Why Did My Potato Latkes Turn Black After Storing Them in the Fridge?

Q:

I just made a batch of potato latkes and fried them up until crispy brown. They tasted excellent, but we stored them in the refrigerator, wrapped up and continued to eat them for a few days. After the third day, the center on some of the potato pancakes turned black. Can you tell me why or what to do to prevent it? I added lemon to the shredded potatoes while I shredded them to prevent discoloration. I used 12 large Idaho® potatoes, 10 eggs, a half cup of Matzo Meal, a half cup of high gluten flour, a tablespoon of baking powder, salt, pepper and two grated Spanish onions; I fried them in a blended oil. Could the high gluten flour have something to do with it?

A:

I am guessing the onions accelerated the potatoes turning black or the potatoes were not fully cooked in the middle (make the same thickness and not mounded up in the middle next time to try this out). I used to run into this when different people made pizza, especially with fresh sausage. The piled high section, in the middle of the pizza, never got fully cooked.