Development of the cuticular membrane and biomechanical properties in Hupingzao (Ziziphus jujuba Mill. 'Hupingzao')

During the development of the jujube fruit, cracking can occur. This is due to physiological disease and can cause huge economic losses. Analyzing changes in the cuticular membrane (CM) and mechanical properties during the jujube fruit development can clarify the relationship between the characteristics of the CM and cracking. This study used Hupingzao (Ziziphus jujuba Mill. 'Hupingzao') to examine the development of CM and the biomechanical properties of the fruit through enzymatic hydrolysis and a puncture test. The results showed that the mass of the CM per unit fruit surface area gradually increased and CM mass per unit area in the shoulder region was always higher during the fruit development process. After the white-ripe period, cracks appeared in the waxy layer on the surface of the pericarp and the shoulders mainly had transverse cracks. And the cuticle structure was loose. Pericarp break force, pericarp break distance and pericarp toughness showed a negative correlation to the CM mass per unit area. The pericarp break force, pericarp toughness and pericarp brittleness stopped decreasing and started increasing in the white-ripe period. The differences in the biomechanical properties among the three regions of the fruit increased during the coloring period. In the coloring period, the pericarp break force and pericarp brittleness were significantly lower in the fruit shoulder and top regions than in the fruit cheek region. However, the pericarp break distance was significantly higher in the fruit shoulder and top regions than in the fruit cheek region.