pores. A lattice element method is employed to simulate the behavior of numerical samples with variable matrix volume fraction and starch–protein adherence subjected to axial tension and compression. We show that the effective stiffness is a linear function of matrix volume fraction but is higher in compression than in tension. Crack formation is analyzed in terms of particle damage as a function of matrix volume fraction and particle-matrix adherence. Our data provide evidence for three regimes of crack propagation depending on the crack path through the material. These regimes are associated with the three hardness classes of soft, hard and durum wheat. We also show that starch damage scales well with the relative toughness of the starch–protein interface. The interface toughness appears therefore to be strongly correlated with particle damage and determines transition from soft to hard behavior.