Eat More Strawberries. Strawberries contain malic acid, which removes discolorations on the surface of the teeth. Additionally, the berries' texture helps buff the enamel, creating a brighter, smoother appearance. To heighten the effects of strawberries as a natural teeth whitener, combine a crushed berry with one half of a teaspoon of baking soda. Once the mixture is complete, apply and leave on teeth for five minutes. Only do this once in a while, to keep the enamel of the teeth from breaking down.