Post harvest Management of Horticultural Crops (2+1)

Deficiency of Calcium

Calcium is associated with more postharvest-related deficiency disorders than any other mineral. Ca deficiency disorders, such as blossom-end rot of tomatoes, can be eliminated by applying calcium salts as a preharvest spray. For others, such as bitter pit of apples, only partial control is obtained by preharvest sprays. Variability in the extent of control achieved is probably related to the amount of calcium taken up by the fruit. Postharvest dipping at sub-atmospheric pressures, which markedly increases the uptake of calcium, can result in total elimination of bitter pit. A substantial amount of the added calcium binds with pectic substances in the middle lamella and with cell membranes. Added calcium may possibly prevent some disorders by strengthening these structural components, without alleviating the original causes of the disorder. Strengthening cell components could prevent or delay the loss of sub-cellular compartmentation and the associated chemical and enzyme mediated reactions that cause browning symptoms.

Table: Calcium-related disorders of fruit and vegetables
Produce	Disorder
Apple	Bitter pit, lenticels blotch, cracking, internal breakdown, water core
Avocado	End spot
Bean	Hypocotyl necrosis
Brussels sprout	Internal browning
Chinese cabbage	Internal tipburn
Carrot	Cavity spot, cracking
Celery	Blackheart
Cherry	Cracking
Chicory	Brownheart, tipburn
Lettuce	Tipburn
Mango	Soft nose
Parship	Cavity spot
Pear	Cork spot
Peppers	Blossom-end rot
Potato	Sprout failure, tipburn
Tomato	Blossom-end rot, blackseed, cracking
Watermelon	Blossom-end rot


Adding calcium to intact fruit or fruit slices generally suppresses respiration, but the response is concentration-dependent. The activities of isolated pectic enzymes have shown differential responses to calcium concentration. For example, the activity of pectin methylesterase is initially increased by increasing concentrations of calcium but is inhibited at higher concentrations, while the large form of endo polygalacturonase is stimulated slightly by concentrations of calcium that inhibit the smaller forms of the same enzyme.