Chitosan forms a translucent film on surface of fruits and vegetables, blocking transpiration and decreasing loss of moisture. 
The chitosan film is of the characteristics of permeability selecting, stopping oxygen, inhibiting let of carbon dioxide, allowing transgressing of ethene generated during the storage period and restraining respiration of fruits and vegetables. 

Chitosan can prevent decrease of sugar and acid content during the storage period.
 
Chitosan can reduce activity of relevant enzyme during the storage period of fruits and vegetables, restrain generation of MDA and improve stability of cellular membrane.  
Chitosan can improve SOD activity in fruits and vegetables, reducing damage of free radical to cellular membrane and postponing cell caducity, i.e., prolonging the storage period. 
Chitosan can induce a series of defensive reaction mechanism of fruit and vegetables, blocking attack of pathogenic bacteria.