Human mastication of cereal based products can be regarded as a complex mechanical process leading to food breakdown. This first step is worth studying because of its importance for the other digestion steps. Understanding the mastication process depends on our ability to address fracture mechanisms that are associated to food breakdown. In this regard, the process of fragmentation during food mastication is investigated by the Discrete Element Method (DEM). The deflection of a crack by a pore is first simulated in a dense vitreous biopolymer. This case is used to fit the microscopic stiffness and the fracture criteria by comparing simulation results to experimental data on dense starch. The deflection of the crack is satisfactorily predicted. In a second stage, DEM is used to address the fragmentation process of a cellular biopolymer under simple compression. Numerical results are discussed based on the influence of the cellular structure on the fragment size distribution.