Preheat oven to 400 degrees F (200 degrees C). Grease muffin cups or line with paper muffin liners.
In a large bowl, sift together flour, baking powder, salt and sugar. In a separate bowl, combine egg, orange zest, orange juice, milk and vegetable oil. Stir egg mixture into flour mixture just until moistened; fold in raisins. Spoon batter into prepared muffin cups.
Bake in preheated oven for 20 to 25 minutes, until a toothpick inserted into center of a muffin comes out clean.