Some sugar free gums with xylitol, sorbitol, mannitol, aspartame, all of which do no harm to teeth also contain Malic and Citric acid. I found out malic acid can whiten or rid of superficial stains on teeth but citric acid only erodes enamel. So why do these 'good' for teeth gums contain these acids, particularly citric acid (other than for the sour taste)