Internal bruising prediction in watermelon compression using nonlinear models

Fruit bruising could occur during handling, transportation and storage. It is invisible in many cases of fruits such as watermelon. In this study, nonlinear finite element analysis (FEA) was used to investigate internal bruising in watermelon compressed in longitudinal and transverse directions by parallel plates. The applied forces on models were equal to 10% of breaking force or 152 N and 92 N, respectively for Crimson sweet and Charleston gray varieties in the longitudinal direction. The simulation results show that equivalent stresses in the red flesh are higher than the failure stress in both varieties (27 kPa and 37 kPa for Crimson sweet and Charleston gray, respectively). However, the maximum equivalent stresses located near the surface of watermelon are well below the failure stresses of rind (1.2 MPa and 1.1 MPa for Crimson sweet and Charleston gray, respectively). This indicates that the bruise of the red flesh is the primary form of mechanical damage of watermelons under compression in both directions. The nonlinear FEA data confirmed well experimental results and has the ability to predict bruising in watermelons under different load conditions.