Berry dropping or shattering is an important factor during the harvest and post-harvest handling of fresh eating grapes until they reach the supermarkets. There are a lot of methods to measure post-harvest placing damage and the detachment force for single fruits. However, until now, there has been no objective method to observe and analyze the berry dropping mechanism of cluster fruits during robotic post-harvest handling. Therefore, in this paper, the effect of a cluster’s vibration on berry drop during vertical transportation and the impact of different packaging materials on fresh grape clusters during robotic placing were analyzed. For this purpose, a lead screw lathe, along with an attached actuator, three grape cluster samples (0.48, 0.50, 0.53 kg), three packaging materials (rigid plastic box, corrugated fiberboard box, expandable polystyrene box), four transportation speeds (0.4, 0.6, 0.8, 1.0 m/s), and four acceleration excitations (6, 8, 10, 12 m/s²) that were given in a mechanical system (actuator) were studied. In order to analyze the berry drop mechanism of grape clusters before and after the impact with packaging material, a force sensor and high-speed video camera were used. It was concluded from the vertical transportation test that with the increase in speed and acceleration excitations, the change in hanging force increased positively (R² = 0.92). Additionally, the force after the striking of the grape cluster with packaging materials decreased negatively (R² = 0.97), and the corresponding index of berry deflection increased. It was also observed from the high-speed camera images that rigid plastic boxes caused the maximum deflection of the grape berries, with the highest change in force of 8.6 N after the impact. Experimental results showed a negative correlation between the hanging force signals and the force after impact of the cluster, with a goodness of fit of R² = 0.95 at different speeds. Overall, the proposed findings can be used as a reference study for improving robotic post-harvest handling, providing a useful visual and technical understanding of the berry fall susceptibility of cluster fruits, and can be used to develop a post-harvest robotic placing tool for avoiding berry drop damage on both industrial and farm levels.

Mechanical stress induced by compression during preharvest and postharvest handling of fresh fruit is a major factor influencing the quality of fresh fruit. The degree of compression primarily governs the extent of quality deterioration. However, research on the damage mechanisms of mechanical compression in table grapes remains scarce. This investigation evaluated the impact of varying compression levels (0%, 20%, 40%, 60%, and 80%) on the postharvest quality attributes of table grapes. Changes in postharvest physical properties (overall appearance and color), structural properties (firmness, springiness, cohesiveness, and chewiness), physiological qualities (total soluble solids, titratable acidity, ascorbic acid, malonaldehyde content, and relative electrical conductivity), and cell microstructure of the berries was determined at 4 °C during 15 d of storage. Mechanical compression contributed to the deterioration of the quality of table grapes during storage, resulting in increased weight loss, decay rate, malonaldehyde content, and relative electrical conductivity; and decreased total soluble solids, titratable acidity, and ascorbic acid content. Furthermore, as compared to the control group, mechanical compression resulted in substantial yellowing and diminished textural qualities of grapes. In particular, compression treatment caused significant deformation of grape cell microstructure. In conclusion, mechanical compression stress significantly affects the physical and physiological properties of postharvest table grapes, as well as the internal cellular organization. As compression levels increase, the quality of table grapes progressively deteriorates, leading to a substantial reduction in storage life and commercial value. This study offers essential information for devising damage prevention strategies in preharvest and postharvest handling of table grapes.

Due to the fragility of table grapes, berries are prone to detachment during harvesting, transportation, and postharvest handling. This study aimed to clarify the effects of mechanical loading on the mechanical–physiological coupling process of berry detachment and to establish a predictive model for berry detachment percentage. In this study, the postharvest detachment mechanism of ‘Kyoho’ grapes was investigated by applying different levels of combined tensile–bending loads to the berry abscission zone. The results showed that combined tensile–bending stress accelerated the deterioration of visual quality and caused a marked decline in nutritional and flavor-related components. Furthermore, this stress altered respiration rate and endogenous hormone levels. In addition, combined tensile–bending loading increased the activities of cell wall-degrading enzymes, enhanced cell membrane permeability, and disturbed reactive oxygen species metabolism, with antioxidant enzyme activities in the abscission zone reaching their peaks earlier. Correlation analysis identified key physical and physiological indicators closely associated with berry detachment percentage. Physical–physiological indicators, mechanical loading level, and storage time were used as input variables, whereas berry detachment percentage was used as the output variable. Three predictive models, including multiple linear regression (MLR), back-propagation neural network (BPNN), and genetic algorithm-optimized BP neural network (GA-BP), were developed to predict berry detachment percentage. The results showed that the GA-BP model achieved higher prediction accuracy than the MLR and BPNN models, with R² = 0.9968 and RMSE = 1.5807. This study provides important insights into the mechanical–physiological coupling process underlying postharvest berry detachment in table grapes under mechanical loading. Moreover, the developed model may provide a useful tool for evaluating berry detachment risk during postharvest storage and transportation, thereby helping to improve quality management and extend shelf life.