1. Place egg substitute, half of grapefruit juice, sugar, salt and dry mustard in blender container. Cover and blend to combine thoroughly. Turn blender on high speed and slowly pour half of oil in thin stream through opening in top of blender cover. Pour in remaining grapefruit juice in thin stream, then slowly add remaining oil in thin stream. Blend until smooth and thick. Stir in grapefruit zest, place in covered container and refrigerate for at least one hour or until ready to use.