Abstract: Compression test and finite element method (FEM) simulation were conducted to investigate the compression properties of jujube fruits (Zizyphus jujuba Mill. cv. Dongzao) at different ripening stages. The study aimed at reducing mechanical damage at harvest and during postharvest sorting, transportation and storage. The elastic moduli and contact stress of jujubes harvested at the white maturity and crisp maturity stages were measured under compression in two directions. From the experiment data, it was observed that the rupture force of white maturity fruits was greater than that of crisp maturity fruits in both transverse and vertical compression directions. The force-deformation curves of white maturity and crisp maturity fruits were similar, with obvious bioyield point under transverse compression rather than under vertical compression. Under transverse compression, elastic modulus predicted by the standard established by the American Society of Agricultural Engineering (ASAE) was in agreement with that evaluated by FEM simulation. The average apparent elastic modulus of white maturity fruits predicted by the ASAE standard and evaluated by FEM simulation were 3.527 and 3.263 MPa, respectively with an average relative difference of 11.38%, while those of crisp maturity fruits predicted by the ASAE standard and evaluated by FEM simulation were 3.131 and 2.877 MPa, respectively with an average relative difference of 12.96%. However, there was a larger difference between the elastic modulus predicted by the ASAE standard and that determined through FEM simulation under vertical compression, which was 26.24% and 27.66% for white and crisp maturity fruits, respectively. These results can provide a theoretical basis for packaging design and stacking for transportation, grading and storage.

Key words: Dongzao jujube, compression properties, elastic modulus, finite element method