Tevul Yom, Chapter Four, Mishnah One
If food that was tithe had been rendered susceptible to impurity by a liquid, and a tevul yom or one with unwashed hands touched it, terumah of tithe may still be removed from it in purity, since it only has third degree uncleanness, and third degree uncleanness counts as clean in hullin.
A tevul yom or one who has unwashed hands touches tithe. Both of these people are considered as having second degree impurity. They will cause the food to have third degree impurity. However, third degree impurity counts as clean if the food is hullinnon sacred. It only disqualifies terumah. Since tithe is considered hullin, the produce remains pure. Therefore, one may remove the terumah from this tithe, as is always done.
In other words, although we will separate terumah from it in the future, right now it does not have the status of terumah. Hence it is not disqualified.