This is a tricky one.. there is a raw sharp taste associated with onions.
The onions need some cooking before being pulped down with a whizz machine otherwise there is an unpleasant after taste of raw onion.
As for reducing acidity, we have several scientists here that maybe could light some shed, er shed some light on that.
I just realised after Georges post, the bicarbonate will reduce or neutralise the acidity but so would potato, which is also an ingredient in IfindforUs base sauce recipe.
Adding bicarb also gives a slightly creamy and fluffy texture to a curry which is identical to some restaurants we have here in Stockholm. I always thought this was the chefs skill in making curries before i realised it was a chefs secret.
Here is some onion information
http://en.wikipedia.org/wiki/OnionRegards Ashes