Effect of postharvest calcium chloride treatments on tissue water relations, cell wall calcium levels and postharvest life of 'Golden Delicious' apples.
Saftner, R.A., Conway, W. S. and Sams, C. E.
Journal of the American Society for Horticultural Science. Volume 123, Number 5, Sept 1998. Pages 893-897.
1998
บทคัดย่อ
Changes in tissue water relations, cell wall calcium (Ca) levels and physical properties of Ca-treated and untreated 'Golden Delicious' apples (Malus x domestica Borkh.) were monitored for up to 8 months after harvest. Pressure infiltration of fruit with CaCl2 solutions at concentrations up to 0.34 mol(.)L-1 reduced both fruit softening and air space volume of fruit in a concentration-dependent manner. Turgor potential-related stress within the fruit persisted during storage and was higher in Ca-treated than in untreated fruit. Fruit that were pressure infiltrated with CaCl2 solutions between 0.14 and 0.20 mol(.)L-1 and then waxed to reduce water loss during storage showed no peel injury. Calcium efflux patterns from apple tissue disks indicated two distinct Ca compartments having efflux kinetics consistent with those for cell wall Donnan-phase bound and water free space soluble Ca. At Ca concentrations up to 0.20 mol(.)L-1, cell wall bound Ca approached saturation whereas soluble Ca showed a linear dependence. At higher external Ca concentrations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased up to 48%. The osmotic potential of apples harvested over three seasons ranged between -1.32 and -2.33 MPa. In tissue disks, turgor potential changes caused by adjusting the osmularity of the incubation solution with CaCl2 or sorbitol were accompanied by changes in the osmotic and water potentials of the tissue. In CaCl2 solutions upto 0.34 mol(.)L-1, turger potential was greater than or equal to 0.6 MPa in tissue incubated in 0.14 or 0.17 mol(.)L-1 solutions of CaCl2 and was more than 3 times higher than in tissues incubated in low (less than or equal to 0.03 mol(.)L-1) or high (greater than or equal to 0.27 mol(.)L-1) concentrations of CaCl2. At osmotically equivalent oncentrations, turgor potential was up to 40% higher in Ca- than in sorbltol-treated time. The results suggest that postharvest treatment with 0.14 to 0.20 mol(.)L-1 solutions of CaCl2 are best for maintaining fruit water relations and storage life of 'Golden Delicious' apples while minimizing the risk of salt-related injuries to the fruit. While higher concentrations of CaCl2 may better maintain firmness, these treatments adversely affect fruit water relations and increase the risk of fruit injury.