Why Is My White Sweet Potato Turning Black? I started cutting a white sweet potato. But within minutes an area on the outside of the potato started turning black/brown. Other sides of the cubed chunks didn't seem as affected. Here's a photo with the black and better bits separated. Even the good ones were rapidly browning and oxidizing in a speckled fashion.
It is, as you said, oxidation. As soon as you cut them, put them in a bowl under water. Kills the oxygen supply/reaction.