here I have a tree with fruit and thorns,its 30 years old the fruit has a gentle flavor but it is crunchy like an apple,it has a nut inside the fruit ,mom says it starts with an m,but she cant remember,I have pics
On a related note, your mom might be thinking of Mombin when she looks at the fruit; visually it's quite similar. This said, I agree with Salt and Michael - it's a Jubube.