Postharvest osmotic dehydration of pedicels of sweet cherry fruit

The appearance of the pedicels is a good indicator of postharvest freshness of sweet cherry fruit (Prunus avium L.). Shrivelled pedicels are thought to result from water loss due to pedicel transpiration after extended periods of storage or after storage under inferior (drying) conditions. This study establishes that osmotic dehydration can also be a factor in pedicel deterioration during storage. A time course study revealed that the water content of a pedicel attached to its fruit and incubated at 100% relative humidity (RH) decreased within 24 h and remained approximately constant thereafter. In contrast, the water content of a detached pedicel, increased slightly and continuously over nine days. Similarly, pedicel diameter decreased when a pedicel remained attached to its fruit but did not decrease when it was detached. Pedicels that remained attached to their fruit yellowed more rapidly than the ones that had been detached. Pedicel dehydration was not related to pedicel transpiration, as this was effectively zero at 100% RH. The decrease in water content of attached pedicels was accompanied by a corresponding increase in osmolarity. However, the osmolarity of detached pedicels decreased slightly. Potometry revealed a continuous flow of water through the pedicel into the fruit even though the fruit was held under non-transpiring conditions (100% RH). When a fruit and pedicel was mounted on a pressure probe (100% RH), a slight negative pressure developed that gradually approached an equilibrium value of −30.3 ± 2.0 kPa. Our results demonstrate that osmotic dehydration accounts for pedicel shrivelling recorded at 100% RH.