This is a special recipe made without gluten. Preheat oven to 180ºC . Grease a 9 x 13 cm loaf pan. Sift flour, baking soda, baking powder, salt and unflavored gelatin together. Cream margarine, sugar, egg yolks and vanilla thoroughly. Continue beating until mixture is light. Mix in lemon peel, mashed banana and yoghurt. Add dry ingredients. Beat egg whites to stiff peaks but not so they are dry. Fold egg whites into the mixture. Place in the greased loaf pan. Bake for 1 hour.