Mahybe hygiene. Not knowing what you are doing for "excellent hygiene" makes answering more difficult. A mouth rinse and toothpaste called closys are formulated to neutralize the volatile sulfur compounds that cause breath problems.
Many things. I'm not sure one can attribute a foul smell in mouth specifically to saliva itself. Anything going on in your mouth, sinus, nasal cavity, throat, stomach etc. Can present itself as an unpleasant odor in your mouth. There are many dental as well as medical causes. See the following website and then consult with your dentist first, followed by ENT if necessary-http://smilesapartcosmeticdentist.Com.