1-MCP application in 'Xuxiang' kiwifruit at appropriate firmness avoids hard-core and prolongs the shelf life

The lack of synchrony in softening among the tissue zones and the increase in the production of autocatalytic ethylene lead to the hard-core and a short eating window in ready-to-eat kiwifruit. The present study analyzed the differences between the outer pericarp and the core during ripening to identify the cause of hard-core in 'Xuxiang' kiwifruit and aimed to maintain a soft texture and extend the eating window of ready-to-eat kiwifruit using 1-methylcyclopropene (1-MCP). Initial analysis showed that the outer pericarp had a few small spherical cells and many elongated cells, while the core had large homogeneous parenchyma cells. The core maintained higher firmness and cell wall polysaccharide content than the outer pericarp. During ripening, the pericarp followed a sigmoidal trend in softening, while the core followed a linear trend. We also found that the outer pericarp preceded the core in expressing the cell wall degradation-related and ethylene biosynthesis-related genes (AcXET1, AcEXP1, AcPG, AcPL2, AcACS1, and AcACO2). Moreover, the increase in ethylene production was highly correlated with the decrease in core firmness. These differences between the outer pericarp and the core probably led to the hard-core in kiwifruit. Subsequent texture analysis and sensory evaluation revealed 75-100 N as the acceptable core firmness limit for 'Xuxiang' kiwifruit. The fruit treatment experiments based on these observations showed that applying 1-MCP on ready-to-eat 'Xuxiang' kiwifruit at similar to 12 N firmness resulted in best preservation, with an extra 15 d of shelf life and an acceptable core firmness. In conclusion, these findings suggest that treating 'Xuxiang' kiwifruit at similar to 12 N firmness after harvest with 1-MCP will help avoid hard-core and prolong the eating window, improving consumer acceptance.