Postharvest osmotic dehydration of pedicels of sweet cherry fruit

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. dehydrated fruits

Plant materials

Mature, greenhouse- and field-grown sweet cherry fruit (Prunus avium L.) of the cvs ‘Frühe Rote Mecklenburger’, ‘Sam’ and ‘Regina’ were sampled from an experimental orchard of the Horticultural Research Station of Leibniz University in Ruthe. All trees were grafted on Gisela 5 rootstocks. Fruit were sampled in the mornings, broughtto the laboratory and processed on the same day. Fruits were individually selected for color uniformity and freedom from visible defects. Pedicels were detached by excising a length from the receptacle end of longer pedicels. Unless otherwise specified, pedicel length was standardized to 20 mm.

Our results demonstrate that the fruit draws water out of the pedicel, resulting in pedicel dehydration and yellowing when held under non-transpiring conditions. The conclusion is based on four observations: (1) the decrease in pedicel water content, (2) the decrease in diameter of pedicels remaining attached to the fruit,(3) potometric flow through the pedicel when incubated at 100% RH,and (4) the development of negative pressure in the pressure probe establishing hydraulic continuity between probe, pedicel, and fruit.All these changes were essentially absent in detached pedicels.Consistent with these observations is the slight increase in osmolarity of the attached pedicels, but not of the detached ones.

Pedicel shrivelling is caused by pediceltranspiration and also by osmotic dehydration. The relative importance of the two will depend on the water vapor concentration deficit of the atmosphere surrounding the fruit. Postharvest handling of sweet cherry fruit at low temperature clearly decreases the driving force for pedicel transpiration but it does not eliminate (or even much affect) the osmotic dehydration of the pedicel.

The latter is less dependent on temperature and hence, will occur even under the near ideal nontranspiring conditions of a refrigerated modified-atmosphere package. Given the mechanism of osmotic dehydration and its physiological basis, the options for preventing dehydration and consequently yellowing of the pedicels are more limited than previously imagined.