Beat sugar and butter at medium-high speed of a mixer until well-blended (about 7 minutes). Add eggs and egg white, 1 at a time, beating well after each addition. Combine buttermilk, rind, vanilla, and baking soda. Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and salt, stirring well with a whisk. Add flour mixture to sugar mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Fold in pomegranate seeds.
Spoon batter into an 8 x 4-inch loaf pan coated with cooking spray. Bake at 350° for 1 hour or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes on a wire rack; remove from pan. Cool completely on wire rack.