Post harvest Management of Horticultural Crops (2+1)

Disinfestation

DISINFESTATION
Post harvest diseases of fruits, vegetables and flowers are caused by fungi and bacteria but viruses are rare. These exist either as parasite (on living matter) or saprophytes (dead produce). Most fungi require acidic pH (2.5 – 6) condition in which they grow and develop, while bacteria thrive best at neutral and few can grow at levels below pH 4.5. Bacteria therefore don’t usually infect fruits, normally but only vegetables and flowers.
Chlorine and sulfur dioxide are most widely used chemicals. Chlorine is probably the most widely used sanitizer. It is used in concentrations from 50 to 200 ppm in water to reduce the number of microorganisms present on the surface of the fruit. However, it does not stop the growth of a pathogen already established.

Mode of infection by microorganism
Fungal and bacterial infection can occur through mechanical injuries and cut surfaces of the crop, growth cracks and pest damage. They also infect through natural opening on the surface of the crop such as stomata, lenticels, cuticles and hydrathodes. Most fungi are able to penetrate the intact healthy skin of the fruits and vegetables. Many pathogens remain dormant on the surface of the produce for many weeks before visible symptoms of the infection occur.

Damage by microorganism
It mainly causes physical loss of the edible matter, which may be partial or total. Also affects marketability, particularly where mold growth is obvious on the produce surface. In some cases the superficial infection also make the produce either entirely unmarketable or at least reduce its economic value.
Example: Fungi Aspergillus flavus and A. parasitica which produce aflatoxin like mycotoxin on ground nut kernels, coconut, dry beans and some leafy foods. The apples juice is also affected by mycotoxin "patulin" produced by Penicillium patulum and P. expansum, P.urticae, Aspergillus clavatus when stored for too long before being processed. This mycotoxin is carcinogenic and has maximum permitted levels of 50 ppb in fruit juices.