Re: How can we preserve fresh mangoes (for export) for 3-4 months

Most likely you can not.  Ripe vegetables will spoil quickly.  The best 
way to prolong the shelf life as long as possible is to keep the produce 
as cold as possible without freezing.  Freezing will damage the cellular 
structure and hasten spoilage.  The produce must also be kept dry.  
Increase moisture will promote microbiological growth and spoilage.  The 
use of certain gasses may also lengthen shelf life.  A combination of 
nitrogen and carbon dioxide is common.