Preheat oven to 180°C. Whisk egg whites and half portion of sugar in an electric mixer until just stiff and mixture holds its shape.
Whisk egg yolks and sugar until light and creamy. Add grated orange and lemon rind. Add orange and lemon juice and stir well. Sift in self-raising flour with 1/4 tsp salt and fold gently with a metal spoon. Stir in corn oil.
Pour egg yolk mixture into egg white mixture. Carefully and gently mix with a spatula until batter is even.
Pour mixture into a 20cm ungreased tube pan. Bake in preheated oven for 40 minutes or until cake is well browned on the surface.
Remove cake from the oven and invert mould immediately. Leave aside to cool completely before removing from the mould.