I don't know about traces in mango. Mango sap is really corrosive, particularly if you pick the fruit while it is still green. Years ago my family had a smallish mango tree in our front yard (some varieties of mango grow quite well even as far south as Sydney) and we would get 30 or 40 big mangoes off it every year - the branches would bend under the weight of the fruit until they were touching the ground.

A friend at work asked me to pick him some green mangoes, and told me to be very careful of the sap. So, of course, I completely ignored his advice, and as I snapped off a large green mango the sap sprayed out a good foot or two from where I had snapped the fruit off and I felt a burning sensation on my face. I didn't think much of it until later when I tried to clean my glasses and found that the sap had eaten into the plastic lens and left a permanent ragged furrow. The sap had also eaten the skin off my chin and left me with a nasty scab.  

Ripe mango sap is much less corrosive. And nobody believed me about the mango sap, except the friend who had warned me.