From a previous Blurtit answer:
Mark Mottian answered 7/2/2011
Salt behaves very deliquescent (having a strong affinity for moisture) due to the magnesium chloride, which acts as an impurity. Henceforth, when salt is applied to raw mango, the salt will absorb the juices from the mango due to the regular propensity of water to move to an area of high solute to equilibrate the concentration. In laymen's terms, the water level on the surface of the mango will deplete and somewhat dehydrate the fruit, making it relatively hard and dry.