Osmotic and elastic adjustment, and product quality in cold-stored carrot roots (Daucus carota L.)

Pressure-volume-analysis was used to investigate the variations in water re lations of carrot, harvested either 130 d (refered to as 'young') or 190 d ('old') after drilling, at intervals during cool (5 degreesC) and humid (> 98% RF) storage. The aim was to characterise changes in root water status w hich denotes an important determinant of internal product quality. Water po tential was measured with a scholander-type pressure bomb. Relative water d eficit (RWD) of stored roots remained low (approximate to 2%) and their pre ssure potential high (Psi (p) > 0.9 MPa) during an initial 40 d period. Bot h parameters then rapidly changed to new levels (RWD approximate to 4%; Psi (p) approximate to 0.5 MPa), and remained more or less constant for additi onal c. 100 d. Water potential and osmotic potential transiently decreased during early storage. Because maximum water content at water saturation rem ained constant throughout the study, the changes were due to active osmotic adjustment, i.e. a net accumulation of osmotically active solutes, manifes ted by the temporary reduction of the osmotic potential at water saturation ((S)Psi (pi)) and at turgor loss point ((TLP)Psi (pi)). This was accompani ed by a reversible decrease in tissue elasticity during the initial phase o f storage. All these changes were more pronounced in older carrots. The rel atively small changes in water deficit and turgor may indicate that carrot internal quality did not decline or even was improved during initial storag e. However, with prolonged storage the content of osmotically active substa nces decreased, and tissue elasticity increased. Thus, the quality of carro ts declined without serious water losses.