ABSTRACT
Using a pressure bomb and an universal testing device the influence of postharvest handling stresses on water relations and on tissue elasticity of carrot roots was investigated. The interactive effects of osmotic content, the actual water volume and the tissue elastic properties, and their respective changes on product quality were characterized with pressure-volume analyses.
Independent of whether leaves were detached from the tap roots water potential declined by more than 200% during 2 days of storage at 18°C even if air humidity was > 98% RH. While osmotic potential was unaffected, turgor decreased substantially. Storing carrots at moderate air humidity (85% RH) let their water potential fall beyond the turgor loss point within 2 days. The effects of simulated mechanical stresses on water relations were less unequivocal. Repeated drops on different surfaces did not enhance the reduction of water potential in carrots during successive storage. Shaking roots on an oscillation-table stress-simulator resulted in a significant decrease in water potential. Enhancement of water losses due to mechanical stress depends on the degree of stress, i.e. the number of collisions during handling. Reduction of carrot water potential was highly correlated with an increase in tissue elasticity.
Carrots stored at low temperatures and very high air humidity retained a high water content and a relatively high turgor, achieved by both osmotic and elastic adjustment. Despite this, the increase in maximum osmotic potential with prolonged storage showed that the content of osmotic active substances decreased, thus lowering the product quality. Changes in elastic properties indicated that carrots became softer even without serious water losses.
