Egg Challah

So I made my first egg challah. I picked Joan Nathan's recipe after looking at all the recipes.

The house smelled like Jewish heaven. It looks great and tastes great.

I know the store bought challahs have that special ingredient baked in it to preserve  itfor freshness, etc.

Today is the 2nd day and already I feel the loaf starting to get hard.

Is there an ingredient I can use to preserve its freshness?

Any help is greatly appreciated.