Orange Oat and Flax Bran Muffins

I got this recipe from the food column of our newspaper a long time ago, but I think it was originally from Outspan Oranges. I have made alterations to the recipe, using dry buttermilk powder, and changing the raisins to either dried cranberries or fresh blueberries. The original recipe just cut the oranges into quarters, and blitzed them in the food processor, but I prefer to zest them with a microplane grater, peel off the pith, and chop them finely, reserving the juice to add with the liquids. I often add nuts to the batter as well. If using buttermilk powder, (I use 1/3 cup), mix it with the flour, and add 1 cup of warm water to the wheat bran and let it cool before mixing with the other ingredients.