The effects of CO₂ and 1-methylcyclopropene (1-MCP) on the uniform softening of 'Hayward' kiwifruit

Kiwifruit (Actinidia deliciosa) is harvested when mature but unripe, and needs to ripen before consumption. During ripening, dramatic changes occur in its texture and sweetness. However, the rates of these changes may be distinctly different in the pericarp and core. As the rate of fruit ripening is affected by environmental postharvest conditions, such as temperature, storage atmosphere and exposure to ethylene or to the ethylene action inhibitor 1-methylcyclopropene (1-MCP), we examined the response of the pericarp and core tissues to these factors. ‘Hayward’ kiwifruit was stored for five months at -0.5°C in controlled atmospheres with different concentrations of CO₂ (5 or 3%) at 2% O₂, with or without previous exposure to 1-MCP. Ripening during storage was monitored by periodically assessing firmness and total soluble solids (TSS) in the pericarp and core tissues. Ethylene production by the intact fruit was measured upon removal from storage. Despite different rates of softening among treatments, the firmness ratio between the core and pericarp during the first three months of storage remained constant at ~2. During the subsequent two months, the pericarp softened more rapidly than the core and differences among treatments began to appear. Although CO₂ contributed to maintaining the firmness of fruit not treated with 1-MCP, the pericarp softened more rapidly than the core at 3% CO₂ and the lack of uniform softening was significantly greater than at 5% CO₂. Treatment with 1-MCP delayed softening of both tissues markedly during storage irrespective of CO₂, and the loss in uniformity of softening after three months’ storage was less, similar to that of fruit stored in 5% CO₂ without 1-MCP. TSS initially increased more rapidly in the core than in the pericarp, but after four months’ storage there was no difference between the tissues and no effect of the treatments was observed.