What's the function of acerola powder in bread? While I was reading the ingredients list of a supermarket-bought bread (in the Netherlands) the other day, one of them caught my eye: acerola powder. I know acerola is a fruit with a high vitamin C content but why would it be used in bread?

I don't think it was for its particular flavor since it was just a regular soft bread, not a sweet/flavored bread (more precisely "bakkersballen" with spelt). And if it's as a preservative / conditioner, why not just use ascorbic acid?
The only functional reason that comes to mind is indeed the vitamin C content. Vitamin C makes for quite tough gluten, so it is frequently used in bread making. 

The question about the choice of acerola powder over ascorbic acid can only be answered with certainty by the person who made that choice. An obvious guess would be that it was done for marketing reasons.