Heat oven to 350 degrees. Butter a 9x5 in. loaf pan. Cream butter and sucanat in a large bowl. Add bananas, eggs yolk, vanilla, lemon juice, and baking soda; mix thoroughly. Stir in flour. Beat egg whites until stiff; gently fold into batter until well blended. Stir in hot water. Scrape batter into prepared pan. Bake until a wooden pick inserted in center comes out clean, about 45 minutes. Turn out of pan and cool completely.