Abstract: In order to understand the relationship of aril breakdown with energy levels and cell wall metabolism in harvested grapes, the ultrastructural changes in the inner pericarp were examined during the early and late stages of storage. ‘Red globe’ grapes were subjected to CaCl2 immersion combined with chitosan coating or heat treatment and then stored at (4.0 ± 0.5) ℃, and the untreated samples were used as a control. Changes in aril breakdown index, hardness, decay percentage, cell membrane permeability, energy contents (adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP)), energy charge (EC), cell wall-degrading enzyme activities and cell wall components were monitored at regular intervals during storage. The results indicated that aril breakdown index, decay incidence and cell membrane permeability increased, hardness and energy contents declined, and the activities of the cell walldegrading enzymes polygalacturonase (PG), pectinesterase (PE) and cellulase (Cx) ascended with storage time; however, β-galactosidase (β-Gal) activity dropped during the first 30 days, followed by a sharp increase. The contents of cell wall components such as protopectin, cellulose and semi-cellulose continuously decreased during storage, while water-soluble pectin dropped after an initial increase. Furthermore, the ultrastructure of the inner pericarp was damaged as indicated by the appearance of large holes. Aril breakdown index showed a highly significant inverse correlation with ATP and ADP contents and the contents of cell wall components (P < 0.01), a highly significant positive correlation with PG, PE and Cx activities (P < 0.01), and a significant inverse correlation with AMP level (P < 0.05), but it had no significant correlation with EC or β-Gal activity (P > 0.05). In conclusion, combined treatment with calcium chloride and chitosan or heat could delay aril breakdown in grapes by maintaining the integrity of the cell membrane and high energy status, inhibiting the transformation of protopectin to water-soluble pectin, inhibiting the activities of cell wall-degrading enzymes (PG, PE and Cx), and suppressing the degradation of cell wall components (proto-pectin, cellulose and semi-cellulose), and chitosan coating was significantly more effective than heat treatment (P < 0.05).

Key words: grape fruit, aril breakdown, energy levels, ultrastructure, cell wall metabolism