Preheat oven to 350 degrees F (175 degrees C).Grease and flour a 10 inch tube pan.
In a large mixing bowl, combine the egg whites and salt. Whip with an electric mixer until soft peaks form. Continue mixing while gradually adding the 1/4 cup of brown sugar and fructose. Whip to stiff peaks, but not blocky.
In a medium bowl, combine the egg yolks, brown sugar and fructose. whip with an electric mixer until stiff and pale. Gradually mix in the lemon juice. Remove from mixer and fold sifter flour in by hand with a rubber spatula. Fold 1/3 of the egg whites into the yolk mixture until well blended, then fold the yolk mixture into the remaining egg whites. Pour batter evenly into the prepared pan.
Bake for 30 to 45 minutes in the preheated oven, until a toothpick inserted comes out clean. Allow the cake to cool for 10 minutes in the pan before inverting onto a wire rack to cool completely.