Preheat oven to 400F. Line a 12-cup muffin tin with paper liners. Mix together the yogurt, oil, lemon juice, egg whites and lemon extract. In a larger bowl, stir together flour, sugar, baking powder, salt and lemon zest. Add the wet ingredients to the dry, and stir until just blended. Gently stir in the raspberries. Spoon batter evenly into the prepared muffin cups, filling about 3/4 full. Bake for 15-17 minutes, or until a toothpick inserted in the centre of the muffins comes out clean. Remove muffins from tin and place on a wire rack to cool. Makes 12 muffins.