Impacts of Fruit Frosting Coverage on Postharvest Softening of Prunes under Vibration Stress

The surface of prune fruit has a thick layer of frosting, which is easily damaged and lost during prunes harvest or postharvest handling, and there is no clear information on the effect of prune surface frost on postharvest storage quality. To investigate the effect of fruit frosting on the softening of prune fruits during storage under vibration stress, prunes were divided into three grades according to fruit frosting in this study and were vibrated for 8 h at a frequency of 5 Hz at 4 °C; then, samples were selected once every 8 d. The results showed that the heavy fruit frosting (HFF) group maintained higher hardness (21.47%), L* (20.85%), and total soluble solids (12.79%) levels at the end of storage and inhibited cell wall-modifying enzyme activities (polygalacturonase, pectin methylesterase, glycosidase, β-glucosidase, and cellulase) compared to frosting-less fruit (FF) group. This group also showed improved expression of key cell wall-modification genes (ADPG2, PME31, CESA1, BGAL3, XTH33, BGLU41) as well as chelate-soluble pectin (72.11%), Na₂CO₃-soluble pectin (42.83%), and cellulose (36.89%) solubilization and maintained lower water-soluble pectin (34.23%). Microscopic observations showed that the fruit frosting could delay the dissolution of pectin components and protect the cell wall structure. In summary, fruit frosting can effectively inhibit fruit softening and maintain fruit quality.