Combine sugar and water in saucepan ans stir over medium high heat till sugar is dissolved. Just before mixture comes to a boil, remove from heat and cool slightly, cover and chill. Combine syrup, lemon juice and zest and blend well. Place in ice cream maker and freeze partially till sorbet is still soft. Add egg whites and complete churning. If useing a conventional freezer, freeze sorbet in a metal container. Thaw partially and spoon into a food processor or blender and beat till smooth and fluffy. Add egg whites and continue mixing till well blended. Return to freezer to freeze completely.