If I rinse fresh blueberries before I eat them, does that wash off the antioxidants? Why would washing blueberries before freezing them cause tougher-skinned berries?
The antioxidants in blueberries lie in the berries themselves, not in the pesticides residing on their skin.
Washing them before freezing means that water freezes on the outside. The water crystals puncture the skins of the berries, changing the texture.