What causes brown spots in the flesh of cooking apples from my tree, and can the apples still be used?

I'm having issues with brown spots in the flesh of cooking apples from my tree. The fruit is peppered, but the outside skins look perfect. Can you please suggest what might be causing this, and can the apples still be used?

Brown spots in the flesh of cooking apples are generally caused by a calcium or boron deficiency, which is more prevalent in dry summers and on acidic soils. The shortage of these nutrients can result in a breakdown of the cell walls, leading to pitting. The apples can still be used, but they may not keep as well. Apply a foliar spray of a complete plant food such as Miracle-Gro a couple of times during early and mid-summer. Mulching can also help to retain moisture and sustain the trees during prolonged dry spells.