담백 is an expression of taste which is not greasy but light and mild. 단백 is; 1) a shorten word of 단백질 which means protein. Normally, word 단백질 is preferred when saying protein. 2) synonym of 난백 and 흰자위, the white of egg. This meaning is very hardly used. If you saw 단백 in something about taste, it would be mistyped of 담백. 담백 and 단백 have totally different meaning, and word 단백 is not used very well.