Involved in galactitol catabolism. Catalyzes the oxidation of galactitol to D-tagatose. Can also catalyze the oxidation of D-sorbitol to D-fructose. galactitol + NAD(+) = H(+) + keto-D-tagatose + NADH H(+) + keto-D-fructose + NADH = D-sorbitol + NAD(+) kcat is 3.5 sec(-1) with galactitol as substrate. kcat is 4.4 sec(-1) with D-sorbitol as substrate. Carbohydrate metabolism. Up-regulated by growth on D-altritol or galactitol. Deletion mutant cannot grow on D-galactitol. Does not exhibit a growth defect when grown on D-altritol. Belongs to the short-chain dehydrogenases/reductases (SDR) family.