Why did the apple skins turn blue/purple-ish in my apple pancakes the next day?

Question

Yesterday for dinner I made apple pancakes. I cut the apple into small pieces (with the skin on) and just put it into my pancakes batter. The skin was dark red. After cooking it, everything was looking fine.

Now the next morning, I took out the pancakes from the fridge (on a plate covered with aluminium foil) and noticed that the apple skin turned blue/purple-ish. The apple flesh still seems normal (white/yellow), so I'm confident it is the skin that was originally dark red.

It seems safe to eat, smell and taste are completely fine. I mean it's only been 1 single night after all.

So why did this happen?
I've never heard of this. I've baked apple cake before (with skin) and it never turned blue-ish even after days.

The recipe I used includes flour, sugar, baking powder, salt, eggs, oat-almond milk, molten butter and 1 big apple.

After closer inspection it does look more grey-ish with dark purple-ish around the edges.
Unfortunately I can't provide images as the pancakes are long gone.

Oh and as someone has mentioned, the pancake interior around the apple piece was coloured purple-ish. As if some of the color of the apple skin "leaked out".

Answer 1

I feel fairly confident that what you see is anthocyanins (naturally present in apple skin) reacting with some leavening in your pancakes.

Here's a link that explains in more details, but I'll summarize: https://extension.psu.edu/fruit-color-promoting-red-color-development-in-apple

Anthocyanins are a natural pH indicator present in many fruits and vegetables. Red cabbage and blueberries are common examples. Elderberries and black sweet rice, and even many flowers also contain these compounds.

And they turn red in the presence of acid like vinegar, buttermilk, or fruit juice, and blue in the presence of a base like baking soda or baking powder.

So when you bake or cook with certain fruits that contain anthocyanins, you might be surprised that your blueberry muffins came out green, or that your "purple" rice is hot pink. This is because anthocyanins are water soluble, so they'll disperse throughout what you're cooking easily, and visually indicate the pH. You may even notice a blue shadow in the pancake around or under the apple skins.

But if this is the case you are a-okay. Judging by the contents of the recipe, it only contains a base for leavening, but no acid for it to react with. So it makes perfect sense that your apples, the only acidic component, would react and turn blue. If you want to get more rise, include some buttermilk or lemon juice next time. When it reacts with your leavening you'll get more floof, and your apples will stay red (or pink at least.)