Malic acid in apples boosts saliva to wash away acids. Toothpastes with bromelain, a compound in pineapple, help whiten teeth. But there's no evidence that eating these fruits will make your grin gleam. Skip the strawberries, too. A study in Operative Dentistry found that brushing with a mixture of them and baking soda had no whitening effects. Even worse, the citric acid in strawberries can break down enamel, the outer shell of your tooth.