The short answer is no. Sealing your grout will help to protect the grout and also make it easier to clean, but it does not change the environment. A shower / bathroom is obviously a wet area, with high levels of humidity – the perfect environment for mold to flourish. The best steps you can take to prolong the life of your grout and prevent mold build up are to use a quality grout and keep the area as well ventilated as possible.  Also, avoid the use of harsh chemicals and cleaners like bleach.